CN102768310B - Method for eliminating multipath interference in antenna test environment by adopting distance offset technology - Google Patents

Abstract

The invention relates to a method for eliminating the multipath interference in an antenna test environment by adopting a distance offset technology. A relation between a direct signal in the antenna test environment and a multipath interference signal is analyzed, two frequency responses in different test distances are tested and the distance offset technology is adopted to separate the direct signal from the frequency responses, so that the influence of the multipath interference on the antenna test can be eliminated and more accurate antenna test data is obtained. The method is particularly effective for a high gain and low minor lobe antenna.

Description

Adopt ranging offset technology to subdue the method that in antenna measurement environment, multipath disturbs

Technical field

The invention belongs to antenna measurement field, be specifically related to one and utilize ranging offset technology in antenna measurement environment, to eliminate multipath undesired signal, improve the using method of measuring antenna parameter (comprising directional diagram and gain and other parameter) precision.

Background technology

Weigh the actual emanations performance of one pair of antenna, need to measure by accurate.In test environment, (microwave dark room or open area test site) exists multipath to disturb, and in conventional frequency domain measurement, minor level is raised in the strong reflection meeting that main lobe wave beam forms in the time of toward side wall; In the time that the performance of absorbing material is not ideal enough, can have a strong impact on measuring accuracy from the multipath undesired signal of sidewall, rear wall.

In microwave dark room, along with the reduction of test frequency range, the multipath reflection of sidewall strengthens, and causes the measuring accuracy of antenna radiation pattern to be difficult to reach ± 1dB; The following frequency range of 100MHz deteriorates into ± and more than 2dB.In the time of field testing, uncontrollable due to external environment condition, multipath disturbs more serious.More serious for high-gain, low sidelobe antenna situation.

Summary of the invention

Based on above situation, the present invention proposes one and utilizes measuring distance migration technology, eliminates multipath and disturbs the impact on test result.The frequency domain response obtaining due to Antenna testing system is that the vector of direct signal and multipath undesired signal is synthetic, corresponding by testing twice frequency domain under different measuring distances, can by direct-path signal and the wavelength-division of multipath undesired signal from, obtain frequency domain response separately, reach and eliminate the object that multipath disturbs.

Technical scheme

Step 1: build Antenna testing system, the tested antenna of the auxiliary antenna of transmitting terminal and test lead is positioned at sustained height, and is positioned at same axis;

Step 2: according to tested antenna working frequency range, test start-stop frequency and the frequency interval Δ f of vector network analyzer is set, Δ f should be less than 10MHz, suggestion is placed in 1MHz.

A: in the time that measuring distance is d, the frequency domain response of Antenna testing system is S ' ₂₁;

B: (Δ d d and Δ d < λ in the time that measuring distance is d+ Δ d _min), the frequency domain response of Antenna testing system is S " ₂₁;

Step 3: the Interference Model of setting up direct-path signal and multipath interference wave:

Wherein, | (S ₂₁) the d| amplitude that is direct-path signal, for the phase place of direct-path signal, | (S ₂₁) _r| be the amplitude of multipath undesired signal, for the phase place of multipath undesired signal; Transitive relation by signal in Antenna testing system can obtain:

In formula:

G _t: the gain of emitting antenna;

G _r: the gain of receiving antenna;

: the direction of an electric field figure of receiving antenna;

L ₁(f), L ₂(f): be respectively the loss that connects auxiliary antenna, tested antenna cable in Antenna testing system;

λ: the wavelength of the output signal of test macro;

R: the distance of multipath;

D: the distance of auxiliary antenna and tested antenna;

α: the angle of multipath interference and direct wave.

Step 4: because twice distance test is very little apart from changing, its frequency domain response amplitude changes very little, can be approximated to be: (S ' ₂₁(f)) _d≈ (S " ₂₁(f)) _d=a, (S " ₂₁(f)) _r≈ (S " ₂₁(f)) _r=b, therefore the frequency domain response of twice test in front and back can be expressed as

In formula: the range difference of multipath in twice measurement of Δ r; A, b is constant; S ' ₂₁(f), S " ₂₁(f) obtained by step (2) test.

