Broadband SIW Antenna Matching Method

Abstract

This invention discloses a broadband SIW antenna matching method, belonging to the field of antenna technology. This method cascades a broadband impedance matching layer consisting of several matching stubs and a waveguide transmission line behind the SIW antenna. The reflection coefficients of the ports following the cascaded matching stubs and waveguide transmission line are calculated based on cascaded two-port network theory. Finally, a genetic algorithm is used to optimize the impedance matching within the target frequency band. This method performs broadband impedance matching optimization in just a few minutes, improving optimization efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of antennas, and in particular relates to a broadband SIW antenna matching method. Background Art

[0002] Antennas are at the front end (receiver) or the end end (transmitter) of all communication systems, and are used to transmit and receive signals. Therefore, the performance of the antenna directly affects the performance of the entire communication system. Improving antenna performance will improve the performance of the entire communication system. For antennas, bandwidth is a very important performance indicator. Broadband antennas can achieve a wider communication frequency band. Broadband communication means increased communication capacity and can provide users with more operating frequency bands to choose from. Different frequency bands implement different functions. Currently, different application scenarios have different communication protocols corresponding to different communication frequency bands. For example, wireless LAN, 5G communication, 4G communication, Bluetooth, navigation communication, etc. operate in different frequency bands. If the antenna operates in a very wide frequency band, it can not only cover multiple communication scenarios at the same time but also save costs.

[0003] Broadband matching is to change the antenna's radiation impedance Z ant The impedance of the matching network is transformed to match the impedance of the feed port, allowing the antenna to operate over a wider frequency band. Most broadband matching work actually revolves around matching layer design. Broadband matching layers generally require multiple stages of matching to achieve a wider bandwidth. By designing the matching layer to achieve a better impedance after transformation, the antenna impedance within the broadband is matched to the port impedance after transformation through the matching layer. From a circuit perspective, all broadband impedance matching layers can be equivalent to a matching circuit consisting of inductors, capacitors, and resistors. Unlike RF broadband matching circuits, the value of each component in the antenna matching layer equivalent circuit is frequency-dependent.

[0004] Broadband matching for antennas is primarily achieved through broadband matching layers. Existing broadband matching layer optimization designs typically rely on parameter scanning or optimization using full-wave simulation software. After determining the matching layer structure and key parameters, these parameters are scanned or optimized using full-wave simulation software until a satisfactory result is achieved. For complex models with numerous critical dimensions, optimization can often take dozens of hours, resulting in a time-consuming and inefficient approach. Summary of the Invention

[0005] The purpose of the present invention is to achieve broadband impedance matching of SIW antennas, reduce optimization time and improve optimization efficiency, and provide a broadband SIW antenna matching method.

[0006] The technical problem proposed by the present invention is solved as follows:

[0007] A broadband SIW antenna matching method comprises the following steps:

[0008] Step 1. Configure the broadband impedance matching layer of the SIW antenna

[0009] The SIW antenna is a hollow substrate integrated waveguide with no dielectric filling. Lateral slots are cut on the metal wall of the upper surface for radiation. A broadband impedance matching layer is cascaded behind the SIW antenna. The broadband impedance matching layer includes N / 2 units cascaded in sequence. Each unit includes a waveguide transmission line and a matching branch cascaded in sequence, where N / 2 is a positive integer. The waveguide transmission line is a waveguide with the same thickness and width as the SIW antenna. The matching branch includes a waveguide segment and two metal branches. The waveguide segment is a waveguide with the same thickness and width as the SIW antenna. The two metal branches are located inside the waveguide segment, symmetrical about the center of the waveguide segment, and tightly fit the sidewalls of the waveguide segment.

[0010] Step 2. Divide the operating frequency band into 1001 equally spaced frequency points and use electromagnetic simulation software to obtain the port reflection coefficient Γ of the SIW antenna at 1001 equally spaced frequency points. ant ;

[0011] The metal branch length i is used as a scanning parameter variable with a scanning range of 0-10 mm and a scanning step of 0.05. The S parameters of the matching branch corresponding to each metal branch length i are scanned and simulated to obtain a matching branch S parameter data set, namely the S parameters of the matching branch corresponding to 201 equally spaced metal branch lengths and 1001 equally spaced frequency points.

[0012] Step 3. Use a genetic algorithm to optimize the S parameters of the cascaded SIW antenna with a broadband impedance matching layer at 1001 equally spaced frequency points. The optimization variables in the genetic algorithm are set to the metal branch length i and the length of the waveguide transmission line.

