A ring bandstop filter with quasi-elliptic function response and a design method thereof

Abstract

The application discloses a ring-shaped band-stop filter with quasi-elliptic function response and a design method thereof. The ring-shaped band-stop filter comprises two source-end impedance units, a first branch connected between the two source-end impedance units, the first branch comprising a first transmission line and two second transmission lines, and the first transmission line being connected between the two second transmission lines, and a second branch in parallel with the first branch, the second branch comprising a third transmission line and two coupling lines, and the third transmission line being connected between the two coupling lines. The ring-shaped band-stop filter with quasi-elliptic function response provided by the application can generate more transmission zero points and reflection zero points, so that the device has a wider stop band bandwidth and higher frequency selectivity; and the ring-shaped structure of the circuit reduces the circuit size, has the smallest circuit area compared with other band-stop filters, and realizes the miniaturized design of the circuit.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of band-stop filter, in particular to a ring-shaped band-stop filter with quasi-elliptic function response and a design method thereof. BACKGROUND

[0002] The current research of band-stop filter is mainly divided into three types of planar circuit, multilayer board circuit and waveguide structure circuit, among which the design of planar circuit is the easiest. There are quasi-elliptic band-stop filter circuits based on planar circuit design, but their circuit size is large, the bandwidth is narrow and they do not have good frequency selectivity. In order to obtain wideband ripple response, Chebyshev response is most widely used. But this method cannot produce more out-of-band zeros, resulting in very limited frequency selectivity of the device.

[0003] Most of the current band-stop filters do not have enough transmission zeros and reflection zeros, resulting in insufficient bandwidth and poor frequency selectivity, and the structure of most circuits is not compact, the circuit size is large, which is not conducive to application in communication systems. SUMMARY

[0004] One of the purposes of the present application is to provide a ring-shaped band-stop filter with quasi-elliptic function response, which can increase the number of transmission zeros and reflection zeros, has the performance of wide stop band and high frequency selectivity.

[0005] The second purpose of the present application is to provide a design method of a ring-shaped band-stop filter with quasi-elliptic function response, which determines the impedance values of the transmission line and the coupling line according to the constraint conditions, so as to ensure that the designed band-stop filter meets the required performance requirements.

[0006] The technical scheme provided by the present application is as follows:

[0007] A ring-shaped band-stop filter with quasi-elliptic function response comprises:

[0008] Two source-end impedance units;

[0009] A first branch connected between the two source-end impedance units;

[0010] The first branch comprises a first transmission line and two second transmission lines, and the first transmission line is connected between the two second transmission lines.

[0011] A second branch in parallel with the first branch;

[0012] The second branch comprises a third transmission line and two coupling lines, and the third transmission line is connected between the two coupling lines.

[0013] Preferably, the two coupling lines are forward coupling lines or reverse coupling lines.

[0014] Preferably, the first transmission line, the second transmission line, the third transmission line and the coupling line each have an electrical length of 90° at a center frequency.

[0015] A design method of a ring band-stop filter with quasi-elliptic function response, for designing the ring band-stop filter with quasi-elliptic function response, comprising the following steps:

[0016] Step one, determining the overall transmission matrix of the band-stop filter circuit;

[0017] Step two, obtaining the input reflection coefficient S 11 and the forward transmission coefficient S 21 of the band-stop filter circuit according to the overall transmission matrix;

[0018] Step three, taking the ripple height of S 11 and S 21 as constraint conditions, determining the impedance values of the first transmission line, the second transmission line, the third transmission line and the coupling line corresponding to the constraint conditions.

[0019] Preferably, in the step one, the overall transmission matrix is

[0020] Wherein, A tot =(A up B down +A down B up ) / (B up +B down )=D tot ;

[0021] B tot =B up B down / (B up +B down );

[0022] C tot =(C up +C down )+(A up -A down )(D down -D up ) / (B up +B down );

[0023] Wherein, A up , B up , C up and Dup These are elements in the transmission matrix of the first branch, A. down B down C down and D down These are the elements in the transmission matrix of the second branch.

[0024] Preferably, in step two, the incident reflection coefficient S is obtained through the following relationship. 11 and forward transmission coefficient S 21 :

[0025] S 11 = (B tot -C tot ) / (A tot +B tot +C tot +D tot )

[0026] S 21 =2 / (A) tot +B tot +C tot +D tot )

[0027] F circuit =S 11 / S 21 = (B tot -C tot ) / 2;

[0028] Among them, F circuit For S 11 With S 21 The ratio function.