Due to $\mathrm{\&Delta;r}=\frac{d}{r}\mathrm{\&Delta;d},$ Obtain:

Substitution (2) formula is by can be calculated:

The mathematic(al) representation of multipath signal is:

The mathematic(al) representation of direct signal is:

Step 5: in order to obtain formula (2), the wave-path r of multipath undesired signal in (3), first supposes that its distance is in formula: the tested antenna axis of the auxiliary antenna that w is reflection end and test lead and the distance of darkroom sidewall.Can obtain:

In formula: for multipath is r ₀time i the phase-shift value that frequency is tried to achieve by (3) formula;

ε _rfor cable l ₁, l ₂specific inductive capacity;

Step 6: right the true value to multipath being averaging multipath distance substitution formula (4) can be in the hope of the frequency domain analog value of direct signal.

Beneficial effect

By the relation between direct signal and multipath undesired signal in analysis antenna measurement environment, adopt ranging offset technology, direct signal is separated from frequency domain response, disturb the impact on antenna measurement thereby can subdue multipath, obtain more accurate antenna measurement data.Especially particularly effective to high-gain, low sidelobe antenna.

Brief description of the drawings

Fig. 1 is that in the inventive method, the interior multipath of microwave dark room disturbs schematic diagram.

Fig. 2 is the ranging offset method schematic diagram in the inventive method.

Fig. 3 is the experimental result picture in the inventive method.

Embodiment

Now in conjunction with implementation step, accompanying drawing, the invention will be further described:

1) while measuring antenna in microwave dark room, also include multipath and disturb in frequency domain response except direct signal, making the air line distance between dual-mode antenna is d, and it is r that multipath disturbs the distance of process.The amplitude of direct-path signal is the phase place of direct signal is the attenuation coefficient of absorbing material is Г (being less than 1 plural number), and the amplitude that in frequency domain response, multipath disturbs is the phase place that multipath disturbs is therefore direct signal and the multipath that can set up in the antenna measurement system in microwave dark room disturb unified model, and its mathematic(al) representation is: wherein, G _tfor the gain coefficient of emitting antenna in greatest irradiation direction, G _rfor the gain on the maximum receive direction of receiving antenna, for normalized power pattern, wherein for spherical coordinates position angle, θ is surface level angle, for the angle of pitch, λ is free space signal wavelength, L ₁for the loss of cable 1, L ₂for the loss of cable 2, l ₁for the length of cable 1, l ₂for the length of cable 2, ε _rfor cable specific inductive capacity, for the remaining time delay being caused by measuring system, for the phase shift of reflection spot attenuation coefficient.

2) in the time that measuring distance is d, order (A is only relevant with test frequency, systematic parameter, antenna radiation pattern, irrelevant with measuring distance), in frequency domain response, the amplitude of direct signal can be expressed as order (B and measuring distance are irrelevant), the amplitude that in frequency domain response, multipath disturbs can be expressed as therefore the frequency response of system is

3) next (Δ d d and Δ d < λ in the time that measuring distance is d+ Δ d _min), multipath disturbs the distance of process to become r+ Δ r, by step 2) can obtain, the frequency domain response of test macro is:

4) frequency domain response of twice measurement before and after analysis, its amplitude change amount is very little, can be similar to and think $\sqrt{\frac{A}{{(d+\mathrm{\&Delta;d})}^2}}\&ap;\sqrt{\frac{A}{d^2}}=a,\sqrt{\frac{B}{{(r+\mathrm{\&Delta;r})}^2}}\&ap;\sqrt{\frac{B}{r^2}}=b,$ Therefore the frequency domain response of twice test in front and back can be expressed as with with reference to Fig. 2, can be obtained by geometric relationship: r asks local derviation to d, has bring into ? isolate multipath signal, the mathematic(al) representation of multipath signal is: ? bring into obtain direct signal, the mathematic(al) representation of direct signal is:

