A compact balanced filter based on half circular patch resonators

Abstract

The application relates to a compact balanced filter based on a half-round patch resonator, which comprises a first rectangular dielectric substrate with an input feed line circuit layer arranged on the upper surface and a first half-round patch resonator arranged on the lower surface, a second rectangular dielectric substrate with a slotted floor arranged on the lower surface, a third rectangular dielectric substrate with empty layers arranged on the upper and lower surfaces, and a fourth rectangular dielectric substrate with a second half-round patch resonator arranged on the upper surface and an output feed line circuit layer arranged on the lower surface; the input feed line circuit layer comprises a first input port feed line and a second input port feed line; the output feed line circuit layer comprises a first output port feed line and a second output port feed line; during operation, a differential signal is input by the first input port feed line and the second input port feed line, the first half-round patch resonator is excited by electric coupling, resonance is generated, the resonance is coupled to the second half-round patch resonator through a rectangular etching slot line in the slotted floor, and then the resonance is coupled and output through the first output port feed line and the second output port feed line.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of microwave passive devices, and particularly relates to a compact balanced filter based on a half-round patch resonator. BACKGROUND

[0002] In recent years, the vigorous development of modern wireless communication systems has increased the demand for low-cost, small-sized, high-performance microwave devices. Among them, the balanced filter has always been the focus of the industry due to its working characteristics of differential mode transmission and common mode suppression, and is superior in environmental noise suppression, electromagnetic interference, and acoustic channel crosstalk. The balanced circuit system can improve the reliability of the system operation, and the filtering characteristics of the balanced filter improve the utilization rate of spectral resources to a certain extent, which has a great effect on the improvement of the overall performance of the system.

[0003] Document 1 (Z.-A. Ouyang, L. Zhu and L.-L. Qiu, "Wideband Balanced Filters With Intrinsic Common-Mode Suppression Using Coplanar Strip Double-Sided Shunt-Stub Structures," IEEE Transactions on Microwave Theory and Techniques, vol. 69, no. 8, pp. 3770-3782, Aug. 2021.) uses a mixed structure of microstrip lines, slot lines and coplanar striplines to design two balanced filters with wideband differential mode filtering response and common mode suppression. However, due to the wideband characteristics of the microstrip line to coplanar stripline transition structure, this method is usually difficult to achieve a narrowband filter response with high selectivity, and as the bandwidth increases, the overall level of common mode suppression is not high. At the same time, the power handling capacity of the circuit designed by the transmission line is lower than that of the patch type circuit.

[0004] Document 2 (Q. Liu, J. Wang, L. Zhu, G. Zhang, F. Huang and W. Wu, “A New Balanced Bandpass Filter With Improved Performance on Right-Angled Isosceles Triangular Patch Resonator,” IEEE Transactions on Microwave Theory and Techniques, vol. 66, no. 11, pp. 4803-4813, Nov. 2018.) utilizes the differential resonant mode of triangular patch resonator to design multiple balanced filters, which respectively realize the second-order, third-order and fifth-order Chebyshev filter responses. With the increase of the order, the frequency selectivity and common-mode rejection level of the balanced filter are improved, but the occupied area of the circuit also increases, which is not conducive to the miniaturization of the system design size, and there is a harmonic at the center frequency frequency multiplication, which is not suitable for multi-working system.

[0005] Document 3 (F. Huang, K. Aliqab, M. Hu and Y.-J. Zhu, “Design of a New Balanced Filter With Wideband DM Harmonic Elimination Based on Multilayer LCPLamination Technology,” 2022 IEEE MTT-S International Microwave Workshop Series on Advanced Materials and Processes for RF and THz Applications (IMWS-AMP), Guangzhou, China, 2022, pp. 1-3.) designs a dual-mode balanced filter with high out-of-band rejection level based on multilayer liquid crystal polymer (LCP) lamination technology using square patch resonator. Although this circuit achieves high level of common-mode rejection, the processing technology is relatively complex, and the circuit size is not advantageous in miniaturization.

[0006] Comprehensive current published papers and achievements can be found that the prior art is that the balanced filter designed by using the transmission line resonator can realize flexible filter response but the power handling capacity is not high, and the balanced filter based on the patch, waveguide and other resonators has large size and high power capacity handling ability, and the processing technology of part of the balanced filter with small size is relatively complex, which is not conducive to low-cost implementation of the system, in other words, the balanced filter design under the current technology cannot consider the size, high power capacity handling ability, good selectivity, high common mode suppression level and low cost, which is not conducive to popularization and application in modern wireless communication system. SUMMARY

[0007] The present application provides a compact balanced filter based on a semi-circular patch resonator to solve the problems in the prior art.

