CN115275545A - Compact absorption type filtering power divider - Google Patents
Compact absorption type filtering power divider Download PDFInfo
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Abstract
The invention discloses a compact absorption type filtering power divider, which comprises a filtering power divider and an absorption branch loaded at an input end, wherein the filtering power divider comprises two band-pass filters with a three-wire coupling structure and a composite T-shaped network between the two band-pass filters, and the composite T-shaped network comprises two symmetrical isolation resistors and a first quarter-wavelength short-circuit branch loaded between the two isolation resistors. The design based on the three-wire coupling structure provides broadband filter response, and a quarter-wavelength short-circuit branch loaded at the tail end of an output coupling feeder line of the broadband filter response brings higher passband selectivity, and the response bandwidth and the zero position can be flexibly adjusted. The composite T-shaped network is multiplexed into the absorption branches while meeting the isolation level, has the dual characteristics of isolation and absorption, and effectively reduces the use of the absorption branches. The finally designed compact absorption type filtering power divider has good absorption performance, high filtering performance, good isolation level and compact circuit size.
Description
Technical Field
The invention relates to the technical field of wireless communication, in particular to a compact absorption type filtering power divider.
Background
With the continuous development of industrial automation and intelligence, higher requirements are put on the aspects of high performance, stability and reliability of the communication system. Absorptive and non-reflective filters have attracted attention in recent years to meet the robust operation of the entire rf system. It is known that the reflected signal of a conventional reflection filter passes through sensitive non-linear components such as mixers and amplifiers, which may cause the operation state of the adjacent active stage to deteriorate. Unlike conventional reflection filters, absorption and non-reflection filters are capable of absorbing out-of-band interference signals that are reflected back to the source. Therefore, the signal-to-noise ratio and the stability of the adjacent active circuit in the radio frequency front-end system can be effectively improved.
Meanwhile, a large number of passive devices occupy a large area in a limited radio frequency front end system, and the continuous development of the modern radio frequency and microwave industries makes the demands for miniaturization, low loss and low cost more and more. Therefore, many multifunctional devices such as a filtering combiner, a filtering balun, a filtering power divider, etc. are attracting attention. The filtering power divider is a key device integrating two functions of filtering and power dividing and is widely applied to a transmitter system. Radio frequency signals generated after the intermediate frequency signals and the local oscillator signals are mixed by the mixer are divided into two paths of signals through the filtering power divider and the amplifiers, usually, in order to relieve the interference of out-of-band reflected signals, an extra isolator needs to be added between the amplifying circuit and the antenna, and the traditional method can cause the problems of large size, high loss and the like. If the filtering power divider is replaced by the absorption-type filtering power divider, the interference signal reflected outside the band can be dissipated inside the absorption-type filtering power divider, so that the inter-stage disturbance caused by the reflection of the interference signal back to the mixer is avoided, and the originally required isolator can be replaced. Therefore, it is necessary to research an absorption-type filtering power divider integrating three functions of filtering, power dividing and absorption, and the absorption-type filtering power divider can simultaneously meet the requirements of high stability, miniaturization, low loss and low cost.
As a common design method for implementing a filtering power divider, a design principle of cascading a band-pass filter and a power divider is commonly used in the design of an absorption-type filtering power divider, and the out-of-band reflected energy is usually absorbed by an absorption band stop section loading a termination load at a port. Meanwhile, a non-reflection band-pass filter with absorption performance usually adopts a topological structure based on a complementary duplexer, and in order to improve the designed filtering performance, a cascaded multi-order band-pass resonance unit is usually selected and partially connected with a multi-order absorption band-stop network in parallel, so that the designed size is too large and the loss is large. Not only does this result in a limited absorption bandwidth of the design due to the imperfect matching of the bandpass and absorptive bandstop portions. In addition, in order to achieve good absorption properties, a plurality of absorption branches are generally required. However, the multiple absorption branches not only result in larger circuit size, but also cause severe passband malformations.
Disclosure of Invention
The present invention is directed to solve the above-mentioned deficiencies in the prior art, and to provide a compact absorption filter power divider, where the proposed composite T-shaped network has dual characteristics of isolation and absorption, effectively reduces the usage of absorption branches, and implements a high-performance and miniaturized absorption filter power divider design.
In order to achieve the purpose of the invention, the invention provides a compact absorption-type filter power divider, which is composed of an upper metal strip layer, a lower metal ground layer and a middle medium substrate layer, wherein the filter power divider and an absorption branch node loaded at the input end of the filter power divider are arranged on the upper metal strip layer. Specifically, the compact absorption-type filtering power divider comprises a filtering power divider, an absorption branch loaded at the input end of the filtering power divider, an input port and two output ports, and is characterized in that: the filtering power divider comprises two band-pass filters with three-wire coupling structures and a composite T-shaped network arranged between the input ends of the two band-pass filters, wherein the composite T-shaped network comprises two symmetrical isolation resistors arranged between the input ends of the two band-pass filters and a first quarter-wavelength short-circuit branch loaded between the two isolation resistors.