[0013] The objective function Obj in the genetic algorithm is set as:

[0014]

[0015] in,

[0016]

[0017] in, It represents the port reflection coefficient of the SIW antenna with a cascaded broadband impedance matching layer at the mth equally spaced frequency point, 1≤m≤1001;

[0018] The cutoff condition in the genetic algorithm is set as: objective function Obj=0.

[0019] Furthermore, in step 1, the length of the waveguide section in the matching branch is λ / 5.

[0020] Furthermore, in step 1, the thickness a of the hollow substrate integrated waveguide is 3 mm, and the width b is 25.16 mm; the slot length c is 18.88 mm, the slot width e is 2.52 mm, the distance d between the long side of the slot and the short-circuit end of the waveguide is 6.32 mm, and the distance f between the long side of the slot and the waveguide port is 2 mm; the thickness a of the metal branch node is 3 mm, the width g is 2 mm, and the spacing h between the two sides and the edge of the matching branch node is 2 mm.

[0021] Furthermore, in step 3, the port reflection coefficient of the SIW antenna cascaded with a broadband impedance matching layer is The solution process is:

[0022]

[0023]

[0024] …

[0025]

[0026]

[0027] in, It represents the port reflection coefficient of the SIW antenna with n two-port networks cascaded at the mth equally spaced frequency point, 1≤n≤N; and The S11, S12, S21 and S22 values ​​of the nth two-port network are represented respectively; when n is an odd number, the nth two-port network is the waveguide transmission line in the (n+1) / 2th unit in the broadband impedance matching layer; when n is an even number, the nth two-port network is the matching branch in the n / 2th unit in the broadband impedance matching layer.

[0028] Furthermore, in step 3, the S parameter solution process of the waveguide transmission line is:

[0029] Calculate the S parameters of the two-port network based on the length of the waveguide transmission line in the current iteration:

[0030]

[0031]

[0032]

[0033]

[0034] Where A, B, C, and D represent the ABCD matrices corresponding to the waveguide transmission line in the current iteration:

[0035] A=cos(βl)

[0036] B=jZ0 sin(βl)

[0037] C=jY0 cos(βl)

[0038] D=cos(βl)

[0039] Where l represents the length of the waveguide transmission line in the current iteration, β represents the transmission constant, represents characteristic impedance, k represents wave number, η represents characteristic wave impedance, and Y0 represents characteristic admittance.

[0040] Furthermore, in step 3, the S parameter solution process of the matching branch is:

[0041] The S parameters of the matching branch obtained by simulating the metal branch length i and the scanning parameters are used to calculate the S parameters of the matching branch in the current iteration. If the metal branch length i value in the current iteration belongs to the matching branch S parameter data set, the S parameters of the matching branch corresponding to the metal branch length i value in the matching branch S parameter data set are directly called. Otherwise, the S parameters of the matching branch are calculated:

[0042] The two metal branch length values ​​closest to the metal branch length i value in the current iteration in the scan parameter dataset are recorded as L1 and L2 respectively, and L2>L1. The S parameter of the matching branch corresponding to the metal branch length i value in the current iteration is:

[0043]

[0044]

[0045]

[0046]

[0047] Among them, S 11 (i) S 12 (i) S 21 (i) and S 22 (i) represents the S11, S12, S21 and S22 values ​​of the matching branch corresponding to the metal branch length i value in the current iteration number; S 11 (L1), S 12 (L1), S 21 (L1) and S 22 (L1) represents the S11, S12, S21 and S22 values ​​of the matching branch corresponding to the metal branch length L1; S 11 (L2), S 12 (L2), S 21 (L2) and S 22(L2) represents the S11, S12, S21 and S22 values ​​of the matching branch corresponding to the metal branch length L1;

[0048] The beneficial effects of the present invention are:

[0049] The method described in this paper cascades a broadband impedance matching layer consisting of several matching stubs and a waveguide transmission line behind the SIW antenna. The reflection coefficients of the ports following the cascaded matching stubs and waveguide transmission line are calculated based on cascaded two-port network theory. Finally, a genetic algorithm is used to optimize the impedance matching across the target frequency band. This method performs broadband impedance matching optimization in just a few minutes, improving optimization efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 Schematic diagram of the structure of the SIW antenna in the method of the present invention;

[0051] Figure 2 Schematic diagram of the structure of the matching branch in the method of the present invention;

[0052] Figure 3 Schematic diagram of an equivalent network of a SIW antenna cascaded with a broadband impedance matching layer in the method of the present invention;

[0053] Figure 4 A schematic diagram of the structure and dimensions of a SIW antenna cascaded with a broadband impedance matching layer in the method described in the embodiment;

[0054] Figure 5 This is a comparison chart of the port reflection coefficient obtained by optimization in the embodiment and the port reflection coefficient obtained by actual CST simulation;

[0055] Figure 6 Schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0056] The present invention will be further described below with reference to the accompanying drawings and examples.

