CN114114171A - Multifunctional internal field scattering imaging measurement system, method and application - Google Patents
Multifunctional internal field scattering imaging measurement system, method and application Download PDFInfo
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- CN114114171A CN114114171A CN202111168608.1A CN202111168608A CN114114171A CN 114114171 A CN114114171 A CN 114114171A CN 202111168608 A CN202111168608 A CN 202111168608A CN 114114171 A CN114114171 A CN 114114171A
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- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
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- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
- G01S13/88—Radar or analogous systems specially adapted for specific applications
- G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
- G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
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Abstract
The invention belongs to the technical field of electronics and scientific application, and discloses a multifunctional internal field scattering imaging measurement system, a method and application.A groove fixed by screws is added above a carrying platform, a fixed hollow pipe is arranged above the groove, the hollow pipe is provided with internal threads, and a support with external threads is arranged above the hollow pipe and supports a flat plate; the antenna horn is fixed on a flat plate, and a connecting device is arranged behind the flat plate and used for connecting the flat plate with the ball screw; marking the setting angle of the polarization adjusting device; a ring-ball rotary working table is arranged below the ball screw main body and connected with a track, and the track center and the carrying platform are aligned in advance. The experimental accuracy is improved by adding angle marking to polarization adjustment and pitching adjustment; the position of the measuring system is adjusted in advance, so that the time of an experiment preparation link is shortened; the experimental items which can be completed by a microwave darkroom, such as a strip SAR imaging experiment, a different polarization RCS measurement experiment and the like, are added.
Description
Technical Field
The invention belongs to the technical field of electronics and scientific application, and particularly relates to a multifunctional internal field scattering imaging measurement system, a method and application. The main content is the transformation of an electromagnetic wave measuring system in a microwave darkroom, the device involved in the transformation mainly comprises a rotary table for placing an object to be measured and an antenna bracket for fixing a radar, and related experiments comprise an RCS measuring experiment, a polarized RCS measuring experiment, an SAR imaging experiment, a polarized SAR imaging experiment and a strip-type SAR imaging experiment.
Background
At present, a microwave anechoic chamber is also called as an anechoic chamber, and the inner wall of the anechoic chamber is covered with a layer of substance capable of absorbing electromagnetic waves, which is called as a wave-absorbing material, and the most common wave-absorbing material is polyurethane wave-absorbing sponge SA. Generally, most of wave-absorbing materials used for the inner wall of the microwave anechoic chamber are sponge cone-shaped absorbers, and the cone top is coated. With the wave-absorbing material, a 'free space' condition is artificially manufactured, which provides an ideal electromagnetic environment for simulating RCS and SAR imaging of an object under the outdoor condition. Radar Cross Section (RCS) is one of many concepts that have conventionally been transferred to Radar target characteristics during antenna development, and is not a real-world area, but is hypothetical. RCS is a physical quantity used to describe the strength of a signal reflected from an object after being illuminated by a radar signal. It can be understood that: when the ideal conductor ball faces the same environment and the intensity of the echo signal obtained when the radar signal is the same as that of the echo signal of the target, the RCS is the projection area of the ideal conductor ball. Synthetic Aperture Radar (SAR) was first used in the late 20 th century 50 s, on several strategic reconnaissance aircraft. The method synthesizes the radar with smaller aperture into the radar with large aperture by utilizing the motion of the radar. SAR imaging has developed rapidly once proposed, because the larger the radar aperture, the higher the resolution of the imaging.
Since the emergence of the microwave darkroom technology in the early 50 s of the last century, the development of the microwave darkroom technology is rapid abroad, and more than 400 microwave darkrooms are built in the light America. The microwave darkroom which is famous abroad at present comprises an RCS testing field of the Belifield microwave darkroom Ohio State university, a Kyoto technical research institute, a millimeter wave system of Boeing company and the like. The microwave darkroom in China starts late, and the national requirement on radar is higher and better, so that many enterprises and electronic colleges and research institutes in China start the research and construction of the microwave darkroom. Generally, a measurement system of a microwave anechoic chamber comprises a carrying platform, an antenna bracket, a shielding wall, a control system, a connecting cable and measurement software. The object to be measured is placed to the effect of cargo platform, realizes the rotation of object. The support object of the loading platform, which is directly contacted with the object to be detected, is foam, and the foam is used for reducing the influence of the surrounding environment on echo signals as much as possible; the antenna bracket is used for supporting the antenna, achieving the polarization state required by the horn antenna, freely moving, completing the track movement of certain experiments (such as strip SAR imaging) and the like; the shielding wall is used for separating the loading platform from the antenna bracket and reducing the influence of the loading platform on electromagnetic echo as much as possible; the control system mainly controls the rotation angle of the loading platform and the receiving and sending of horn antenna signals; connecting cables are connected with instruments required by experiments, such as a signal transmitter, a horn antenna, a power amplifier and the like; and the measurement software stores and analyzes experimental data. The advantages of the microwave darkroom mainly include: the climate influence under outdoor conditions is not needed to be worried about; the repeatability of the experiment is strong, the movement of the target to be detected is not worried about, and about one third of the time of a target range is saved; because the environment is indoor, external electromagnetic signals can not enter, so no radiation interference exists, and the indoor electromagnetic waves can not be transmitted to the outside and can not be limited by electromagnetic radiation supervision; the external detector can not detect indoor electromagnetic signals, and the confidentiality is high.
The common polarization modes of radar are four types, namely HH, VV, VH and HV, the first two are codirectional polarization, and the second two are orthogonal polarization. Wherein H represents horizontal and V represents vertical. HH denotes horizontal transmission and horizontal reception, VV denotes vertical transmission and vertical reception, VH denotes vertical transmission and horizontal reception, and HV denotes horizontal transmission and vertical reception. The echo signals of the same object under different polarizations are different, and the displayed object characteristics are also different. For example, when measuring a marine target object, the L-band acts better under HH polarization; for grass and roads, the measured data for horizontal polarization is better. Various polarization measurements are matched, so that various information of the object can be displayed more completely.