[0008] To achieve the above object, the present application adopts the following technical scheme:

[0009] A compact balanced filter based on a semi-circular patch resonator, comprising a first rectangular dielectric substrate, a second rectangular dielectric substrate, a third rectangular dielectric substrate and a fourth rectangular dielectric substrate; an input feed line circuit layer is arranged on the upper surface of the first rectangular dielectric substrate, and a first semi-circular patch resonator is arranged on the lower surface of the first rectangular dielectric substrate; a slotted floor is arranged on the lower surface of the second rectangular dielectric substrate, the upper and lower surfaces of the third rectangular dielectric substrate are empty layers, a second semi-circular patch resonator is arranged on the upper surface of the fourth rectangular dielectric substrate, and an output feed line circuit layer is arranged on the lower surface of the fourth rectangular dielectric substrate;

[0010] The input feed line circuit layer comprises a first input port feed line and a second input port feed line, and the first rectangular dielectric substrate is provided with a first metallized via and a second metallized via penetrating the first rectangular dielectric substrate; the first input port feed line is connected with the first semi-circular patch resonator through the first metallized via; and the second input port feed line is connected with the first semi-circular patch resonator through the second metallized via;

[0011] The middle part of the slotted floor is provided with an elongated rectangular etched slot line, and the center point of the rectangular etched slot line coincides with the center point of the slotted floor;

[0012] The output feed line circuit layer comprises a first output port feed line and a second output port feed line, and the fourth rectangular dielectric substrate is provided with a third metallized via and a fourth metallized via penetrating the fourth rectangular dielectric substrate, the first output port feed line is connected with the second semi-circular patch resonator through the third metallized via, and the second output port feed line is connected with the second semi-circular patch resonator through the fourth metallized via;

[0013] The first rectangular dielectric substrate, the second rectangular dielectric substrate, the third rectangular dielectric substrate and the fourth rectangular dielectric substrate are arranged from top to bottom in sequence to form a four-layer PCB board.

[0014] The differential signals are input by the first input port feed line and the second input port feed line respectively, and the first half-round patch resonator is excited to resonate by the electrical coupling, and the resonance is coupled to the second half-round patch resonator by the rectangular etched slot line in the slotted floor, and then coupled out by the first output port feed line and the second output port feed line.

[0015] To optimize the above technical solutions, the specific measures taken also include:

[0016] Further, the first input port feed line (01) includes a first microstrip line and a first quarter-wavelength impedance matching line.

[0017] One end of the first microstrip line is located as an input end at the edge of the long side of the first rectangular dielectric substrate, and the other end of the first microstrip line is connected with the first quarter-wavelength impedance matching line, and the layout of the first microstrip line and the first quarter-wavelength impedance matching line makes the first input port feed line L-shaped bending; the end of the first quarter-wavelength impedance matching line is connected with the first half-round patch resonator through the first metallized via hole;

[0018] The second input port feed line includes a second microstrip line and a second quarter-wavelength impedance matching line.

[0019] One end of the second microstrip line is located as an input end at the edge of the long side of the first rectangular dielectric substrate, and the other end of the second microstrip line is connected with the second quarter-wavelength impedance matching line, and the layout of the second microstrip line and the second quarter-wavelength impedance matching line makes the second input port feed line L-shaped bending; the end of the second quarter-wavelength impedance matching line is connected with the first half-round patch resonator through the second metallized via hole;

[0020] The first input port feed line and the second input port feed line are symmetrical about the symmetry plane of the first half-round patch resonator.

[0021] Further, the long symmetry axis of the rectangular etched slot line is located on the symmetry plane of the first half-round patch resonator.

[0022] Further, the first output port feed line includes a third microstrip line and a third quarter-wavelength impedance matching line.