Wherein the band pass filter of the three-wire coupling structure includes: the quarter-wavelength input coupling feeder line and the quarter-wavelength output coupling feeder line are arranged on the left side and the right side of the quarter-wavelength central short circuit branch in parallel and symmetrically, the first end of the quarter-wavelength input coupling feeder line of the two band-pass filters is connected with the input port, and the second end of the quarter-wavelength input coupling feeder line of the two band-pass filters is connected with the composite T-shaped network; the first ends of the quarter-wavelength output coupling feeders of the two band-pass filters are respectively connected with the two output ports, and the second ends of the quarter-wavelength output coupling feeders of the two band-pass filters are respectively loaded with second quarter-wavelength short-circuit branches.
The compact absorption type filtering power divider can be used for realizing the absorption type filtering power divider, wherein the overall circuit can be formed by an integrated filtering power divider part and an absorption branch node loaded at the input end. The integrated filtering power divider part is composed of a band-pass filter based on a three-wire coupling structure and a composite T-shaped network. The port of the band-pass filter based on the three-wire coupling structure is loaded with a quarter-wavelength short-circuit branch (Z c ) And wherein the coupled three lines are symmetrical structures, and the width of the three lines is allw 0 The distance between two adjacent lines iss. The compound T-shaped network consists of two symmetrically distributed resistors (R b ) And a quarter-wave short-circuit stub loaded in the center thereof (Z b ) And (4) forming. It can be used as an isolation network and also can be reused as an absorption branch, thereby showing the isolationThe dual properties of absorption and dissociation. The absorption branch loaded at the input end is composed of an absorption electrode (R a ) And a quarter-wave short-circuit branch (c)Z a ) And (4) forming.
For this, a stepwise deductive analysis method was employed.
(1) Firstly, for the use of common isolation resistors and no load branches (Z c ) The integrated filter power divider part adopts an odd-even mode analysis method, gives a six-port impedance matrix of the three-wire coupling structure, considers the cross coupling between two non-adjacent wires of the three-wire coupling structure, and introduces variables for accurately fitting frequency responsek cc And is characterized by the ratio of the coupling coefficient of the non-adjacent two lines to the coupling coefficient between the adjacent two lines. The port condition can be obtained by the even-mode half-cut equivalent circuit, and the reflection coefficient (& gtY & lt & gt) of the input port during the even-mode excitation can be obtained by substituting the port condition and formula conversion calculationS e 11 |), reflection coefficient of output port (# |)S e 22| and the use of ordinary isolation resistors and no load stubs | (Z c ) Transmission coefficient (& gtLiquid & ltLiquid & gt) of integrated filter power dividerS e 21 |) is used. Under odd mode excitation, the equivalent circuit can be viewed as a port circuit with only output port, whereby the input impedance through the input port: (Zoin) To calculate the reflection coefficient (. Gamma.) (Y) of output port under odd-mode excitationS o22 |). Finally, the result of the odd-even mode analysis calculation is combined to obtain the reflection coefficient (#) of the input port of the whole circuitS 11 |), transmission coefficient of the overall circuit ([ calculation of ] AS 21 |), reflection coefficient of output port (#)S 22 |) and isolation coefficient between output ports (#)S 23 |) and a frequency response curve can be obtained. The band-pass filter with compact three-wire coupling structure can generate three transmission poles and two out-of-band transmission zeros by changing the line width of three wiresw 0 And the spacing of adjacent linessThe required bandwidth can be adjusted at will, and due to the generation of three transmission poles in the band, a compact three-wire coupling structure can be obtained, and the design of the broadband is easy to realize.
(2)Secondly, the common isolation resistor is adopted and no branch is loaded (Z c ) The tail end of an output coupling feeder line of the integrated filtering power divider is loaded with a short-circuit branch section (a) of a quarter wavelengthZ c ) And forming the improved filtering power divider. The transmission coefficient (& gtnon & ltcalculation & gt) can be obtained through calculation and derivation of a theoretical formulaS 21 I) curve of change, from which it can be seen that the common isolation resistor is used and the load branch(s) ((ii)Z c ) Improved filtering power divider with changeable bandwidth and zero pointZ c And the control is easy, and better selectivity is shown.