The specific steps of the existing microwave darkroom measurement system for carrying out the RCS measurement experiment or SAR imaging experiment of an object are as follows: preparing, namely finding a central point of the antenna bracket which is opposite to the loading platform by using laser emitted by a laser, and keeping the transverse positions of the loading platform and the antenna still; an experimenter loosens a rotating handle on the antenna bracket and manually adjusts the up-and-down movement of the bracket, so that a cross rod of the bracket is adjusted to be in the same horizontal line with the carrying platform; horizontally moving the horn antenna to enable the center position of the horn antenna to be just aligned with the carrying platform; after the horn antenna is aligned, the levelness of the horn antenna is adjusted, screws behind the horn antenna are loosened to enable the horn antenna to rotate slightly freely, a leveling instrument is placed on the antenna, the position of bubbles is observed, and the antenna horn is fixed after leveling; and finally, placing the object to be measured on an object carrying platform, setting the polarization orientation of the antenna and other parameters of the test software according to the measurement requirement, and starting to measure. In the measurement process, it usually takes a lot of time to adjust and calibrate the calibration in the early stage, which mainly summarizes the following reasons: firstly, the cross bar for loading the antenna has one end fixed, and the other end is supported by another adjustable stand column, and if the height of the stand column at the other end is not in place, the weight of the antenna bracket is mainly supported by the stand column, so that the cross bar becomes out of level, and the cross bar needs to be checked whether to be parallel by means of a laser, and then the height is finely adjusted manually. The upright post and the cross rod of the fixed cross rod are integrated and have certain weight, and the experiment personnel need to move manually when adjusting the height and are extremely difficult to move to the required position. Secondly, when the horn antenna is adjusted to be horizontal, the horn antenna is required to be operated on the upright post, the upright post has a certain height, and the leveling instrument is not easy to use. Thirdly, the foam of the object placed on the object carrying platform is not fixed, and during the object placing process, experimenters often touch the foam to cause the foam to shift, and the calibration work can be restarted.
Through the above analysis, the problems and defects of the prior art are as follows:
(1) the foam that directly supports the object to be measured on the objective platform is not fixed, often touches by mistake when making preparation work, leads to many times of repetition of calibration work easily. When doing the experiment, the objective table often need rotate according to the demand of experiment, if the foam on the objective table rotates the in-process and removes, just the calibration of earlier stage has lost meaning.
(2) The loading platform and the antenna bracket are not on the same horizontal line, the height of the loading platform is only fixed to a plurality of heights, the adjustment process of the antenna bracket is complex and laborious, and time is wasted and accuracy is low when the loading platform and the antenna are leveled.
(3) The distance between the object carrying platform and the antenna bracket is fixed, and different distances cannot be measured.
(4) The horn antenna has a single polarization mode, and scales are not arranged on the support, so that the measurement under the condition of multi-polarization or different pitching angles cannot be met.
(5) Still need artifical adjustment when antenna boom adjusts from top to bottom, waste time and energy and the accuracy is not high.
The difficulty in solving the above problems and defects is: the microwave darkroom has strict requirements on the inner wall of the darkroom, and the influence of a measurement system on electromagnetic wave signals is reduced under the condition that all experiments supported and completed by the microwave darkroom can be realized during modification. And the whole measuring system needs to be redesigned due to excessive modification projects, and the problems to be considered are many, the workload is large and the complexity is high.
The significance of solving the problems and the defects is as follows: the microwave darkroom is modified, firstly, the preparation work of the current measuring process can be simplified; and secondly, the improved microwave darkroom measuring system has greatly improved accuracy because the antenna bracket and the carrying platform are fixed on the same line in advance. Finally, the antenna after transformation can move back and forth relative to the loading platform, and antenna horn also can carry out different polarization according to the scale of predetermineeing in advance, and the setting of different every single move angles has promoted the measurement content in microwave dark room laboratory greatly, and the experiment that can go on has increased a lot.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a multifunctional internal field scattering imaging measurement system, a method and application.
The invention is realized in this way, a multifunctional internal field scattering imaging measurement system, which is provided with:
a carrier platform;
a groove fixed by a screw is additionally arranged above the carrying platform, a fixed hollow pipe is arranged above the groove, the hollow pipe is provided with an internal thread, and a support column with an external thread is arranged above the hollow pipe and supports a flat plate;
the antenna horn is fixed on a flat plate, and a connecting device is arranged behind the flat plate and used for connecting the flat plate with the ball screw;
marking the setting angle of the polarization adjusting device; a circular ball rotary worktable is arranged below the ball screw main body, the worktable is connected with a track, and the track center and the loading platform are aligned in advance.
Further, the diameter of the externally threaded strut is 40 mm.
Further, a foam frustum is placed on the flat plate.
Further, the maximum limit height of the flat plate from the hollow pipe is 320mm, and the maximum height of the object from the ground is 2114 mm.
Furthermore, the flat plate and the foam frustum directly supporting the object above are in a sawtooth shape and are mutually meshed.
Furthermore, a connecting device is arranged behind the flat plate, the flat plate is connected with the ball screw, and the antenna horn can move up and down freely through a motor with the rotation speed of 1800 rpm below the flat plate.
Another object of the present invention is to provide an application of the multifunctional internal field scatter imaging measurement system in RCS measurement experiments at different distances, including:
the electric field of RCS is defined as:
wherein r represents the distance from the measuring radar to the object to be measured, EiAnd HiIndicating the intensity of the electromagnetic wave of the incident signal emitted from the emitting end, Es(r) and HsAnd (r) represents the electromagnetic field intensity of the echo signal measured by the collecting end. RCS is a scalar quantity, with the unit m2Usually written in logarithmic form, called decibel square meters, written as dBsm:
σdBsm＝10lgσ(r)；
the data processing method for target RCS measurement comprises the steps of firstly measuring to obtain an echo signal, and calculating the value of the target RCS in a reverse mode through a radar range equation, wherein the radar range equation is as follows:
wherein, PrTo receive power, PtIs the transmit power, G is the antenna gain; in the formula except PrExcept the sigma, when other parameters are unchanged, the value of RCS is only in direct proportion to the received power; the RCS and received power relationship is as follows:
wherein σ0To calibrate the RCS value of the target, P0The received power is used for calibrating the target mapping quantity under the same measuring condition; standard metal ball or metal flat plate is used as calibration target, sigma in the formula0And P0For a given measurement system, the quantities are known in the same experiment, so that for any object that needs to be measured, only P is measuredrConverting the RCS value of the target;
in practical experimental measurement systems, the power is replaced by voltage:
after computer processing, a plot of the RCS of the target is plotted.