[0023] One end of the third microstrip line guide strip is located as an output end at the edge of the long side of the fourth rectangular dielectric substrate, and the other end of the third microstrip line guide strip is connected with the third quarter-wavelength impedance matching line, and the layout of the third microstrip line guide strip and the third quarter-wavelength impedance matching line makes the first output port feed line L-shaped bending; the end of the third quarter-wavelength impedance matching line is connected with the second semicircular patch resonator through a third metallized via hole;

[0024] The second output port feed line includes a fourth microstrip line guide strip and a fourth quarter-wavelength impedance matching line, one end of the fourth microstrip line guide strip is located as an output end at the edge of the long side of the fourth rectangular dielectric substrate, and the other end of the fourth microstrip line guide strip is connected with the fourth quarter-wavelength impedance matching line, and the layout of the fourth microstrip line guide strip and the fourth quarter-wavelength impedance matching line makes the second output port feed line L-shaped bending; the end of the fourth quarter-wavelength impedance matching line is connected with the second semicircular patch resonator through a fourth metallized via hole;

[0025] The first output port feed line and the second output port feed line are symmetrical about the symmetry plane of the second semicircular patch resonator;

[0026] The symmetry plane of the first semicircular patch resonator and the symmetry plane of the second semicircular patch resonator are the same plane.

[0027] Further, the second semicircular patch resonator and the first semicircular patch resonator are center-symmetric about the center point of the slotted floor; the second output port feed line and the first input port feed line are rotationally symmetric about the center point of the slotted floor; and the first output port feed line and the second input port feed line are rotationally symmetric about the center point of the slotted floor.

[0028] Further, all the sizes of the first input port feed line, the second input port feed line, the first output port feed line and the second output port feed line are completely the same.

[0029] Further, the radius sizes of the first semicircular patch resonator and the second semicircular patch resonator are the same, and the radius size is determined according to the center frequency of the balanced filter and the TM 11 resonance mode of the semicircular patch resonator.

[0030] Further, the first quarter wavelength impedance matching line, the second quarter wavelength impedance matching line, the third quarter wavelength impedance matching line and the fourth quarter wavelength impedance matching line have the same size, and the total length of the impedance matching lines is a quarter of the wavelength calculated according to the center frequency of the balanced filter; the width of the impedance matching lines is set to adjust the difference between the resonant frequencies of the first half circular patch resonator and the second half circular patch resonator; the first microstrip line, the second microstrip line, the third microstrip line and the fourth microstrip line are all 50Ω microstrip lines.

[0031] Further, the first metallized via and the second metallized via are arranged at the connection positions of the first half circular patch resonator, and the third metallized via and the fourth metallized via are arranged at the connection positions of the second half circular patch resonator, so as to control the impedance matching and the out-of-band suppression level of the differential passband of the balanced filter.

[0032] Further, the length and width of the rectangular etched slot line are set to control the coupling strength between the first half circular patch resonator and the second half circular patch resonator, and further control the working bandwidth of the balanced filter.

[0033] The beneficial effects of the present application are:

[0034] Compared with the prior art, the present application has the advantages of compact size, high power capacity processing capability, good selectivity, high common mode suppression level and low cost, and the specific performances are:

[0035] (1) Compact size: the present application adopts the low-frequency resonant mode of the half circular patch resonator, and realizes the four-port circuit structure by using the multi-layer dielectric layer structure, so that the size without 50Ω microstrip line is about 0.26λ g ×0.53λ g

[0036] (2) High power capacity processing capability: the present application uses the patch resonator design, which has higher power capacity processing capability compared with the transmission line resonator.

[0037] (3) Good selectivity: the present application adopts the mode suppression feeding method and the floor slot coupling mode, which suppresses the generation of part of the harmonics, and the upper stopband suppression level is lower than 28.7dB in the frequency range of 3.08-6.36GHz.

[0038] (4) High common mode suppression level: the present application realizes the coupling of the two resonators by using the floor slot coupling mode, and simultaneously uses the differential mode resonant mode of the patch resonator and the differential mode transmission mode of the slot line resonator, which together improves the common mode suppression level of the balanced filter, and the common mode suppression level in the passband is as high as 62dB.