[0057] This embodiment provides a broadband SIW antenna matching method. Several broadband impedance matching layers are cascaded behind the SIW antenna. The broadband impedance matching layers include matching stubs and waveguide transmission lines. The port reflection coefficients after the cascaded matching stubs and waveguide transmission lines are calculated based on the cascaded two-port network theory, and the impedance matching of the frequency band is optimized using a genetic algorithm.

[0058] The method described in this embodiment specifically includes the following steps:

[0059] Step 1. Configure the broadband impedance matching layer of the SIW antenna

[0060] The structural diagram of SIW antenna is as follows Figure 1As shown in FIG, it is a hollow substrate integrated waveguide with no dielectric filling and a transverse slot on the metal wall on the upper surface for radiation. A broadband impedance matching layer is cascaded behind the SIW antenna. The broadband impedance matching layer includes a number of units cascaded in sequence. Each unit includes a waveguide transmission line and a matching branch cascaded in sequence. The waveguide transmission line is a waveguide with the same thickness and width as the SIW antenna. The structural diagram of the matching branch is shown in FIG. Figure 2 As shown, it includes a waveguide section and two metal branches. The waveguide section is a waveguide with the same thickness and width as the SIW antenna and a length of λ / 5. The two metal branches are located inside the waveguide section, symmetrical about the center of the waveguide section, and tightly fit with the side wall of the waveguide section.

[0061] In this embodiment, the thickness a of the waveguide is 3 mm, and the width b is 25.16 mm; the slot length c is 18.88 mm, the slot width e is 2.52 mm, the distance d between the long side of the slot and the short-circuit end of the waveguide is 6.32 mm, and the distance f between the long side of the slot and the waveguide port is 2 mm; the thickness a of the metal branch is 3 mm, the width g is 2 mm, the length i is variable, and the spacing h between the two sides and the edge of the matching branch is 2 mm.

[0062] Step 2. In the commercial electromagnetic simulation software CST, the operating frequency band is divided into 1001 equally spaced frequency points, and the port reflection coefficient Γ of the SIW antenna at 1001 equally spaced frequency points is simulated. ant ;

[0063] In order to subsequently fit the S parameters of the matching branch of unknown length, it is necessary to scan the parameters to collect the matching branch S parameter data set. The metal branch length i is used as the scanning parameter variable, the scanning range is 0-10mm, and the scanning step is 0.05. The S parameters of the matching branch corresponding to 201 equally spaced metal branch lengths and 1001 equally spaced frequency points are obtained.

[0064] Step 3. Use a genetic algorithm to optimize the S parameters of the cascaded SIW antenna with a broadband impedance matching layer at 1001 equally spaced frequency points. The optimization variables in the genetic algorithm are set to the metal branch length i and the length of the waveguide transmission line.

[0065] The setting process of the objective function in the genetic algorithm is:

[0066] Port reflection coefficient Γ of a cascaded two-port network in for:

[0067]

[0068] in, and are the S11, S12, S21, and S22 values ​​of the two-port network, Γ is the port reflection coefficient of one-port network of the cascaded two-port network;

[0069] In this embodiment, the broadband impedance matching layer includes three units cascaded in sequence, that is, the two-port network cascaded after the SIW antenna includes three sections of waveguide transmission lines and three matching branches;

[0070] The equivalent network diagram of the SIW antenna cascaded with a broadband impedance matching layer is shown in the figure below. Figure 3 As shown, six two-port networks are cascaded after the SIW antenna;

[0071] The port reflection coefficient Γ6 of the SIW antenna cascaded with a broadband impedance matching layer is calculated according to the port reflection coefficient solution formula of the cascaded two-port network:

[0072]

[0073] …

[0074]

[0075]

[0076] The objective function in the genetic algorithm is:

[0077]

[0078]

[0079] in, is the Γ6 value of the mth equally spaced frequency point;

[0080] For a waveguide transmission line, the S parameters of the two-port network are calculated based on the length of the waveguide transmission line in the current iteration:

[0081]

[0082]

[0083]

[0084]

[0085] Where A, B, C, and D represent the ABCD matrices corresponding to the waveguide transmission line in the current iteration:

[0086] A=cos(βl)

[0087] B=jZ0 sin(βl)

[0088] C=jY0 cos(βl)

[0089] D=cos(βl)

[0090] Where l represents the length of the waveguide transmission line in the current iteration, β represents the transmission constant, represents characteristic impedance, k represents wave number, η represents characteristic wave impedance, and Y0 represents characteristic admittance.