(3) Further, on the basis of the improved filtering power divider, an isolation resistor (C) is connected with the tail end of the input coupling feeder lineR) Split into 2 new isolation resistors (R b ) And in the center thereof is loaded with a branch (Z b ) Thus forming a composite T-shaped network. The same theoretical formula is adopted to calculate and derive a method to obtain a frequency response curve of an improved filtering power divider with a composite T-shaped network, namely an absorption filtering power divider I. Compared with the improved filtering power divider adopting the common isolation resistor, the absorption type filtering power divider I can generate absorption characteristics under the condition of ensuring a certain isolation level due to the adoption of the special composite T-shaped network. Therefore, the proposed T-shaped network can be reused as an absorption branch node while being used as an isolation network, so that dual characteristics of isolation and absorption are generated. The input non-reflection performance can be viewed as the matching performance of the in-band and out-of-band inputs. Therefore, the in-band maximum reflectance is determined for a more intuitive evaluation of the absorption levelRP max And out-of-band maximum reflection coefficientRS max Smaller values thereof represent better absorption properties. The analysis can be used to obtain the result,R b = 150 ΩRS max The smallest, i.e. the best absorption properties. Defining an offset frequency Delta by comprehensively considering the matching performance of the output ports and the isolation level between the output portsf= 0.6GHz at the center frequency by integrated analysisf 0 And at frequencyf 0 ±ΔfAt the output portHas a reflection coefficient ofS 22 Inf 0 Is treated withf 0 – Δf，f 0 + Δf]Isolation coefficient between output ports in frequency rangeS 23 |，R b Set to 150 omega. In addition to this, the short-circuit branch impedance loaded in the center of T-shaped networkZ b Is also a critical parameter affecting the absorption performance of the circuit byRP max AndRS max the change curve of the pressure sensor can be known,Z b is a key parameter to achieve a good in-band and out-of-band matching performance tradeoff.
(4) Finally, in order to further improve the input non-reflection performance, a section of absorption branch knot is parallelly loaded at the input port of the absorption type filtering power divider I, and the final absorption type filtering power divider II with good input non-reflection performance is formed. Wherein the absorption branch is composed of an absorption resistorR a And a quarter-wave short-circuit branchZ a And (4) forming. And similarly, an odd-even mode analysis method can be adopted for the absorption type filtering power divider II, a frequency response curve of the absorption type filtering power divider II is obtained through calculation and deduction of an impedance matrix, and the frequency response curve is compared with the absorption type filtering power divider I without loaded absorption branches. It can be obviously seen that the input non-reflection performance of the circuit is greatly improved with the absorption branch loaded by the input port. By pairsZ a Can be obtained when the parameter scan curveZ a The input no-reflection/absorption performance is greatly improved. At the same time, withZ a Reduction of the width of the branch linew a Will also increase continuously, so chooseZ a And = 38 Ω for demonstration. At the same time, byR a The out-of-band matching performance, i.e. the out-of-band absorption performance, can be known through the parameter scanning curveR a And (4) independently adjusting. And by being different inR a Is as followsRP max AndRS max the change curve can be known, and the change curve,R a = 50 ΩRS max And taking the minimum value, namely the out-of-band absorption performance is optimal at the moment.
By combining all the analyses, the evolution process of the whole circuit structure can be clearly known, and finally, a section of matching branch is added to the input port to improve the matching performance of each port, and the parameters are optimized to obtain the final circuit.
The invention has the following innovation points:
1. the composite T-shaped network is adopted to replace a common isolation resistor, and the structure can be multiplexed into an absorption branch while meeting the isolation level, so that the isolation and absorption dual characteristics are achieved, and the circuit size is reduced. And the use of the absorption branch is reduced due to the characteristic, and the good input reflection-free characteristic can be realized only by one additional absorption branch, so that the serious distortion of the pass band is avoided.
2. The input reflection-free performance can be independently regulated and controlled by the absorption branch loaded on the input port, and the filtering performance is not influenced.
3. The design method of the integrated filtering power divider based on the three-wire coupling structure greatly reduces the circuit size, and the design bandwidth and the zero point can be arbitrarily regulated and controlled by a short-circuit branch loaded at the tail end of the output coupling feeder line.
The invention has the following beneficial effects:
for passband frequency response, broadband filter response is provided based on the design of a three-wire coupling structure, higher passband selectivity is brought by a quarter-wavelength short-circuit branch loaded at the tail end of an output coupling feeder line of the broadband filter, and response bandwidth and zero point position can be flexibly adjusted. The input non-reflection performance can be independently regulated and controlled by the absorption branch loaded by the input port. The design method of the integrated filtering power divider is adopted, the dual multiplexing characteristics of the proposed composite T-shaped network are utilized, the circuit size is greatly reduced, the loss and the cost are reduced, and the design of the miniaturized input reflection-free filtering power divider is realized. The finally designed compact absorption type filtering power divider has good absorption performance, high filtering performance, good isolation level and compact circuit size.