Another object of the present invention is to provide an application of the multifunctional internal field scatter imaging measurement system in RCS measurement experiments under different polarizations, including:
the measured RCS value of the target is dependent on the polarization of the transmit and receive antennas, and the transmit and receive polarizations are decomposed into two mutually orthogonal polarization components as follows:
Et＝Etvcosγt+Ethsinγt
Er＝Ervcosγr+Erhsinγr；
in the formula, EtAnd ErIs arbitrary, γtAnd gammarThe included angle between the electric field direction of the transmitting and receiving signals and the vertical direction, the angle marks t and r represent the transmitting and receiving signals, and v and h represent vertical and horizontal polarization; representing the components of the received field by the field components of the incident wave, the transform coefficients constituting a scattering matrix:
Erv＝SvvEtv+ShvEth
Erh＝SvhEtv+ShhEth；
where each S is a complex number, the scattering matrix is a set of four dimensionless complex numbers:
the relationship between the elements of the electric field scattering matrix and the elements of the RCS scattering matrix is:
σij＝|Sij|；
the matrix in both types is composed of four pluralitiesComposition, eight quantities need to be measured, four amplitudes and four phases respectively; firstly, the frequency phase at the radar can only be measured in a relative sense, taking into account the propagation distances of the incident and scattered waves; secondly, when no absolute phase is adjusted, one of the phase relations among the four elements is taken as a reference; finally, due to reciprocal cross-polarization terms (σ)vhAnd σhv) Must be equal and the necessary independent parameters describing the radar scattering cross-section matrix are reduced to five.
Another object of the present invention is to provide an application of the multifunctional internal field scatter imaging measurement system in SAR imaging experiments under different polarizations, including: decoupling the distance direction and the azimuth direction, and respectively finishing the two parts as two one-dimensional treatments; the method specifically comprises the following steps:
(1) distance direction processing of RD algorithm
The complex expression of the chirp signal is:
wherein the content of the first and second substances,
f0is an initial carrier frequency, tau is a signal pulse width, and K is a frequency modulation slope;
writing the echo signal of the target into the following form:
s(τ,ta)＝σ*h1(τ,ta)*τh2(τ)；
wherein the content of the first and second substances,
where τ is the fast time component of time t，taSlow time component of time t, convolution symbol, h1Indicating the modulation of the azimuth direction, h2Indicating a modulation of the distance direction; the distance-wise matching function is:
gr(τ)＝s0(-τ)exp[-jπkrτ2]；
distance-wise processed signal:
sr(τ,ta)＝σ*h1(τ,ta)*τAr(τ)；
wherein A isr(tau) is the envelope of the distance processed signal, the envelopes of the emission signals are different, the envelope of the distance processed signal is changed accordingly, and the distance processed signal is a sinc function;
(2) range migration correction process
Decoupling is carried out, then two one-dimensional signal processing are carried out, decoupling is obtained, and range migration correction processing is carried out;
the distance-wise processed signal is rewritten as:
when the range migration correction is carried out, the formula is rewritten as follows:
wherein R isrefFor reference distances that do not vary with slow time, R (t) in the signal before overwritinga) Doing a second order Taylor expansion, then the formula is rewritten again as follows:
to pair
Fourier transform of azimuth direction is carried out to obtain a squareBit direction frequency domain signal:
(3) orientation processing of the RD algorithm:
azimuth matching function:
the processed signals are:
wherein A isa(ta) Is a sinc function to process the envelope of the result.
Another object of the present invention is to provide an electromagnetic wave measuring system in a microwave darkroom, which uses the multifunctional internal field scattering imaging measuring system.
By combining all the technical schemes, the invention has the advantages and positive effects that: the invention mainly solves the problems in the experimental processes of the existing microwave darkroom; mainly to antenna boom and objective revolving stage: the main solution is as follows: (1) aiming at the problems that the carrying platform can not freely move up and down and the foam is not fixed, the transformation is carried out by a threaded lifting platform and a tooth-shaped meshing method. (2) Aiming at the problems that the antenna support is extremely difficult to adjust and the polarization mode of the horn antenna is single, a method of redesigning the support main body and adding angle marks to the device for adjusting polarization is selected for modification. (3) Aiming at the problem that the antenna and the object to be measured are not aligned well, a guide rail which is fixed in advance is used for pre-positioning. (4) The pitching angle adjusting function of the horn antenna is added. The invention solves the problems encountered in the test of the existing microwave anechoic chamber measuring system and improves the accuracy in the test adjustment process. Meanwhile, experiment contents which can be completed in a laboratory are enriched, and the measuring system can meet RCS measuring experiments of different distances, RCS measuring experiments under different polarizations and strip SAR imaging experiments, namely SAR imaging experiments under different polarizations.
Aiming at the problems encountered in the experimental process, the invention improves the original microwave darkroom measuring system, such as the free lifting of a loading platform and the like; the experimental accuracy is improved by adding angle marking to polarization adjustment and pitching adjustment; the use time of an experiment preparation link is shortened by pre-adjusting the position of a measurement system (such as pre-alignment of a guide rail and an object carrying platform); the experimental items which can be completed by a microwave darkroom, such as a strip SAR imaging experiment, a polarized RCS measurement experiment and the like, are added.
Drawings
Fig. 1 is a schematic structural diagram of a multifunctional internal field scatter imaging measurement system provided by an embodiment of the present invention.
Fig. 2 is a flowchart of a multifunctional internal field scatter imaging measurement method according to an embodiment of the present invention.
Fig. 3 is a schematic diagram of scanning modes of three kinds of SAR imaging provided by an embodiment of the present invention.
Fig. 4 is a flowchart of the RD algorithm according to an embodiment of the present invention.
Fig. 5 is a wiring diagram for RCS experimental measurement provided by an embodiment of the present invention.
Fig. 6 is a schematic view of a freely liftable loading platform after the microwave darkroom provided by the embodiment of the present invention is modified.
Fig. 7 is a schematic view of an antenna bracket controlled by a motor to freely ascend and descend after a microwave anechoic chamber is modified according to an embodiment of the present invention.