[0029] Preferably, when the two coupling lines are positive coupling lines:

[0030]

[0031] in, S indicates that the two coupled lines are positively coupled. 11 With S 21 The ratio of p; n (n = 0, 1, 2, 3, 4, 5, 7) represents the corresponding sin n The coefficient of θ.

[0032] Preferably, when the two coupling lines are reverse coupling lines:

[0033]

[0034] in, S indicates that the two coupled lines are in opposite directions. 11S 21 g n (n = 0, 1, 2, 3, 4, 5, 7) is the coefficient of the corresponding sin n θ.

[0035] The beneficial effects of the present application are:

[0036] The ring-shaped band-stop filter with quasi-elliptic function response provided by the present application has quasi-elliptic function capable of generating more transmission zeros and reflection zeros, so that the device has a wider stopband bandwidth and higher frequency selectivity; and the ring-shaped structure of the circuit reduces the circuit size, and compared with other band-stop filters, has the smallest circuit area, realizing the miniaturization design of the circuit.

[0037] The design method of the ring-shaped band-stop filter with quasi-elliptic function response provided by the present application determines the impedance values of the transmission line and the coupling line according to the constraint conditions, which can ensure that the designed band-stop filter meets the required performance requirements. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 The ring-shaped band-stop filter circuit topology of the forward coupling line described in the present application.

[0039] Figure 2 The ring-shaped band-stop filter circuit topology of the reverse coupling line described in the present application.

[0040] Figure 3 The S parameter graph of the forward coupling structure in the embodiment of the present application.

[0041] Figure 4 The S parameter graph of the reverse coupling structure in the embodiment of the present application.

[0042] Figure 5 The layout graph of the circuit topology structure in the test example of the present application.

[0043] Figure 6 The simulation and test graph of the circuit S parameter in the test example of the present application. DETAILED DESCRIPTION

[0044] The present application will be further described in detail below with reference to the accompanying drawings, so that those skilled in the art can implement it according to the description.

[0045] The professional terms involved in the present application are explained as follows:

[0046] Band-stop filter: refers to a filter that can pass most frequency components, but attenuates certain range of frequency components to a very low level, which is opposite to the concept of band-pass filter.

[0047] Frequency selectivity refers to the rate at which a signal decays at the boundary between the passband and the stopband. A rapid decay indicates a clear boundary between the passband and stopband, signifying high frequency selectivity.

[0048] Elliptic functions: In the field of microwave devices, elliptic functions refer to functions that enable the S-axis of a device to... 11 and S 21 Simultaneously exhibiting a function with equal ripple response, and S 11 and S 21 The number of zeros is equal.

[0049] Quasi-elliptic functions: Similar to elliptic functions, but S 11 and S 21 The number of zeros is not equal.

[0050] Equal ripple response: refers to the ripple-like characteristics exhibited by the amplitude response of a filter in the passband and stopband. The presence of ripple-like characteristics can enable the filter to have good penetration and suppression within a certain frequency band, which is of great significance in industrial production.

[0051] This invention provides a ring bandstop filter with a quasi-elliptic function response and its design method. For example... Figures 1-2 As shown, depending on the coupling method of the coupled lines, the ring bandstop filter includes two circuit structures. Z0 is the source impedance unit. The circuit is divided into upper and lower paths. The upper path (first branch) consists of three microstrip transmission lines, and the lower path (second branch) consists of two coupled lines and one transmission line. Z1, Z2, and Z3 represent the characteristic impedances of the first, second, and third transmission lines, respectively. ev Z od The characteristic impedance of the coupled line is represented by θ, and the electrical lengths of the transmission line and the coupled line are 90° at the center frequency. Figure 1 This is the circuit topology diagram for a forward-coupled line. Figure 2 This is a circuit topology diagram of a reverse-coupled line.

[0052] The ABCD matrices of the forward and reverse coupling lines are as follows:

[0053]

[0054]

[0055] Where S = Z ev +Z od T = Z ev -Z od (1c)

[0056] In the formula, The matrix of forward coupling lines is ABCD. ABCD matrix of the backward-coupled line; j represents an imaginary number.