Drawings
The invention will be further described with reference to the accompanying drawings;
fig. 1 is a schematic structural diagram of an absorption-type filtering power divider (absorption-type filtering power divider ii) according to an embodiment of the present invention.
Fig. 2-1 is a schematic diagram of a half-cut-coupled-mode equivalent circuit structure of the compact absorption-type filtering power divider of the present invention.
Fig. 2-2 is a schematic diagram of a half-cut odd-mode equivalent circuit structure of the compact absorption filter power divider of the present invention.
FIG. 3 shows the compact absorption filter power divider of the present invention with the absorption branches (C) loaded at the input end removedR a ；Z a ，θ a ) And the input coupling feeder is connected with the improved filter power divider of a common isolation resistor (R).
Fig. 4 is a specific structural diagram of a three-wire coupling structure adopted by the compact absorption filter power divider of the present invention.
FIG. 5-1 shows the compact absorption filter power divider of the present invention for removing the absorption branch node(s) loaded at the input endR a ；Z a ，θ a ) A quarter-wave short-circuit branch at the end of the output coupling feeder line (a)Z c ，θ c ) And common isolation resistor(s) is (are) between the input coupling feed linesR) The structural schematic diagram of the half-cut-and-couple mode equivalent circuit of the original filtering power divider.
FIG. 5-2 shows the compact absorption filter power divider of the present invention for removing the absorption branch node(s) loaded at the input endR a ；Z a ，θ a ) A quarter-wave short-circuit branch at the end of the output coupling feeder line (a)Z c ，θ c ) And common isolation resistor(s) is (are) between the input coupling feed linesR) The half-cut odd-mode equivalent circuit structure schematic diagram of the original filtering power divider.
FIG. 6 shows the compact absorption filter power divider of the present invention with the absorption branch node(s) loaded at the input end removedR a ；Z a ，θ a ) A quarter-wave short-circuit branch at the end of the output coupling feeder line (a)Z c ，θ c ) And common isolation resistor(s) is (are) between the input coupling feed linesR) The frequency response curve of the original filtered power divider.
FIG. 7 shows the compact absorption filter power divider of the present invention with the absorption branch node(s) loaded at the input end removedR a ；Z a ，θ a ) A quarter-wave short-circuit branch (C) at the end of the output coupling feed lineZ c ，θ c ) And common isolation resistor(s) is (are) between the input coupling feed linesR) The 1-dB relative bandwidth of the original filtering power divider has a variation curve under different s and w0 conditions.
FIG. 8 shows the compact absorption filter power divider of the present invention with the absorption branch node(s) loaded at the input end removedR a ；Z a ，θ a ) And common isolation resistor(s) is (are) between the input coupling feed linesR) Difference of original filtering power dividerZ c The change curve of the transmission coefficient thereof.
FIG. 9 shows an absorption filter power divider I (the compact absorption filter power divider of the present invention removes the absorption branch node loaded at the input end: (R a ；Z a ，θ a ) And will isolate the resistance (a), (b)R) Converted into a composite T-network).
FIG. 10-1 shows transmission coefficients (#) of an absorption filter power divider I and an improved filter power divider as shown in FIG. 3S 21 |) and input-end reflection coefficient (& ltS 11 | from the table).
FIG. 10-2 is a graph showing the isolation coefficients (& lty & gt) of an absorption filter power divider I and an improved filter power divider as shown in FIG. 3S 23 |) and output end reflection coefficient (& lt & gtluminance & gtS 22 | to a comparison graph.
FIG. 11-1 shows the difference between the absorption type filtering power divider IR b Lower partRP max AndRS max the change curve of (2).
FIG. 11-2 shows the difference between the absorption filter power divider IR b The matching performance and the isolation level of the lower output port.
FIG. 12 shows the difference between the absorption type filtering power divider IZ b Lower partRP max AndRS max the change curve of (2).
FIG. 13-1 shows the transmission coefficients (#) of the compact absorption filter power divider (absorption filter power divider II) and the absorption filter power divider I shown in FIG. 8S 21 | and input-end reflection coefficient (& lt & gt)S 11 | from the table).
FIG. 13-2 shows the isolation coefficients (#) of the compact absorption filter power divider (absorption filter power divider II) of the present invention from the absorption filter power divider I shown in FIG. 8S 23 | and output-end reflection coefficient (& ltcalculation & gt)S 22 | from the table).
FIG. 14-1 is a schematic diagram of a compact absorption filter power divider (absorption filter power divider II) of the present invention with transmission coefficients (& gtLily) in different ZaS 21 | and input-end reflection coefficient (& lt & gt)S 11 |) change curve.