[0091] For the matching branch, the S parameters of the matching branch obtained by the metal branch length i and the scan parameter are used to calculate the S parameters of the matching branch in the current iteration. If the metal branch length i value in the current iteration belongs to the scan parameter dataset, the S parameters of the matching branch corresponding to the metal branch length i value in the scan parameter dataset are directly called. Otherwise, the S parameters of the matching branch are calculated by interpolation fitting.

[0092] The specific process of calculating the S parameters of the matching branch using interpolation fitting is as follows:

[0093] The two metal branch length values ​​closest to the metal branch length i value in the current iteration in the scan parameter dataset are recorded as L1 and L2 respectively, and L2>L1. The S parameter of the matching branch corresponding to the metal branch length i value in the current iteration is:

[0094]

[0095]

[0096]

[0097]

[0098] The cutoff condition in the genetic algorithm is set as: objective function Obj=0.

[0099] In this embodiment, when calculating the objective function in each iteration, the genetic algorithm first gives the values ​​of six optimization variables, and then Figure 3 The model calculates the port reflection coefficient Γ6 of a SIW antenna cascaded with a broadband impedance matching layer. If the port reflection coefficient at a certain frequency point is less than 0.3, the objective function value corresponding to that frequency point after the decision is set to 0. If the port reflection coefficient at that frequency point is greater than 0.3, the objective function value after the decision is the difference between the port reflection coefficient before the decision and 0.3. The final objective function value is the sum of the objective function values ​​after the decision of the port reflection coefficients at all frequencies. The genetic algorithm optimizes the objective function by changing the variable values ​​according to the iterative results. Optimization is complete when the objective function reaches 0.

[0100] The antenna operating frequency band of this embodiment is 7.7-10.5 GHz, and the optimized SIW antenna model is as follows: Figure 4As shown, the length of the first matching branch i1 is 5.22 mm, the length of the second matching branch i2 is 4.46 mm, the length of the third matching branch i3 is 3.09 mm, the length l1 of the first waveguide transmission line is 3.05 mm, the length l2 of the second waveguide transmission line is 10.85 mm, and the length l3 of the third waveguide transmission line is 9.34 mm.

[0101] The comparison between the optimized port reflection coefficient and the actual CST calculated port reflection coefficient is shown in the figure below. Figure 5 As shown, s11_ant represents the port reflection coefficient of the SIW slot antenna before broadband impedance matching, s11_3stub_opt represents the port reflection coefficient obtained by genetic algorithm optimization, and s11_3stub_cst represents the port reflection coefficient obtained by CST modeling of the optimized size. Figure 5 It can be seen that the bandwidth expansion effect is obvious and the optimization results are highly consistent with the CST calculation results.

[0102] The schematic flow diagram of the method of the present invention is as follows Figure 6 As shown in the figure, this optimization was performed on a desktop computer with an Intel(R) Core(TM) i5-10400(R) CPU, a CPU frequency of 2.9GHz, and 32GB of memory. The optimization took 515 seconds, which greatly reduced the optimization time and improved the optimization efficiency.

Claims

1. A broadband SIW antenna matching method, characterized in that: The following steps are involved: Step 1. Configure the broadband impedance matching layer of the SIW antenna The SIW antenna is a hollow substrate integrated waveguide with no dielectric filling. Lateral slots are cut on the metal wall of the upper surface for radiation. A broadband impedance matching layer is cascaded behind the SIW antenna. The broadband impedance matching layer includes N / 2 units cascaded in sequence. Each unit includes a waveguide transmission line and a matching branch cascaded in sequence, where N / 2 is a positive integer. The waveguide transmission line is a waveguide with the same thickness and width as the SIW antenna. The matching branch includes a waveguide segment and two metal branches. The waveguide segment is a waveguide with the same thickness and width as the SIW antenna. The two metal branches are located inside the waveguide segment, symmetrical about the center of the waveguide segment, and tightly fit the sidewalls of the waveguide segment. Step 2. Divide the operating frequency band into 1001 equally spaced frequency points and use electromagnetic simulation software to obtain the port reflection coefficient Γ of the SIW antenna at 1001 equally spaced frequency points. ant ; The metal branch length i is used as a scanning parameter variable with a scanning range of 0-10 mm and a scanning step of 0.