Fig. 8 is a schematic view of a device for connecting a horn antenna and a ball screw after a microwave anechoic chamber is modified according to an embodiment of the present invention.
Fig. 9 is a schematic diagram of an antenna bracket with an angle mark after a microwave anechoic chamber is modified according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In view of the problems in the prior art, the present invention provides a multifunctional internal field scatter imaging measurement system, method and application thereof, which will be described in detail with reference to the accompanying drawings.
As shown in fig. 1, the multifunctional internal field scatter imaging measurement system provided by the present invention comprises: a loading rotary table, an antenna bracket, a guide rail and the like.
Those skilled in the art can also implement the multi-functional internal field scatter imaging measurement system provided by the present invention by using other steps, and the multi-functional internal field scatter imaging measurement system provided by the present invention in fig. 1 is only one specific embodiment.
As shown in fig. 2, the multifunctional internal field scatter imaging measurement method provided by the present invention comprises the following steps: the method comprises the following steps of experiment preparation, experiment instrument wiring, spectrometer parameter setting, empty background measurement, calibration body measurement, object measurement and measurement under other polarization states and different distances required by subsequent experiments.
The technical solution of the present invention is further described below with reference to the accompanying drawings.
As shown in fig. 1-9, the present invention improves the following problems that the loading platform can not move up and down freely and the foam is not fixed: a groove fixed by a screw is additionally arranged above an original platform, a fixed hollow pipe is arranged above the groove, and the hollow pipe is provided with internal threads. And a pillar with external threads and the diameter of 40mm is arranged above the foam cone, and supports a flat plate on which a foam cone can be placed. The up-and-down movement of the loading platform can be realized by matching the hollow internal thread pipe with the external thread strut, the maximum limit height of the flat plate from the hollow pipe is 320mm, the maximum height of the object from the ground is 2114mm, and the requirement of laboratory measurement at ordinary times can be met. The foam frustum design that dull and stereotyped and top directly supported the object is the cockscomb structure, can sting each other together, when carrying out experiment preparation work, even the experimenter has touched the foam frustum by accident, can not take place to shift yet, and when the objective platform rotated, the foam frustum also can not take place to remove easily.
The invention is improved aiming at the problems of the antenna bracket as follows: firstly, the antenna horn is fixed on a flat plate, a connecting device is arranged behind the flat plate, the flat plate is connected with a ball screw, and the antenna horn can move up and down freely through a motor with 1800 rpm below. Secondly, the place of fixing the antenna horn on the flat plate is also improved, and data of different horn antennas in different polarization states are often required to be measured when various tests are performed. Therefore, the device for fixing the horn antenna can rotate. The laboratory staff can only choose horizontal or vertical polarization when adjusting the polarization before the measurement system is improved, and the laboratory staff also needs to expend time and labor for adjustment. The invention adds the angle marking to the device for adjusting polarization, is more convenient in polarization adjustment, provides more choices of different polarization angles for experiments, and enriches the experiment content. In the early development stage of the radar, when the technical level is not developed enough, the radar is often only used for positioning targets. In the development of radar, along with the increase of the technological level, the requirements on the radar are increased, and the position of a target and the shape of the target are required to be known. Therefore, the target to be measured is changed from a point target to an extended target, when the extended target is measured, data detected by the radar at different angles are different, and experimenters need to fully consider the point when performing indoor experiments. Therefore, the device for fixing the antenna horn is added with the function of up-down pitching, and is also marked with scales, so that the requirements of echo signal measurement experiments under different pitching angles of a target are met. Finally, a ring ball rotary workbench is arranged below the ball screw main body, the workbench is connected with the track, the track center and the carrying platform are aligned in advance, and the track and the carrying platform are fixed on the ground and cannot be moved easily due to external force, so that longitudinal alignment work during preparation work before an experiment is omitted, and the calibration steps are simplified. The whole ball screw main body can rotate 360 degrees, and meanwhile, the horn antenna on the ball screw main body is driven to rotate, so that only an object to be detected is required to be placed at the fixed position of the side face of the guide rail, and the horn antenna can perform an experiment of strip SAR imaging along with the movement of the ball screw on the rail. Through the transformation, the darkroom measuring system can better complete the following experiments:
firstly, RCS measurement. The Radar Cross Section (RCS) is an assumed area for describing the echo intensity of a target, and can be understood as a projected area of a metal ball which produces the same scattering effect as a radar target.
Prediction of RCS, whether simple or complex, has been a challenge, and testing the RSC of a target is therefore very important. Factors affecting the radar scattering cross section are: physical characteristics, namely electromagnetic characteristics, of the target to be measured; the shape and attitude of the target; various electromagnetic parameters of incident waves; the location and polarization state of the radar transmissions and receptions. The electric field of RCS is defined as:
wherein r represents the distance from the measuring radar to the object to be measured, EiAnd HiIndicating the intensity of the electromagnetic wave of the incident signal emitted from the emitting end, Es(r) and HsAnd (r) represents the electromagnetic field intensity of the echo signal measured by the collecting end. RCS is a scalar quantity, with the unit m2Usually written in logarithmic form (called decibel square meters, written as dBsm), i.e.:
σdBsm＝10lgσ(r)；
the above formula is applied to theoretically calculate the RCS value of the object. In the experiment, the data processing method for the measurement of the general target RCS is to obtain an echo signal by measurement, and then calculate the value of the target RCS by the radar distance equation. The radar range equation is as follows:
wherein, PrTo receivePower, PtFor transmit power, G is the antenna gain. In the formula except PrIn addition to σ, the value of RCS is only proportional to the received power when other parameters are unchanged. The relationship between RCS and received power is as follows:
wherein σ0To calibrate the RCS value of the target, P0The received power is used for calibrating the target measurement under the same measurement condition. In general, the present invention uses standard metal round balls or metal flat plates as calibration targets because their RCS values can be accurately determined by theoretical calculation. Sigma in the above formula0And P0For a given measurement system, the quantities are known in the same experiment, so that for any object that needs to be measured, only P is measuredrThe RCS value of the target can be converted.