FIG. 14-2 is a schematic diagram of a compact absorption filter power divider (absorption filter power divider II) of the present invention with transmission coefficients ([ mu ] y) in different RaS 21 |) and input-end reflection coefficient (& ltS 11 |) change curve.
FIG. 15 shows a compact absorption filter power divider (absorption filter power divider II) according to the present inventionR a Lower partRP max AndRS max the change curve of (2).
Fig. 16 is a top perspective view of the compact absorption filter power divider of the present invention (absorption filter power divider ii).
FIG. 17-1 is a schematic diagram of transmission coefficients (& gtnon & lty & gt) of a compact absorption filter power divider (absorption filter power divider II) of the present inventionS 21 |) and input-end reflection coefficient (& ltS 11 |) simulation results and test results are compared.
FIG. 17-2 is a schematic diagram of the isolation coefficients (#) of the compact absorption filter power divider (absorption filter power divider II) of the present inventionS 23 |) and output end reflection coefficient (& lt & gtluminance & gtS 22 |) simulation results and test results are compared.
Detailed Description
The invention is further described with reference to the following figures and specific examples.
For a more clear understanding of the technical features, objects, and effects of the present invention, embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
Fig. 16 is a top perspective view of a compact absorption filter power divider embodying the present invention, i.e., absorption filter power divider ii. The compact absorption type filtering power divider comprises a filtering power divider, an absorption branch loaded at the input end of the filtering power divider, an input port S1 and two output ports S2 and S3. The filtering power divider comprises two band-pass filters with three-wire coupling structures and a composite T-shaped network arranged between the input ends of the two band-pass filters, wherein the composite T-shaped network comprises two symmetrical isolation resistors 8 and 8 'arranged between the input ends of the two band-pass filters and a first quarter-wavelength short-circuit branch 9 loaded between the two isolation resistors 8 and 8'. In order to further easily control the bandwidth and the zero point of the filtering power divider to show better selectivity, in the embodiment, the output side of the band-pass filter of the three-wire coupling structure is loaded with the second quarter-wavelength short-circuit branches 7 and 7'.
As shown in fig. 16, the bandpass filter of the three-wire coupling structure includes: quarter-wavelength input coupling feeders 4, 4 'and quarter-wavelength output coupling feeders 5, 5' which are parallel to and symmetrically arranged at the left and right sides of the quarter-wavelength central short-circuit branches 6, 6 'and the quarter-wavelength central short-circuit branches 6, 6', first ends of the quarter-wavelength input coupling feeders 4, 4 'of the two band-pass filters are connected with the input port S1, and second ends of the quarter-wavelength input coupling feeders 4, 4' of the two band-pass filters are connected with the composite T-shaped network; the first ends of the quarter-wavelength output coupling feeders 5, 5' of the two band-pass filters are respectively connected with the two output ports S2, S3, and the second ends of the quarter-wavelength output coupling feeders 5, 5' of the two band-pass filters are respectively loaded with the second quarter-wavelength short-circuit branches 7, 7'. The absorption branch is a third quarter-wavelength short-circuit branch 11 loaded on the input port S1 through an absorption resistor 10, the input port S1 is connected with quarter-wavelength input coupling feeders 4 and 4' of the two band-pass filters sequentially through a transmission line input line 1 and an input end impedance matching line 2, and the output ports S2 and S3 are connected with quarter-wavelength output coupling feeders 5 and 5' through output end transmission lines 3 and 3', respectively. The input transmission line 1 and the output transmission lines 3, 3' are both 50 Ω transmission lines.
In this embodiment, the first quarter-wavelength short-circuit stub 9 is short-circuited to ground through the first metalized via 15; the second quarter-wave short-circuit branches 7 and 7 'are short-circuited and grounded through second metalized through holes 13 and 13'; the third quarter-wave short-circuited stub 11 is short-circuited to ground via a third metallized via 14.
The embodiment of the invention optimizes the sizes of all parts of the filter, and the specific parameters of the filter are shown in the following table:
| parameter(s) | l p1 | l p2 | l p3 | l a | l b | l c | l 0 |
| Value (mm) | 5 | 17.6 | 10.5 | 18.9 | 18.81 | 20.72 | 19.5 |
| Parameter(s) | w p1 | w p2 | w a | w b | w c | w 0 | s |
| Value (mm) | 1.78 | 2.72 | 2.75 | 1.89 | 0.2 | 0.2 | 0.2 |
In the table, the number of the first and second,l p1 andl p3 the lengths of the input and output ports 50 omega microstrip lines respectively,w p1 for the width of the input-output port 50 omega microstrip line,l p2 andw p2 the length and the width of the input end quarter-wavelength matching branch are respectively,l a andw a the length and the width of the quarter-wave short-circuit branch loaded on the input end are respectively,l b andw b are respectively provided withThe length and width of the quarter-wave short-circuit branch loaded for the center of the composite T-shaped network,l c andw c for the length and width of the quarter-wave short-circuit stub of the out-coupling feeder terminal load,w 0 in order to couple the width of the three wires,sis the distance between two adjacent coupling lines. The substrate used in the design is RogersRO4003CHaving a dielectric constant ofε r Thickness of = 3.55hLoss tangent of 0.813mm is tanδ= 2.7×10 -3 And the thickness of the metal strip of the upper layer and the lower layer is t =0.035mm.