[0057] ABCD matrix of the transmission line is where i = 1, 2, 3;

[0058]

[0059] Figure 1 ABCD matrix (transmission matrix) of the circuit structure in the upper path (first branch) and the lower path (second branch) is respectively:

[0060]

[0061]

[0062] ABCD matrix of the overall circuit structure is:

[0063] A tot = (A up B down + A down B up ) / (B up +B down ) = D tot (4a)

[0064] B tot = B up B down / (B up +B down ) (4b)

[0065] C tot = (C up +C down )+(A up -A down )(D down -D up ) / (B up +B down ) (4c)

[0066] Finally, S 11 and S 21 of the band-stop filter can be expressed as

[0067] S 11 = (B tot -C tot ) / (A tot +B tot +C tot +D tot ) (5a)

[0068] S 21 = 2 / (A tot+B tot +C tot +D tot ) (5b)

[0069] F circuit =S 11 / S 21 =(B tot -C tot ) / 2 (5c)

[0070] Based on the above formula, S 11 and S 21 can be simplified as

[0071] |S 21 | 2 =1 / (1+|F circuit | 2 ) (6a)

[0072] |S 11 | 2 =|F circuit | 2 / (1+|F circuit | 2 ) (6b)

[0073] The S parameter response of the two filters proposed above can be accurately calculated by the above formula, and F circuit is the key point of the formula.

[0074] The impedances (Z1, Z2, Z3, Z ev , Z od ) of the two models are respectively brought into the above formulas (1)-(5) to calculate F circuit , and the following are respectively obtained:

[0075]

[0076]

[0077] p n and g n (n=0, 1, 2, 3, 4, 5, 7) are the power term coefficients corresponding to sin n θ, p n =f pn (Z1, Z2, Z3, Z ev , Z od ), g n =f gn (Z1, Z2, Z3, Z ev , Z od ), and the above formulas are all derived from the impedances (Z1, Z2, Z3, Z ev , Zod The function is composed of many parts, which are difficult to simplify. This step is to perform mathematical calculations on a PC using MATLAB software.

[0078] S can be obtained from the above formula. 11 and S 21 The point where the derivative is 0 is the frequency value corresponding to the highest point of each ripple (that is, the value of θ). Substituting this value into formula (6) yields S. 11 and S 21 The ripple height. This method can be used to constrain S. 11 and S 21 Given any ripple height (provided there is a mathematical solution), the corresponding circuit impedance value can be obtained.

[0079] Example

[0080] To verify the correctness of the formula, the in-band and out-of-band ripple of the two band-stop filters were controlled within -20dB as a constraint. The circuit parameters were then obtained using the formula, and the S-parameters of the resulting band-stop filters are as follows: Figures 3-4 As shown. The impedance values ​​of the two structures are as follows: for the forward coupled structures: Z1 = 25.8Ω, Z2 = 76.3Ω, Z3 = 72.9Ω, Z... ev =87.1Ω,Z od =59.9Ω. Reverse coupling structure: Z1 = 24.5Ω, Z2 = 77.9Ω, Z3 = 75.0Ω, Z... ev =109.7Ω,Z od =48.1Ω. (From) Figures 3-4 It can be seen that the forward-coupled circuit generates 8 reflection zeros and 4 transmission zeros, while the reverse-coupled structure generates 8 reflection zeros and 3 transmission zeros. Due to the presence of multiple transmission and reflection zeros, the filter exhibits excellent frequency selectivity. The passband and stopband are clearly distinguishable, contributing to the band-stop filtering characteristics. The significance of the constraint ripple at -20dB is that -20dB corresponds to one percent of the energy. A passband ripple (S11) of -20dB represents only one percent of the energy being reflected, with the rest of the signal passing through; while a stopband ripple (S21) of -20dB represents only one percent of the energy passing through, with the rest of the signal being reflected. This has significant implications for practical production applications, and the above results prove the accuracy of the theory.

[0081] Test case

[0082] To further verify the practical application value of the present invention, Figure 1 The forward-coupled circuit topology diagram was fabricated and tested. The circuit topology layout is as follows: Figure 5 As shown, the unit of length in the figure is mm. The experimentally manufactured board material is ROGERS. 5880, the dielectric constant of the plate material is 2.2, the plate thickness is 0.787 mm, and the copper thickness is 0.0175 mm. The leftmost end and the rightmost end correspond to port one and port two respectively, the length of the coupling line is 57.2 mm, the line width is 1.3 mm, and the coupling gap is 0.5 mm. The length of the transmission line Z1 is 53.2 mm, and the line width is 5.9 mm. The length of the transmission line Z2 is 55.0 mm, and the line width is 1.2 mm. In order to reduce the size of the circuit, the transmission line Z3 is bent to a certain extent, the line width is 1.2 mm, and the line length is 54.8 mm. The test results are in good agreement with the simulation results. The in-band and out-of-band ripple heights of the test results are very close to the simulation results, the frequency selectivity is good, and the number of transmission zeros is completely consistent. The number of reflection zeros of the test and simulation results (as shown in Figure 6 the figure) is one less than the mathematical calculation result. The reason is that in the actual situation, the transmission line and the coupling line will produce parasitic effects or exist dielectric loss at high frequencies, causing the S parameter to be inaccurate at high frequencies, which is unavoidable.