In actual experimental measurement systems, however, since it is much easier to measure the output of a voltage than to directly measure the received power, the power is replaced by a voltage:
thus, after computer processing, the RCS of the target can be plotted. After the laboratory is reformed, not only the distance when measuring RCS has had more nimble selection, can be through the every single move angle of adjustment antenna loudspeaker moreover, measure the RCS value that different angles shone the object that awaits measuring. Since the object under test of the present invention will not generally be a standard metal ball or plate, it is necessary to perform RCS measurements at different pitch angles.
(2) Polarized RCS measurement. The RCS value of the target is measured depending on the polarization of the transmit and receive antennas. Any mode transmit and receive polarization can be decomposed into two mutually orthogonal polarization components, as follows:
Et＝Etvcosγt+Ethsinγt
Er＝Ervcosγr+Erhsinγr；
in the formula, EtAnd ErIs arbitrary, γtAnd gammarAngle between electric field direction and vertical direction of transmitted and received signals, Etv,Eth,ErvAnd ErhAre different components of the electric field, the indices t and r represent the transmit and receive signals, and v and h represent the vertical and horizontal polarizations. If the components of the received field are represented by field components of the incident wave, the transform coefficients form a scattering matrix:
Erv＝SvvEtv+ShvEth
Erh＝SvhEtv+ShhEth；
where each S is a complex number, the scattering matrix is a set of four dimensionless complex numbers, namely:
the relationship between the elements of the electric field scattering matrix and the elements of the RCS scattering matrix is:
σij＝|Sij|；
in both of the above two forms, the matrix consists of four complex numbers, and generally eight quantities, four amplitudes and four phases, are measured. Not all quantities are absolutely necessary, however, and first of all, the frequency phase at the radar can only be measured in a relative sense, taking into account the propagation distances of the incident and scattered waves. Second, one of the phase relationships between the four elements can be taken as a reference when there is no absolute phase alignment. Finally, cross-polarized terms (σ) due to reciprocityvhAnd σhv) Must be equal and the independent parameters are further reduced. Therefore, the necessary independent parameters to describe the radar cross-section matrix are reduced to five. After the laboratory is reformed, the angle is marked, so the method is usedObviously, more choices are provided when the polarization angle of the horn antenna is rotated, and the measurement of the polarized RCS can be better carried out.
(3) And (6) SAR imaging. The initial radar was a Real Aperture Radar (RAR), but since the imaging resolution is proportional to the aperture (i.e. length) of the radar antenna and inversely proportional to the wavelength and the observation distance, the resolution of the desired target echo signal image is higher, and only the length of the antenna can be increased, which is not practical, so that a Synthetic Aperture Radar (SAR) was invented. The synthetic aperture radar sequentially transmits and collects electromagnetic waves, and electromagnetic wave signals are digitized and then stored. This ordered arrangement of the received signals constitutes a virtual antenna that is much longer than the original antenna, since the received signals occur at different times, at different locations, which is also the reason for it being referred to as a "synthetic aperture". By way of working division, SAR imaging can be divided into a stripe mode, a beam mode and a scanning mode, and the imaging modes of the stripe mode, the beam mode and the scanning mode are shown in fig. 3. Strip SAR imaging: in the most common scanning mode, the pointing direction of the antenna is kept unchanged during working, a scanning area moves along with the platform, and antenna beams scan at a constant speed to form a scanning band. Scanning SAR: when the platform moves, the wave beam periodically scans along the distance direction, a plurality of scanning zones are provided, and the scanning area is correspondingly increased. Bunching SAR: when the platform moves, the direction of the antenna changes along with time and always points to the same area. Wherein the strip SAR imaging is an imaging mode which is a basis for comparison in the centralized imaging mode. Depending on the direction of the antenna, the strip-type SAR imaging can be divided into front-side, oblique-side and front-oblique imaging. The following introduces a most mature and classical synthetic aperture radar imaging algorithm, the range-doppler algorithm, also called RD algorithm. The RD algorithm mainly includes a distance compression process and a direction compression process, and also includes a distance migration correction process as an auxiliary process, and the algorithm flow is shown in fig. 4. The basic idea of the RD algorithm is to decouple the distance direction and the azimuth direction, and then consider the two parts as two one-dimensional processes to be completed respectively, and then introduce the two parts respectively.
(3.1) distance-wise processing of RD Algorithm
The linear frequency modulation pulse signal is the most common emission signal in the SAR imaging system, the frequency modulation signal well solves the problem that the bandwidth and the pulse width of a common pulse cannot be increased simultaneously, and the resolution ratio is improved. The complex expression of the linear frequency modulation pulse signal is as follows:
wherein the content of the first and second substances,
f0for the initial carrier frequency, τ is the signal pulse width and K is the chirp rate.
Chirp is the most commonly used signal in SAR imaging, and the process of receiving echo signals by radar can be regarded as the process of passing signals reflected by a target through a linear system, and the echo signals are related to the backscattering coefficient of an object. Therefore, the invention can write the echo signal of the target into the following form:
s(τ,ta)＝σ*h1(τ,ta)*τh2(τ)；
wherein the content of the first and second substances,
where τ is the fast time component of time t, taSlow time component of time t, convolution symbol, h1Indicating the modulation of the azimuth direction, h2The distance-wise modulation is shown. The distance-wise matching function is:
gr(τ)＝s0(-τ)exp[-jπkrτ2]；
distance-wise processed signal:
sr(τ,ta)＝σ*h1(τ,ta)*τAr(τ)；
wherein A isrAnd (tau) is an envelope of the distance processed signal, the envelope of the emission signal is different, and the envelope of the distance processed signal is changed accordingly, and is a sinc function in general.
(3.2) distance migration correction processing
The reason for the generation of the range migration is that the range component and the azimuth component of the echo signal are coupled, and decoupling, namely range migration correction processing, is needed to perform decoupling and then divide the signals into two one-dimensional signals for processing.
The distance-wise processed signal is rewritten as:
when the range migration correction is carried out, the formula is rewritten as follows:
wherein R isrefIs a reference distance that does not vary with slow time. For R (t) in the signal before rewritinga) Doing a second order Taylor expansion, the formula can be rewritten as follows:
to those in the formula
And carrying out Fourier transform of the azimuth direction to obtain an azimuth direction frequency domain signal:
(3.3) Azimuth processing of RD Algorithm
Azimuth matching function:
the processed signals are:
wherein A isa(ta) The envelope of the processing result is also typically a sinc function.