[0039] (5) Low cost: the multilayer PCB circuit of the application is designed, can be assembled through screws, the assembly effect is good, can reduce the production cost. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 It is the three-dimensional structure schematic diagram of the balanced filter of the application;

[0041] Figure 2 It is the circuit plan of each layer of the balanced filter of the application;

[0042] Figure 3 It is the structure size schematic diagram of the balanced filter in the embodiment of the application;

[0043] Figure 4 It is the mixed mode S parameter simulation curve diagram of the balanced filter in the embodiment of the application;

[0044] Wherein, 01-first input port feed line, 011-first microstrip line guide band, 012-first quarter wavelength impedance matching line, 013-first metallized via, 02-second input port feed line, 021-second microstrip line guide band, 022-second quarter wavelength impedance matching line, 023-second metallized via, 03-first half circular patch resonator, 04-slotted floor, 041-rectangular etched slot line, 05-second half circular patch resonator, 06-first output port feed line, 061-third microstrip line guide band, 062-third quarter wavelength impedance matching line, 063-third metallized via, 07-second output port feed line, 071-fourth microstrip line guide band, 072-fourth quarter wavelength impedance matching line, 073-fourth metallized via, 08-first rectangular dielectric substrate, 09-second rectangular dielectric substrate, 10-third rectangular dielectric substrate, 11-fourth rectangular dielectric substrate. DETAILED DESCRIPTION

[0045] The application will be further described in detail in combination with the drawings.

[0046] In an embodiment, the application provides a compact balanced filter based on a half circular patch resonator, comprising a first rectangular dielectric substrate 08 with an input feed line circuit layer arranged on the upper surface and a first half circular patch resonator 03 arranged on the lower surface, a second rectangular dielectric substrate 09 with only a slotted floor 04 arranged on the lower surface, a third rectangular dielectric substrate 10 with empty layers on the upper and lower surfaces, and a fourth rectangular dielectric substrate 11 with a second half circular patch resonator 05 arranged on the upper surface and an output feed line circuit layer arranged on the lower surface, wherein the input feed line circuit layer comprises a first input port feed line 01 and a second input port feed line 02, and the output feed line circuit layer comprises a first output port feed line 06 and a second output port feed line 07.

[0047] The first input port feed line 01 comprises a first microstrip line guide 011, a first quarter wavelength impedance matching line 012, and a first metallized via 013 located at the end of the first quarter wavelength impedance matching line 012 for connecting the first input port feed line 01 with the first semi-circular patch resonator 03, the front end of the first quarter wavelength impedance matching line 012 is connected with the end of the first microstrip line guide 011, and the input end of the first microstrip line guide 011 is located at the edge of the first rectangular dielectric substrate 08;

[0048] The second input port feed line 02 comprises a second microstrip line guide 021, a second quarter wavelength impedance matching line 022, and a second metallized via 023 located at the end of the second quarter wavelength impedance matching line 022 for connecting the second input port feed line 02 with the first semi-circular patch resonator 03, the front end of the first quarter wavelength impedance matching line 022 is connected with the end of the second microstrip line guide 021, and the input end of the second microstrip line guide 021 is located at the edge of the first rectangular dielectric substrate 08;

[0049] The first input port feed line 01 and the second input port feed line 02 are symmetrical about the symmetry plane of the first semi-circular patch resonator 03;

[0050] The first input port feed line 01 is L-shaped and bent, so that the input end of the first microstrip line guide 011 is located at the wide edge of the first rectangular dielectric substrate 08 for signal connection at the port.

[0051] The slotted floor 04 comprises an elongated rectangular etched slot line 041 located on the symmetry plane of the first semi-circular patch resonator 03 and arranged along the radial direction of the semicircle, and the centers of the two are the same.

[0052] The second semi-circular patch resonator 05 is symmetrical to the first semi-circular patch resonator 03 about the center point of the slotted floor 04.

[0053] The first output port feed line 06 comprises a third microstrip line guide 061, a third quarter wavelength impedance matching line 062, and a third metallized via 063 located at the front end of the third quarter wavelength impedance matching line 062 for connecting the first output port feed line 06 with the second semi-circular patch resonator 05, the end of the third quarter wavelength impedance matching line 062 is connected with the front end of the third microstrip line guide 061, and the output end of the third microstrip line guide 061 is located at the edge of the fourth rectangular dielectric substrate 11;

[0054] The second output port feed line 07 includes a fourth microstrip line guide 071, a fourth quarter wavelength impedance matching line 072, and a fourth metallized via 073 located at the front end of the fourth quarter wavelength impedance matching line 072 for connecting the second output port feed line 07 with the second half circular patch resonator 05, the end of the fourth quarter wavelength impedance matching line 072 is connected with the front end of the fourth microstrip line guide 071, and the output end of the fourth microstrip line guide 071 is located at the edge of the fourth rectangular dielectric substrate 11.