The design, analysis process and effect of the present invention will be described in detail with reference to the accompanying drawings.
Fig. 1 shows a schematic structural diagram of a compact absorption-type filtering power divider (absorption-type filtering power divider ii) according to the present invention, and a composite T-shaped network is adopted to replace a common isolation resistor, so that the dual functions of isolation and absorption are provided, thereby solving the problem of large size. Wherein the content of the first and second substances,Z S representing the value of the input port impedance,Z L representing the output port impedance value. Fig. 2-1 and fig. 2-2 are respectively a schematic structural diagram of a half-cut even-mode equivalent circuit and a half-cut odd-mode equivalent circuit of the present design.
To verify the dual characteristics of the composite T-network, the filter power divider is first analyzed, and an absorption branch (shown in fig. 3) is proposed to remove the input port loading (i.e., (ii) (iii))R a ；Z a ，θ a ) And common isolation resistor(s) is (are) between the input coupling feed linesR) An improved filtering power divider. Wherein the bandpass response is provided by a three-wire coupled structure. FIG. 4 is a schematic diagram of a three-wire coupling structure, in which the frequency response of the circuit based on the three-wire coupling structure can be obtained from the impedance matrix of its six portsV i AndI i (i=1,2,3,4,5,6) voltage and current applied to each port, respectively,Z oe 、Z oo is a function of the mode impedance,k cc is the ratio of the coupling coefficient between the non-adjacent two lines and the adjacent two lines. By substituting the respective endsWith two ports obtained by mouth conditionsSAnd (4) parameters.
For a detailed analysis, the original filtering power divider based on the three-wire coupling structure is analyzed, and fig. 5-1 and 5-2 specifically show the odd-even mode equivalent circuit of the original filtering power divider. As shown in FIG. 5-1, under the excitation of even mode, the 2, 4 and 6 ports are open, the 5 port is short, the 1 and 3 ports are respectively the output end and the input end, the port conditions are substituted into the impedance matrix of the six ports to simplify and obtain the two-port deviceZA matrix by which can be obtainedZ 11 、Z 12 、Z 21 、Z 22 . This gives rise to excitation in the even modeSAnd (4) parameters. As shown in FIG. 5-2, under excitation of odd mode, 2, 6 ports are open, 3, 5 ports are short, 4 ports are voltage, and can be regarded as a port circuit, and the input impedance at S2 port can be calculatedZoinFinding the excitation in the odd modeSAnd (4) parameters. And finally, combining the results of the odd-even mode analysis calculation to obtain the S parameter of the whole circuit. The frequency response curve of the original filtered power divider as shown in fig. 6 can thus be obtained. It can be seen that there are 3 Transmission Poles (TPs) and two Transmission Zeros (TZs) near the passband, by which the order problem can be well explained. The transmission poles in 3 bands can easily meet the design requirement of the broadband. And as can be seen from fig. 7, the bandwidth can be flexibly adjusted by changing the width of the three lines and the distance between the adjacent lines. In order to improve the selectivity of the passband, a short-circuit branch of quarter wavelength is loaded at the tail end of an output coupling feeder of the original filtering power divider (Z c ，θ c ) I.e. an improved filtering power divider as shown in fig. 3. FIG. 8 is a variation curve of transmission coefficient, which can be compared with the original filter power divider by adding a quarter-wavelength short-circuit branch (C)Z c ，θ c ) The bandwidth and the transmission zero points of two near pass bands can be flexibly adjusted, and higher selectivity is shown.