It can be known from the above description that the SAR measurement system can be regarded as a "one step one stop" mode of operation. However, the transmission and reception of signals in the movement of the antenna requires a high measurement system. Therefore, in practical experiments, experimenters often design a plurality of measuring points on the motion track of the antenna platform for measurement, which well simulates the working mode of a real antenna and also simplifies the experiments. Meanwhile, compared with a single-polarization SAR, the scattering information measured by the full-polarization SAR is more comprehensive, and the potential of the full-polarization SAR in the application fields of agriculture, oceans and the like is very large, so that SAR imaging experiments under different polarization conditions are necessary. After the laboratory is reformed transform, the ball screw that measurement system was used for fixed antenna can use self to rotate as the whole 360 degrees of axle, and the track of cooperation lead screw below can simulate the motion of airborne SAR imaging system on the airline, has realized the measurement mode of "one step one stop" receiving and dispatching signal. Due to the diversity of the polarization modes of the horn antenna, the measuring system can also meet SAR imaging experiments with different polarizations.
The technical effects of the present invention will be described in detail with reference to experiments.
The present invention modifies the experimental measurement system to solve the problems in the experimental process, and the present invention will be described in detail with reference to the actual experimental process.
(1) RCS measurement experiments.
(1.1) firstly, according to the test requirement, selecting a calibration body, and determining the frequency band, the plan state and the length of the antenna from a carrying platform of the horn antenna, wherein the invention uses VV polarization.
The step is simple in description, but is often the most time-consuming item in the practical operation process of the experiment. The reason is as follows: firstly, the loading platform is not fixed, and the shaking causes the repetition of the calibration work; secondly, the alignment process of the object carrying platform and the antenna horn not only needs to move transversely, but also needs to move longitudinally, and the calibration is difficult; thirdly, the antenna bracket is in a semi-fixed state and is easy to shake; fourthly, the height of the carrying platform is fixed. The improved implied measuring system saves the work of transverse alignment because the loading platform is aligned with the center of the antenna bracket in advance, and simplifies the operation of the alignment step because the loading platform and the flat plate for fixing the antenna horn are designed to be freely adjustable up and down.
And (1.2) measuring system connection and starting up preparation.
And selecting a matched power amplifier corresponding to the frequency range (18.5-26.5 GHz) of the antenna horn, and connecting the circuit according to the transmission line of the signal. In general, because the distance from the doorway is long and the influence of electromagnetic radiation is small, the accuracy of received signals is ensured in experimental measurement, so that a horn antenna close to the doorway is selected as a transmitting radar, and the other is a receiving radar. The sequence of wiring is as follows, the transmitting end: the spectrometer transmits signals through a port 2, is connected to an IN port of a power amplifier for preheating, is led OUT from an OUT port and is connected to a transmitting antenna. Receiving end: the line diagram is shown IN fig. 5, which is drawn from the receiving horn, to the IN port of the amplifier, and from the OUT port to the 1 port of the spectrometer. The spectrometer and the two signal amplifiers are then turned on and preheated for about 10mins to stabilize the transmitted signal and all the instruments.
And (1.3) setting parameters.
The following parameters of the spectrometer need to be set before each experimental test.
A signal receiving and transmitting line: the S21 mode is generally used, i.e., 2 port sends out signals and 1 port receives signals.
Frequency sweep range: according to the specification of the antenna horn used in the experiment, a matched sweep frequency range is selected, and the frequency range of 18.5-26.5 GHz is selected.
Scanning points: the number of scanning points is from 201 to 1001, and the more the number of scanning points is, the denser the number of obtained data points is. However, the number of scanning points is not long and good, and sometimes, the number of scanning points is too many, which may increase the difficulty of data processing, so that a proper number of scanning points should be selected, and 601 sampling points are selected in the invention.
(1.4) measuring the empty background.
This step is important when performing internal field RCS measurements, which require calibration of the electromagnetic properties of the environment. The calibration result is inaccurate, and the accuracy of the whole experiment is not high. When the empty background is measured, all objects irrelevant to the experiment in the microwave darkroom are ensured to be completely emptied, and the influence of a small object on an echo signal is huge. The order of measuring the empty background and measuring the calibration object can be changed, as long as the overall environment in the microwave darkroom is not changed in the whole experiment process.
And (1.5) measuring the calibration object.
The key to measuring the RCS value of a calibration object is to align the position of the stage and the antenna horn and then measure. This step of alignment is much simplified since the present invention pre-aligns the carrier platform and the rail. When a calibration object is measured, the environment in the microwave darkroom is ensured to be consistent with the environment for measuring the empty background in (1.4), and the influence of other factors on an echo signal is avoided.
And (1.6) measuring the target to be measured.
And similarly, under the condition of ensuring that the internal environment of the microwave darkroom is not changed, placing the target to be measured on the object stage and aligning. And transmitting a pulse signal through a frequency spectrograph, recording an echo signal, and clicking a save button after acquiring the desired data. In most experiments, the experimenter needs to measure not only the RCS value of a single angle but also the RCS value of an object to be measured at different angles, and the rotation of the carrying platform can be controlled by the computer and then the measurement is carried out. It should be noted that the measurement at different angles is different from the measurement at different pitch angles mentioned above, and here, the angle of change in the horizontal direction is used, and the pitch angle refers to the angle of change in the vertical direction.
(1.7) RCS measurement of different distances.
The measurement of RCS of different distances is required in part of experiments, so that the invention adds a guide rail to the microwave darkroom measurement system to meet the condition of RCS measurement of different distances. When RCS measurement experiments with different distances are carried out, the distance of the device is adjusted only by using the rotary worktable below the ball screw. The radar platform main body is adjusted to the position required by the invention and then fixed. During this adjustment, the other environment within the microwave darkroom remains unchanged. After the adjustment is finished, the measurement is performed according to the above (1.1) to (1.6) experimental procedures, and if measurement data at a plurality of distances is required. Experimenters can carry out the adjustment of distance under the condition that does not change loudspeaker antenna and the object state that awaits measuring, has reduced the influence. It should be noted that the length of the track of the present invention is not fixed, and the track is formed by splicing short guide rails with equal length. Therefore, if the experiment has the requirement and the condition in the microwave darkroom allows, the guide rail can be correspondingly increased in length according to the requirement, and the condition that the guide rail is fixed to cause the experiment requirement not to be met can not be generated.