05. The S parameters of the matching branch corresponding to each metal branch length i are scanned and simulated to obtain a matching branch S parameter data set, namely the S parameters of the matching branch corresponding to 201 equally spaced metal branch lengths and 1001 equally spaced frequency points. Step 3. Use a genetic algorithm to optimize the S parameters of the cascaded SIW antenna with a broadband impedance matching layer at 1001 equally spaced frequency points. The optimization variables in the genetic algorithm are set to the metal branch length i and the length of the waveguide transmission line. The objective function Obj in the genetic algorithm is set as: in, in, It represents the port reflection coefficient of the SIW antenna with a cascaded broadband impedance matching layer at the mth equally spaced frequency point, 1≤m≤1001; The cutoff condition in the genetic algorithm is set as: objective function Obj=0.

2. The broadband SIW antenna matching method according to claim 1, wherein: In step 1, the length of the waveguide section in the matching branch is λ / 5.

3. The broadband SIW antenna matching method according to claim 1, wherein: In step 1, the thickness a of the hollow substrate integrated waveguide is 3 mm, and the width b is 25.16 mm; the slot length c is 18.88 mm, the slot width e is 2.52 mm, the distance d between the long side of the slot and the short-circuit end of the waveguide is 6.32 mm, and the distance f between the long side of the slot and the waveguide port is 2 mm; the thickness a of the metal branch node is 3 mm, the width g is 2 mm, and the spacing h between the two sides and the edge of the matching branch node is 2 mm.

4. The broadband SIW antenna matching method according to claim 1, wherein: In step 3, the port reflection coefficient of the SIW antenna cascaded with a broadband impedance matching layer is The solution process is: … in, It represents the port reflection coefficient of the SIW antenna with n two-port networks cascaded at the mth equally spaced frequency point, 1≤n≤N; and The S11, S12, S21 and S22 values ​​of the nth two-port network are represented respectively; when n is an odd number, the nth two-port network is the waveguide transmission line in the (n+1) / 2th unit in the broadband impedance matching layer; when n is an even number, the nth two-port network is the matching branch in the n / 2th unit in the broadband impedance matching layer.

5. The broadband SIW antenna matching method according to claim 4, characterized in that: In step 3, the S-parameter solution process of the waveguide transmission line is: Calculate the S parameters of the two-port network based on the length of the waveguide transmission line in the current iteration: Where A, B, C, and D represent the ABCD matrices corresponding to the waveguide transmission line in the current iteration: A=cos(βl) B=jZ0sin(βl) C=jY0cos(βl) D=cos(βl) Where l represents the length of the waveguide transmission line in the current iteration, β represents the transmission constant, represents characteristic impedance, k represents wave number, η represents characteristic wave impedance, and Y0 represents characteristic admittance.

6. The broadband SIW antenna matching method according to claim 4, characterized in that: The S-parameter solution process of the matching branch is: The S parameters of the matching branch obtained by simulating the metal branch length i and the scanning parameters are used to calculate the S parameters of the matching branch in the current iteration. If the metal branch length i value in the current iteration belongs to the matching branch S parameter data set, the S parameters of the matching branch corresponding to the metal branch length i value in the matching branch S parameter data set are directly called. Otherwise, the S parameters of the matching branch are calculated: The two metal branch length values ​​closest to the metal branch length i value in the current iteration in the scan parameter dataset are recorded as L1 and L2 respectively, and L2>L1. The S parameter of the matching branch corresponding to the metal branch length i value in the current iteration is: Among them, S 11 (i) S 12 (i) S 21 (i) and S 22 (i) represents the S11, S12, S21 and S22 values ​​of the matching branch corresponding to the metal branch length i value in the current iteration number; S 11 (L1), S 12 (L1), S 21 (L1) and S 22 (L1) represents the S11, S12, S21 and S22 values ​​of the matching branch corresponding to the metal branch length L1; S 11 (L2), S 12 (L2), S 21 (L2) and S 22 (L2) represents the S11, S12, S21 and S22 values ​​of the matching branch corresponding to the metal branch length L1.

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