The above analysis summarizes: the improved filtering power divider can provide a broadband filtering response and has bandwidth and transmission zeroControllability of the dots. However, the reflected energy is reflected back to the input end, causing interference. Therefore, an absorption-type filtering power divider i shown in fig. 9 is proposed, which is based on an improved filtering power divider and replaces an isolation resistor R with the proposed composite T-shaped network. The transmission coefficient (#) of the absorption type filtering power divider I can be obtained through the same calculation derivation stepS 21 |) and input-end reflection coefficient (& ltS 11 |) and isolation coefficient (| calculation of the luminance)S 23 |) and output end reflection coefficient (& lt & gtluminance & gtS 22 |) whose frequency response curves are shown in fig. 10-1 and 10-2, respectively. Compared with the improved filter power divider, the absorption filter power divider I with the composite T-shaped structure can not only meet the isolation level between output ports, but also absorb out-of-band interference signals reflected back to the input port. It is well known that the performance of no reflection needs to consider both the in-band matching performance and the out-of-band matching performance. Therefore, for better non-reflective performance of the circuit for visual analysis, the in-band maximum reflection coefficient is definedRP max And out-of-band maximum reflection coefficientRS max 。RP max AndRS max the smaller the value of (b) represents the better the input non-reflective performance. FIG. 11-1 shows an absorption filter power divider I with a multiplexing T-shaped structureR b Lower partRP max AndRS max the change curve of (2). It will be readily seen that,R b change pair ofRS max Is very sensitive and is described inR b = 150 Ω, the minimum value is achieved, i.e. the out-of-band matching/absorption performance is the best. FIG. 11-2 shows different absorption type filtering power dividers I with multiplexing T-shaped structuresR b The matching performance and the isolation level of the lower output port. Wherein for an intuitive analysis an offset frequency Δ is definedf= 0.6GHz at the center frequency by analysisf 0 Is at and aroundf 0 ±ΔfOutput end reflection coefficient ofS 22 And at the center frequencyf 0 Is treated withf 0 – Δf，f 0 + Δf]Maximum isolation coefficient between output ports in frequency rangeS 23 | max The influence of parameter change on the matching performance and isolation level of the output port can be visually analyzed, and the calculation can be carried outS 22 L and LS 23 | max The smaller the size, the better. Final comprehensive considerationR b At 150 Ω, the absorption filter power divider i can obtain a good compromise between input non-reflection performance, matching performance of the output ports, and isolation performance between the output ports. FIG. 12 shows different absorption type filtering power dividers I with multiplexing T-shaped structuresZ b Lower partRP max AndRS max can see the change curve ofZ b A reasonable value of (a) can result in a good compromise of in-band matching performance and out-of-band matching performance.
By the aid of the absorption type filtering power divider I with the composite T-shaped structure, a certain absorption effect is achieved by multiplexing the T-shaped network under the condition that a certain isolation level is guaranteed. Therefore, in order to further improve the absorption performance of the reflected signal at the input end, only a section of absorption branch is needed to be loaded at the input end, and a structural schematic diagram of the final circuit of the invention is provided, namely an absorption type filtering power divider II shown in fig. 1. Due to its symmetrical circuit structure, the method of odd-even mode analysis can also be used. Fig. 2-1 and 2-2 are schematic structural diagrams of half-cut-even mode and odd mode equivalent circuits of a compact absorption filter power divider according to the present invention, respectively. The specific calculation method is to substitute the port condition into the six-port impedance matrix and deduce the circuit by calculationSParameters, when analyzing even-mode equivalent circuits, the source impedances in equations (4) - (6) and (8) - (11) are usedZ s By replacement withZ s’ = Z s //Z in1 In whichZ in1 = R a + jZ a tanθ a . FIG. 13-1 shows transmission coefficients (& gtY & ltT & gt) of the absorption type filter power divider I according to the present inventionS 21 | and input-end reflection coefficient (& lt & gt)S 11 | comparison plotFIG. 13-2 shows the isolation coefficient (& gtT & lt) of the present invention from the absorption type filter power divider IS 23 |) and output end reflection coefficient (& lt & gtluminance & gtS 22 | from the table). It can be seen that the absorption branch added at the input port of the present invention significantly improves the out-of-band absorption level, which is achieved by an absorption resistor (A)R a ) And a short-circuit branch of quarter wavelength (Z a ，θ a ) And (4) forming. FIGS. 14-1 and 14-2 are different views of the present inventionZ a AndR a lower transmission coefficient ([ mu ] L)S 21 | and input-end reflection coefficient (& lt & gt)S 11 |) change curve. FIG. 15 shows a variation of the present inventionR a Lower partRP max AndRS max the change curve of (2). Can be obtained by analysis, withZ a Reduced, improved absorption energy absorption, but at the same timeZ a Smaller also means wider line widths. At the same time, by changingR a Can be further adjusted on the premise of not influencing the filtering performanceRP max AndRS max by changingR a The input non-reflection performance of the invention can be independently regulated and controlled. When in useR a = 50 Ω hourRS max I.e. when the absorption performance for out-of-band reflected signals is optimal. Therefore, the temperature of the molten metal is controlled,R a set to 50 Ω.