(1.8) RCS measurement of different polarizations.
Through the description of the polarization state of the antenna in the technical background section, it can be known that the influence of different polarization orientations on the target echo signal is great, so that the measurement of the echo signal under different polarizations of the antenna is also essential in experiments. The invention improves the prior adjusting device and increases the angle marking. When the measurement is carried out, the adjustment is carried out only according to the angle representation marked in advance. After the polarization state of the horn antenna is adjusted, the measurement is performed according to the above experimental procedures (1.1) to (1.6).
(2) SAR imaging experiments.
In the practical application of the SAR imaging system, the radar platform is often in constant motion. The existing test system has no capability of transmitting and receiving signals during movement, so the invention adopts a 'one-step-one-stop' transmitting and receiving mode. The receiving and transmitting mode not only considers the condition of a measuring system, but also well simulates the working mode of a real synthetic aperture radar.
The antenna bracket designed by the invention can rotate integrally, and an experimenter only needs to rotate the antenna by 90 degrees to ensure that the flat plate for fixing the horn antenna is vertically parallel to the guide rail, and then places an object at a proper position on the side of the guide rail, so that the strip-type SAR imaging experiment can be realized. The SAR imaging experiment comprises the following specific steps:
and (2.1) testing the antenna performance.
When the antenna performance test is carried out, the transmitting antenna is firstly placed at the position of an object to be tested, the receiving antenna is used for simulating the motion of the radar, the antenna radiation characteristic in the azimuth direction is obtained and is used as the matched filtering function of the azimuth compression. In the above SAR imaging principle, the azimuth matched filter function is derived from the transmit signal. In practical experiments, the invention can obtain the matched filter function corresponding to the experiment through the method, and the processing of the azimuth signal by using the matched filter function is very accurate. The invention can also obtain the lobe width of the antenna emission signal from the above process, so as to determine the scanning range of the azimuth direction.
And (2.2) positioning the antenna and the target coordinate.
The linear distance of the target to the track is measured and the synthetic aperture length is determined from the antenna lobe width. The length of the synthetic aperture selected by the invention is smaller than the width of the lobe of the antenna, so that the echo signals emitted from all positions after being scattered by an object can be received by a radar. The process of determining the synthetic aperture length is also the process of determining the stopping point of the horn antenna on the track (to perform the receiving and sending operation of 'one step and one stop'), the point for receiving and sending signals is determined, and the incident angle is naturally determined.
And (2.3) setting scanning parameters.
Similarly, before the SAR imaging experiment is performed, the following parameters need to be designed:
frequency sweep range: the center frequency needs to be set first, and in order to ensure the imaging effect, the size of the target should be electrically large relative to the wavelength of the incident wave. In order to increase the range-wise resolution for displaying the structural features of the object, a bandwidth should be set as large as possible.
Sampling point number: the larger the number of sampling points, the larger the range of the distance to display. If the number of sampling points is too small, the high-resolution range images of the target are stacked, and the target cannot be completely displayed. The more the sampling number is, the more the measurement data is, and the processing is inconvenient.
Azimuth scanning range: the scan range is larger than a synthetic aperture length covering the target.
Azimuth scanning interval: the azimuth scan interval is related to the actual aperture of the antenna, and one sixth or one eighth of the antenna aperture is typically selected.
And (2.4) strip scanning.
After all preparations are made, the antenna needs to be moved along the azimuth direction according to preset measuring points, and strip SAR imaging is simulated. The measurement system will transmit signals and collect data according to the set parameters.
And (2.5) strip SAR imaging of different polarizations.
As with RCS measurements in different polarizations, the effect of different polarization orientations on the echo signal of the target is significant, and is more pronounced for SAR images formed by SAR imaging. When the experimenter carries out measurement of different polarizations, the experimenter only needs to adjust the polarization state of the horn antenna according to the experimental requirements, and then the measurement is carried out according to the steps (2.1) to (2.4).
The two experiments described above are only the basic experiments that can be realized by the present invention, and the present invention can clearly know from the above description that: when RCS measurement experiments and SAR imaging experiments are carried out, different antenna polarization states are required to be changed to obtain expected effects of the experiments, and the method marks the polarization of the horn antenna, so that the operation of changing the polarization is greatly facilitated, the precision is greatly improved, more polarization angles are selected, and the requirements of circular polarization experiments in the future can be met. When the experimental calibration work is carried out, the guide rail and the carrying platform are aligned and fixed in advance, so that the preparation time of the experiment is saved, and the accuracy is improved.
In the description of the present invention, "a plurality" means two or more unless otherwise specified; the terms "upper", "lower", "left", "right", "inner", "outer", "front", "rear", "head", "tail", and the like, indicate orientations or positional relationships that are based on the orientations or positional relationships shown in the drawings, are merely for convenience in describing and simplifying the description, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," "third," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any modification, equivalent replacement, and improvement made by those skilled in the art within the technical scope of the present invention disclosed in the present invention should be covered within the scope of the present invention.
Claims (10)
1. A multifunctional internal field scattering imaging measurement system is characterized in that the multifunctional internal field scattering imaging measurement system is provided with:
a carrier platform;
a groove fixed by a screw is additionally arranged above the carrying platform, a fixed hollow pipe is arranged above the groove, the hollow pipe is provided with an internal thread, and a support column with an external thread is arranged above the hollow pipe and supports a flat plate;
the antenna horn is fixed on a flat plate, and a connecting device is arranged behind the flat plate and used for connecting the flat plate with the ball screw;
marking the setting angle of the polarization adjusting device; a ring-ball rotary working table is arranged below the ball screw main body and connected with a track, and the track center and the carrying platform are aligned in advance.
2. The multifunctional internal field scattering imaging measurement system of claim 1, wherein the diameter of said externally threaded post is 40 mm.
3. The multifunctional internal field scattering imaging measurement system as claimed in claim 1, wherein a foam frustum is placed on said flat plate.