[0055] The first output port feed line 06 and the second output port feed line 07 are symmetrical about the symmetry plane of the second half circular patch resonator 05.

[0056] The second output port feed line 07 is rotationally symmetrical about the center point of the slotted floor 04 with the first input port feed line 01.

[0057] In the compact balanced filter based on the half circular patch resonator, the first half circular patch resonator 03 and the second half circular patch resonator 05 have the same radius size, the radius size determines the resonant frequency of the half circular patch resonator, and the TM 11 resonance mode of the resonator can determine the radius size, in the input and output port feed line, the first quarter wavelength impedance matching line 012, the second quarter wavelength impedance matching line 022, the third quarter wavelength impedance matching line 062 and the fourth quarter wavelength impedance matching line 072 have the same size, the total length of the impedance matching line is about one quarter of the wavelength at the center frequency, and the width of the impedance matching line can adjust the distance between the two resonant frequencies, the narrower the line width, the greater the resonant frequency distance, the wider the line width, the smaller the resonant frequency distance, and the port impedance cannot be matched when the line width is too wide or too narrow; the first metallized via 013 and the second metallized via 023 in the input port feed line are located at the position of the first half circular patch resonator 03, the third metallized via 063 and the fourth metallized via 023 in the output port feed line are located at the position of the second half circular patch resonator 05, which affects the input impedance of each harmonic position of the filter, the excited harmonics are different at different positions, and can be used for impedance matching adjustment and out-of-band suppression level regulation of the balanced filter differential passband; in addition, the length and width of the rectangular etched slot line 041 in the slotted floor 04 affect the coupling strength between the two resonators, and to a certain extent, control the working bandwidth of the balanced filter.

[0058] The working mechanism of the balanced filter is as follows: when a pair of differential signals is input by the first input port feed line 01 and the second input port feed line 02 respectively, the first semicircular patch resonator 03 is excited by electric coupling, the resonance is coupled to the second semicircular patch resonator 05 through the rectangular etched slot line 041 in the slotted floor 04, and then coupled out through the first output port feed line 06 and the second output port feed line 07, while when the common mode signal is input, the semicircular patch resonator resonant frequency is located at high frequency, and it is difficult to be coupled through the rectangular etched slot line 041, so that high level common mode suppression is realized at the differential mode working frequency.

[0059] The metal surface of the circuit substrate is processed and corroded by the printed circuit board manufacturing process in the manufacturing, so that the required metal pattern is formed, and the via hole is realized by the copper plating process, and the four-layer PCB can be assembled by screws, which is low in production cost and compact in structure. At the same time, the dual-mode filtering response is realized by using the semicircular patch resonator, which has wide stop band suppression and high level common mode suppression, and has large power capacity compared with the transmission line resonator. Since the balanced filter based on the semicircular patch resonator is simple in structure, compact in size, good in selectivity, wide in stop band suppression, and high in common mode suppression, it is suitable for modern wireless communication system.

[0060] The relative dielectric constant of the first rectangular dielectric substrate 8, the second rectangular dielectric substrate 9, the third rectangular dielectric substrate 10 and the fourth rectangular dielectric substrate 11 is 2.2, the thickness is 0.508 mm, and the loss tangent is 0.0009. According to the combination Figure 3 , the size parameters of the balanced filter are as follows: W1=2.95 mm, W2=2.1 mm, W d =1 mm, W s =0.9 mm, L1=10 mm, L2=10 mm, L s =11 mm, D=0.6 mm, W d = 1 mm, x via =24 mm, y via =10 mm, D patch =48 mm. The total area of the balanced filter including the 50Ω microstrip line guide is 38×48 mm 2 , and the corresponding guide wavelength size is about 0.42λ g ×0.53λ g , wherein λ g is the guide wave wavelength corresponding to the center frequency of the passband.

[0061] The balanced filter of the embodiment is modeled and simulated in the electromagnetic simulation software ANSYSEMSuite18.0. Figure 4The figure is the mixed mode S parameter simulation diagram of the balanced filter of the present example. It can be seen from the figure that the passband center frequency of the balanced filter is 2.4 GHz, the in-band return loss is less than -19.4 dB, the 3-dB relative bandwidth is 11.3%, the minimum insertion loss is 1.07 dB, the out-of-band harmonic suppression level is higher than 28.7 dB within 3.06-6.38 GHz, the in-band common mode suppression is better than 61 dB, and the common mode suppression level is higher than 33 dB within 0-6.48 GHz.