[0083] The ring-shaped band-stop filter with quasi-elliptic function response provided by the application can generate multiple transmission zeros and reflection zeros, realizes wide band-stop performance and good frequency selectivity, has very compact circuit size compared with other band-stop filters, and meets the miniaturization design requirement of the circuit. Meanwhile, the circuit is designed based on a planar circuit board material, and the preparation process is very convenient and low in price.

[0084] Although the embodiments of the application have been disclosed as above, it is not limited to the application listed in the specification and the embodiments, and can be applied to various fields suitable for the application. Those skilled in the art can easily realize other modifications, and therefore the application is not limited to specific details and the figures shown and described herein, without departing from the general concept defined by the claims and the equivalent scope.

Claims

1. A ring bandstop filter having a quasi-elliptic function response, characterized by Comprising: two source-end impedance units; a first branch connected between the two source-end impedance units; wherein the first branch comprises a first transmission line and two second transmission lines, and the first transmission line is connected between the two second transmission lines; a second branch in parallel with the first branch; wherein the second branch comprises a third transmission line and two coupling lines, and the third transmission line is connected between the two coupling lines.

2. The ring bandstop filter having a quasi-elliptic function response according to claim 1, characterized in that, The two coupling lines are forward coupling lines or reverse coupling lines.

3. The ring bandstop filter having a quasi-elliptic function response according to claim 2, characterized in that, The electrical lengths of the first transmission line, the second transmission line, the third transmission line and the coupling lines at a center frequency are all 90°.

4. A method of designing a ring bandstop filter having a quasi-elliptic function response, characterized by, A method for designing a ring band-stop filter with quasi-elliptic function response as claimed in any one of claims 1-3, comprising the following steps: Step one, determining the overall transmission matrix of the band-stop filter circuit; The overall transmission matrix is wherein A tot = (A up B down + A down B up ) / (B up + B down ) = D tot ; B tot = B up B down / (B up + B down ); C tot = (C up + C down ) + (A up - A down ) (D down - D up ) / (B up + B down ); where A up , B up , C up and D up are elements in the transmission matrix of the first branch, and A down , B down , C down and D down are elements in the transmission matrix of the second branch, respectively. Step two, obtaining the input reflection coefficient S of the band-reject filter circuit from the overall transmission matrix 11 and the forward transmission coefficient S 21 ; Step three, determining impedance values of the first transmission line, the second transmission line, the third transmission line and the coupling line corresponding to the constraint condition, with the constraint condition being the corrugation height of S 11 and S 21 .

5. The design method of a ring band-stop filter having a quasi-elliptic function response according to claim 4, characterized by, In the step two, the input reflection coefficient S is obtained by the following relation 11 and the forward transmission coefficient S 21 : S 11 = (B tot -C tot ) / (A tot +B tot +C tot +D tot ) S 21 = 2 / (A tot + B tot + C tot + D tot ) F circuit = S 11 / S 21 = (B tot - C tot ) / 2; where F circuit is the ratio function of S 11 and S 21 .

6. The design method of a ring band-stop filter having a quasi-elliptic function response according to claim 5, characterized by, When the two coupling lines are forward coupling lines: wherein, S represents the ratio of the two coupled lines when the two coupled lines are forward coupled 11 S 21 S n (n = 0, 1, 2, 3, 4, 5, 7) are coefficients of sin n θ.

7. The design method of a ring band-stop filter having a quasi-elliptic function response according to claim 5, characterized by, When the two coupling lines are reverse coupling lines: wherein, S represents the S parameter of the two coupled lines when the two coupled lines are forward coupled 11 S represents the S parameter of the two coupled lines when the two coupled lines are forward coupled 21 S represents the S parameter of the two coupled lines when the two coupled lines are forward coupled n (n = 0, 1, 2, 3, 4, 5, 7) are coefficients of the corresponding sin n θ.

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