4. The multifunctional infield scatter imaging measurement system of claim 1, wherein the maximum limit height of the slab from the hollow tube is 320mm and the maximum height of the object from the ground is 2114 mm.
5. The multifunctional infield scatterometry imaging measurement system of claim 1, wherein the slab and the foam frustum directly above which the object is supported are serrated and bite into each other.
6. The multifunctional internal field scattering imaging measurement system as claimed in claim 1, wherein a connecting device is provided behind the plate to connect the plate with a ball screw, and the antenna horn is freely moved up and down by a motor at 1800 rpm.
7. The application of the multifunctional internal field scattering imaging measurement system as claimed in any one of claims 1 to 6 in RCS measurement experiments of different distances, which comprises:
the electric field of RCS is defined as:
wherein r represents the distance from the measuring radar to the object to be measured, EiAnd HiIndicating the intensity of the electromagnetic wave of the incident signal emitted from the emitting end, Es(r) and Hs(r) represents the echo signal electromagnetic field strength measured by the collecting end; RCS is a scalar quantity, with the unit m2Usually written in logarithmic form, called decibel square meters, and noted dBsm:
σdBsm＝10lgσ(r)；
the data processing method for target RCS measurement comprises the steps of firstly measuring to obtain an echo signal, and calculating the value of the target RCS in a reverse mode through a radar range equation, wherein the radar range equation is as follows:
wherein, PrTo receive power, PtIs the transmit power, G is the antenna gain; in the formula except PrExcept the sigma, when other parameters are unchanged, the value of RCS is only in direct proportion to the received power; the relationship between RCS and received power is as follows:
wherein σ0To calibrate the RCS value of the target, P0The method comprises the steps of measuring the received power of a calibration target under the same measurement condition; standard metal ball or metal flat plate is used as calibration target, sigma in the formula0And P0For a given measurement system, the quantities are known in the same experiment, so that for any object that needs to be measured, only P is measuredrConverting the RCS value of the target;
in practical experimental measurement systems, the power is replaced by voltage:
after computer processing, a plot of the RCS of the target is plotted.
8. The application of the multifunctional internal field scattering imaging measurement system as claimed in any one of claims 1 to 6 in RCS measurement experiments under different polarizations, which comprises:
the measured RCS value of the target is dependent on the polarization of the transmit and receive antennas, and the transmit and receive polarizations are decomposed into two mutually orthogonal polarization components as follows:
Et＝Etvcosγt+Ethsinγt
Er＝Ervcosγr+Erhsinγr；
in the formula, EtAnd ErIs arbitrary, γtAnd gammarThe included angle between the electric field direction of the transmitting and receiving signals and the vertical direction, the angle marks t and r represent the transmitting and receiving signals, and v and h represent vertical and horizontal polarization; the components of the received field are represented by field components of the incident wave, the transform coefficients constituting a scattering matrix:
Erv＝SvvEtv+ShvEth
Erh＝SvhEtv+ShhEth；
where each S is a complex number, the scattering matrix is a set of four dimensionless complex numbers:
the relationship between the elements of the electric field scattering matrix and the elements of the RCS scattering matrix is:
σij＝|Sij|；
in both of the two formulas, the matrix is composed of four complex numbers, and eight quantities, namely four amplitudes and four phases, need to be measured; firstly, the propagation distances of incident waves and scattered waves and the frequency phases at the radar can only be measured in a relative sense; secondly, when no absolute phase is adjusted, one of the phase relations among the four elements is taken as a reference; finally, the necessary individual parameters describing the radar cross-section matrix are reduced to five.
9. The application of the multifunctional internal field scattering imaging measurement system of any one of claims 1 to 6 in SAR imaging experiments under different polarizations, which comprises: decoupling the distance direction and the azimuth direction, and respectively finishing the two parts as two one-dimensional treatments; the method specifically comprises the following steps:
(1) distance direction processing of RD algorithm
The complex expression of the chirp signal is:
wherein the content of the first and second substances,
f0is an initial carrier frequency, tau is a signal pulse width, and K is a frequency modulation slope;
writing the echo signal of the target into the following form:
s(τ,ta)＝σ*h1(τ,ta)*τh2(τ)；
wherein the content of the first and second substances,
where τ is the fast time component of time t, taSlow time component of time t, convolution symbol, h1Indicating the modulation of the azimuth direction, h2Indicating a modulation of the distance direction; the distance-wise matching function is:
gr(τ)＝s0(-τ)exp[-jπkrτ2]；
distance-wise processed signal:
sr(τ,ta)＝σ*h1(τ,ta)*τAr(τ)；
wherein A isr(tau) is the envelope of the distance processed signal, the envelopes of the emission signals are different, the envelope of the distance processed signal is changed accordingly, and the distance processed signal is a sinc function;
(2) range migration correction process
Decoupling is carried out, then two one-dimensional signal processing are carried out, decoupling is obtained, and range migration correction processing is carried out;
the distance-wise processed signal is rewritten as:
when the range migration correction is carried out, the formula is rewritten as follows:
wherein R isrefFor reference distances that do not vary with slow time, R (t) in the signal before overwritinga) Doing a second-order Taylor expansion, then the formula is rewritten again as follows:
to pair
Carrying out Fourier transform of the azimuth direction to obtain an azimuth direction frequency domain signal:
(3) orientation processing of the RD algorithm:
azimuth matching function:
the processed signals are:
wherein A isa(ta) Is a sinc function to process the envelope of the result.
10. An electromagnetic wave measuring system in a microwave darkroom, which is characterized in that the multifunctional internal field scattering imaging measuring system of any one of claims 1 to 6 is used in the electromagnetic wave measuring system in the microwave darkroom.
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| CN115453214A (en) * | 2022-08-23 | 2022-12-09 | 西安电子科技大学 | Measuring device and measuring method for internal field active interference scattering characteristics |
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| CN115079112B (en) * | 2022-07-21 | 2022-12-20 | 中国航发四川燃气涡轮研究院 | Test system and test method for near-earth dynamic RCS (Radar Cross section) test of aero-engine |
| CN115453214A (en) * | 2022-08-23 | 2022-12-09 | 西安电子科技大学 | Measuring device and measuring method for internal field active interference scattering characteristics |
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