[0062] It should be noted that the terms such as "upper", "lower", "left", "right", "front", "back" and the like cited in the present application are only for the convenience of clear description, and are not intended to limit the scope of the present application. The change or adjustment of the relative relationship without substantial change of the technical content is also regarded as the scope of the present application.

[0063] The above is only the preferred embodiment of the present application, and the protection scope of the present application is not limited to the above-mentioned examples. Any technical solution falling within the concept of the present application is within the protection scope of the present application. It should be noted that, for ordinary skilled persons in the art, some improvements and refinements without departing from the principle of the present application are regarded as the protection scope of the present application.

Claims

1. A compact balanced filter based on a semi-circular patch resonator, characterized in that, The substrate includes a first rectangular dielectric substrate (08), a second rectangular dielectric substrate (09), a third rectangular dielectric substrate (10), and a fourth rectangular dielectric substrate (11). An input feed circuit layer is disposed on the upper surface of the first rectangular dielectric substrate (08), and a first semi-circular patch resonator (03) is disposed on the lower surface of the first rectangular dielectric substrate (08). A slotted ground plane (04) is disposed on the lower surface of the second rectangular dielectric substrate (09). The upper and lower surfaces of the third rectangular dielectric substrate (10) are empty layers. A second semi-circular patch resonator (05) is disposed on the upper surface of the fourth rectangular dielectric substrate (11), and an output feed circuit layer is disposed on the lower surface of the fourth rectangular dielectric substrate (11). The input feed circuit layer includes a first input port feed (01) and a second input port feed (02). The first rectangular dielectric substrate (08) is provided with a first metallized via (013) and a second metallized via (023) penetrating the first rectangular dielectric substrate (08). The first input port feed (01) is connected to the first semi-circular patch resonator (03) through the first metallized via (013). The second input port feed (02) is connected to the first semi-circular patch resonator (03) through the second metallized via (023). The grooved floor (04) has a slender rectangular etched groove (041) in the middle; the center point of the rectangular etched groove (041) coincides with the center point of the grooved floor (04); The output feed circuit layer includes a first output port feed (06) and a second output port feed (07). The fourth rectangular dielectric substrate (11) is provided with a third metallized via (063) and a fourth metallized via (073) penetrating the fourth rectangular dielectric substrate (11). The first output port feed (06) is connected to the second semi-circular patch resonator (05) through the third metallized via (063); the second output port feed (07) is connected to the second semi-circular patch resonator (05) through the fourth metallized via (073). The first rectangular dielectric substrate (08), the second rectangular dielectric substrate (09), the third rectangular dielectric substrate (10) and the fourth rectangular dielectric substrate (11) are arranged from top to bottom to form a four-layer PCB board; The differential signal is input from the first input port feed line (01) and the second input port feed line (02) respectively. The first semi-circular patch resonator (03) is excited by electrical coupling to generate resonance. After resonance, it is coupled to the second semi-circular patch resonator (05) through the rectangular etched groove line (041) in the slotted ground plane (04), and then coupled out through the first output port feed line (06) and the second output port feed line (07). The first input port feed (01) includes a first microstrip line conductor (011) and a first quarter-wavelength impedance matching line (012). One end of the first microstrip line conductor (011) is located at the edge of the long side of the first rectangular dielectric substrate (08) as the input terminal, and the other end of the first microstrip line conductor (011) is connected to the first quarter-wavelength impedance matching line (012). The arrangement of the first microstrip line conductor (011) and the first quarter-wavelength impedance matching line (012) makes the first input port feed line (01) bend in an L-shape. The end of the first quarter-wavelength impedance matching line (012) is connected to the first semi-circular patch resonator (03) through the first metallized via (013). The second input port feed (02) includes a second microstrip line conductor (021) and a second quarter-wavelength impedance matching line (022). One end of the second microstrip line conductor (021) is located at the edge of the long side of the first rectangular dielectric substrate (08) as the input terminal, and the other end of the second microstrip line conductor (021) is connected to the second quarter-wavelength impedance matching line (022). The layout of the second microstrip line conductor (021) and the second quarter-wavelength impedance matching line (022) makes the second input port feed line (02) bend in an L-shape. The end of the second quarter-wavelength impedance matching line (022) is connected to the first semi-circular patch resonator (03) through the second metallized via (023). The first input port feed (01) and the second input port feed (02) are symmetrical about the first semi-circular patch resonator (03); The first output port feed line (06) includes a third microstrip line conductor (061) and a third quarter-wavelength impedance matching line (062). One end of the third microstrip line conductor (061) is located at the edge of the long side of the fourth rectangular dielectric substrate (11) as the output terminal. The other end of the third microstrip line conductor (061) is connected to the third quarter-wavelength impedance matching line (062). The layout of the third microstrip line conductor (061) and the third quarter-wavelength impedance matching line (062) makes the first output port feed line (06) bend in an L-shape. The end of the third quarter-wavelength impedance matching line (062) is connected to the second semi-circular patch resonator (05) through the third metallized via (063). The second output port feed line (07) includes a fourth microstrip line conductor (071) and a fourth quarter-wavelength impedance matching line (072). One end of the fourth microstrip line conductor (071) serves as the output end and is located at the edge of the long side of the fourth rectangular dielectric substrate (11). The other end of the fourth microstrip line conductor (071) is connected to the fourth quarter-wavelength impedance matching line (072). The arrangement of the fourth microstrip line conductor (071) and the fourth quarter-wavelength impedance matching line (072) makes the second output port feed line (07) bend in an L-shape. The end of the fourth quarter-wavelength impedance matching line (072) is connected to the second semi-circular patch resonator (05) through a fourth metallized via (073). The first output port feed line (06) and the second output port feed line (07) are symmetrical about the second semi-circular patch resonator (05); The plane of symmetry of the first semi-circular patch resonator (03) and the plane of symmetry of the second semi-circular patch resonator (05) are the same plane.