Based on the analysis, a compact absorption type filtering power divider with the structure shown in fig. 1 is designed. Fig. 16 is a top perspective view of a compact absorption filter power divider according to the present embodiment, with specific parameters given. FIGS. 17-1 and 17-2 are graphs respectively showing transmission coefficients (& gtnon & gt) of a compact absorption filter power divider according to this exampleS 21 |), input end reflection coefficient (#)S 11 | and isolation coefficient (& lt & gt)S 23 |), reflection coefficient of output end (#)S 22 |) the simulation results and the test results show good consistency. The center frequency of the FBW is 2.36GHz and 1-dB FBW is measured by final test52.8%, a minimum in-band insertion loss of 0.32dB, four out-of-band zeros as calculated to be consistent, an impedance rejection level of greater than 27dB, an isolation level of greater than 16dB, and good absorption performance (#) throughout the frequency range testedS 11 |<10 dB) and a final circuit size of 0.31λ g ×0.15λ g (λ g A waveguide wavelength at a center frequency of 2.36 GHz). In general, the design of a miniaturized broadband absorption type filter power divider with good absorption performance, good isolation level and good passband performance is realized.
The embodiments of the present invention have been described above with reference to the drawings, and the present invention may have other embodiments in addition to the above embodiments. All technical solutions formed by adopting equivalent substitutions or equivalent transformations fall within the protection scope of the claims of the present invention.
Claims (9)
1. The utility model provides a compact absorption type filtering power divider, includes the filtering power divider and loads in the absorption minor matters, an input port (S1) and two output ports (S2, S3) of filtering power divider input, its characterized in that: the filtering power divider comprises two band-pass filters with three-wire coupling structures and a composite T-shaped network arranged between the input ends of the two band-pass filters, wherein the composite T-shaped network comprises two symmetrical isolation resistors (8 and 8 ') arranged between the input ends of the two band-pass filters and a first quarter-wavelength short-circuit branch (9) loaded between the two isolation resistors (8 and 8').
2. The compact absorptive filter power divider of claim 1, wherein: and the output side of the band-pass filter of the three-wire coupling structure is loaded with second quarter-wavelength short-circuit branches (7, 7').
3. The compact absorptive filter power divider of claim 2, wherein: the band-pass filter of the three-wire coupling structure includes: quarter-wavelength input coupling feeders (4, 4 ') and quarter-wavelength output coupling feeders (5, 5 ') are arranged on the left and right sides of the quarter-wavelength central short-circuit branches (6, 6 ') in parallel and symmetrically, first ends of the quarter-wavelength input coupling feeders (4, 4 ') of the two band-pass filters are connected with the input port (S1), and second ends of the quarter-wavelength input coupling feeders (4, 4 ') of the two band-pass filters are connected with the composite T-shaped network; the first ends of the quarter-wavelength output coupling feeders (5, 5 ') of the two band-pass filters are respectively connected with the two output ports (S2, S3), and the second ends of the quarter-wavelength output coupling feeders (5, 5 ') of the two band-pass filters are respectively loaded with the second quarter-wavelength short-circuit branches (7, 7 ').
4. The compact absorptive filter power divider of claim 1, wherein: the absorption branch is a third quarter-wavelength short-circuit branch (11) loaded on the input port (S1) through an absorption resistor (10).
5. The compact absorptive filter power divider of claim 3, wherein: the input port (S1) is connected with the quarter-wavelength input coupling feeders (4, 4 ') of the two band-pass filters sequentially through the transmission line input line (1) and the input end impedance matching line (2), and the output ports (S2, S3) are connected with the quarter-wavelength output coupling feeders (5, 5 ') through the output end transmission lines (3, 3 ') respectively.
6. The compact absorptive filter power divider of claim 5, wherein: the input transmission line (1) and the output transmission lines (3, 3') are both 50 omega transmission lines.
7. The compact absorptive filter power divider of claim 1, wherein: the first quarter-wavelength short-circuit branch knot (9) is short-circuited and grounded through a first metalized through hole (15); the second quarter-wave short-circuit branches (7, 7 ') are short-circuited and grounded through second metalized through holes (13, 13'); the third quarter-wave short-circuit branch (11) is short-circuited and grounded through a third metalized through hole (14).
8. The compact absorptive filter power divider of claim 1, wherein: the filter power divider is characterized by comprising an upper metal strip layer, a middle medium substrate and a lower metal ground layer, wherein the filter power divider and an absorption branch loaded at the input end of the filter power divider are arranged on the upper metal strip layer.
9. The compact absorption-type filter power divider according to claim 1, wherein: the composite T-shaped network is multiplexed into an absorption branch while meeting the isolation level, and has the dual characteristics of isolation and absorption.
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