5) said method is verified: choose the tested antenna of half-wave dipole that one pair of frequency of operation is 300MHz, it is installed on to size is that (in H (m) microwave dark room, it is tested, auxiliary antenna is UPA6109 in 25 (L) × 15 (W) × 15.Test frequency is the antenna radiation pattern of 300MHz.The range difference Δ d that is known twice test by analysis above should be much smaller than apart from d, and for fear of there is phase ambiguity, requires Δ d to be less than minimum wavelength λ _min, swept frequency range is 100M～500M, easily knows corresponding λ _minfor 0.6m, be 0.25m therefore Δ d is set, measuring distance is 18.25m for the second time.Multipath r is 25.37m.To step 4), can obtain the directional diagram of multipath signal before and after separating from direct-path signal, according to step 1) shown in Fig. 3.Can find, the directional diagram after separation and reference direction figure have identical preferably, and this method is effective.

Claims (2)

1. adopt ranging offset technology to subdue the method that in antenna measurement environment, multipath disturbs, it is characterized in that step is as follows:

Step 1: build Antenna testing system: the tested antenna of the auxiliary antenna of transmitting terminal and test lead is positioned at sustained height, and be positioned at same axis;

Step 2: according to tested antenna working frequency range, test start-stop frequency and the frequency interval Δ f of vector network analyzer is set, Δ f is less than 10MHz;

A: in the time that measuring distance is d, the frequency domain response of Antenna testing system is S ₂₁';

B: in the time that measuring distance is d+ Δ d, the frequency domain response of Antenna testing system is S ₂₁";

Step 3: the Interference Model of setting up direct-path signal and multipath interference wave: wherein, | (S ₂₁) _d| be the amplitude of direct-path signal, for the phase place of direct-path signal, | (S ₂₁) _r| be the amplitude of multipath undesired signal, for the phase place of multipath undesired signal; Transitive relation by signal in Antenna testing system obtains:

In formula:

G _t: the gain of emitting antenna;

G _r: the gain of receiving antenna;

normalized power pattern, wherein for spherical coordinates position angle, θ is surface level angle, for the angle of pitch;

L ₁(f), L ₂(f): be respectively the loss that connects auxiliary antenna, tested antenna cable in Antenna testing system;

λ: the wavelength of the output signal of test macro;

R: the distance of multipath;

D: the distance of auxiliary antenna and tested antenna;

α: the angle of multipath interference and direct wave;

Г: the attenuation coefficient of absorbing material;

Step 4: the frequency domain response of twice measurement before and after analyzing, its amplitude change amount is very little, can be similar to and think $\sqrt{\frac{A}{{(d+\mathrm{\&Delta;d})}^2}}\&ap;\sqrt{\frac{A}{d^2}}=a,$ $\sqrt{\frac{B}{{(r+\mathrm{\&Delta;r})}^2}}\&ap;\sqrt{\frac{B}{r^2}}=b,$ therefore the frequency domain response of twice test in front and back can be expressed as

In formula: the range difference of multipath in twice measurement of Δ r; A, b is constant; S ₂₁' (f), S ₂₁" (f) obtained by step 2 test;

Due to $\mathrm{\&Delta;r}=\frac{d}{r}\mathrm{\&Delta;d},$ Obtain:

Substitution (2) formula is by can be calculated:

The expression formula of multipath signal is:

The mathematic(al) representation of direct signal is:

Step 5 calculating formula (2), the wave-path r of multipath undesired signal in (3): first suppose that its distance is in formula: the tested antenna axis of the auxiliary antenna that w is reflection end and test lead and the distance of darkroom sidewall, can obtain:

In formula: for multipath is r ₀time i the phase-shift value that frequency is tried to achieve by (3) formula; l ₁, l ₂for connecting respectively the cable length of auxiliary antenna, tested antenna, ε _rfor connecting auxiliary antenna cable, connect the specific inductive capacity of tested antenna cable;

Step 6: right the true value to multipath being averaging multipath distance substitution formula (4) can be in the hope of the frequency domain response value of direct signal.

2. adopt according to claim 1 ranging offset technology to subdue the method that in antenna measurement environment, multipath disturbs, it is characterized in that: described start-stop frequency and frequency interval Δ f are 1MHz.