2. The compact balanced filter based on a semi-circular patch resonator as described in claim 1, characterized in that, The long axis of symmetry of the rectangular etched groove (041) is located on the symmetry plane of the first semi-circular patch resonator (03).

3. The compact balanced filter based on a semi-circular patch resonator as described in claim 1, characterized in that, The second semi-circular patch resonator (05) and the first semi-circular patch resonator (03) are centrally symmetrical about the center point of the slotted floor (04); the second output port feed line (07) and the first input port feed line (01) are rotationally symmetrical about the center point of the slotted floor (04); the first output port feed line (06) and the second input port feed line (02) are rotationally symmetrical about the center point of the slotted floor (04).

4. The compact balanced filter based on a semi-circular patch resonator as described in claim 1, characterized in that, All dimensions of the first input port feed (01), the second input port feed (02), the first output port feed (06), and the second output port feed (07) are identical.

5. The compact balanced filter based on a semi-circular patch resonator as described in claim 1, characterized in that, The first semi-circular patch resonator (03) and the second semi-circular patch resonator (05) have the same radius. This is based on the center frequency of the balanced filter and the TM of the semi-circular patch resonator. 11 The resonant mode determines the radius dimension.

6. The compact balanced filter based on a semi-circular patch resonator as described in claim 1, characterized in that, The first quarter-wavelength impedance matching line (012), the second quarter-wavelength impedance matching line (022), the third quarter-wavelength impedance matching line (062), and the fourth quarter-wavelength impedance matching line (072) have the same size, and the total length of the impedance matching line is one-quarter of the wavelength calculated based on the center frequency of the balanced filter; the width of the impedance matching line is set to adjust the difference in resonant frequencies between the first semi-circular patch resonator (03) and the second semi-circular patch resonator (05); the first microstrip line conductor (011), the second microstrip line conductor (021), the third microstrip line conductor (061), and the fourth microstrip line conductor (071) are all 50 Ω microstrip line conductors.

7. The compact balanced filter based on a semi-circular patch resonator as described in claim 1, characterized in that, Set the connection positions of the first metallized via (013) and the second metallized via (023) with the first semi-circular patch resonator (03), set the connection positions of the third metallized via (063) and the fourth metallized via (023) with the second semi-circular patch resonator (05), and adjust the impedance matching and out-of-band suppression level of the differential passband of the balanced filter.

8. The compact balanced filter based on a semi-circular patch resonator as described in claim 1, characterized in that, The length and width of the rectangular etched groove (041) are set to control the coupling strength between the first semi-circular patch resonator (03) and the second semi-circular patch resonator (05), thereby controlling the operating bandwidth of the balanced filter.

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