Balanced linear phase bandpass filter with differential mode non-reflective characteristic

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By designing a balanced linear-phase bandpass filter with differential-mode non-reflective characteristics, and combining non-reflective absorption stubs and negative group delay stubs, the shortcomings of balanced filters in terms of non-reflection and linear phase are solved, achieving common-mode noise suppression and filter performance improvement.

CN116995383BActive Publication Date: 2026-07-21DALIAN MARITIME UNIVERSITY

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Patent Information

Authority / Receiving Office: CN · China
Patent Type: Patents(China)
Current Assignee / Owner: DALIAN MARITIME UNIVERSITY
Filing Date: 2023-08-25
Publication Date: 2026-07-21

AI Technical Summary

Technical Problem

There is limited research on the non-reflective and linear phase characteristics of existing balanced filters, making it difficult to achieve both non-reflective and linear phase functions while suppressing common-mode noise.

Method used

Design a balanced linear phase bandpass filter with differential-mode non-reflection characteristics. It employs a balanced differential input/output port, four quarter-wavelength impedance transformation lines, four quarter-wavelength microstrip transmission lines, four quarter-wavelength resonant microstrip lines, two quarter-wavelength inverted transformation lines, four sets of non-reflection absorption stubs, and two sets of negative group time delay stubs. The filter characteristics are adjusted by modifying each component.

Benefits of technology

It achieves differential-mode non-reflection characteristics, suppresses common-mode noise, improves electromagnetic compatibility characteristics, and reduces filter group delay ripple by negative group delay stubs, thereby achieving linear phase bandpass filtering characteristics and improving system performance.

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Abstract

The application discloses a balanced linear phase band-pass filter with a differential mode non-reflection characteristic, comprising a balanced differential input port A, a balanced differential output port B, four quarter-wavelength impedance transformation lines, four quarter-wavelength microstrip transmission lines, four quarter-wavelength resonant microstrip lines, two quarter-wavelength inverted transformation lines, four groups of non-reflection absorption branches, two groups of low-frequency negative group delay branches and two groups of high-frequency negative group delay branches. The balanced band-pass filter can be realized on a single PCB board, has a simple structure and is conducive to processing integration. In addition, the filter can not only effectively suppress common mode noise and improve the electromagnetic compatibility characteristics of a communication system, but also can effectively absorb out-of-band signals through resistance, reduce the reflected wave energy of the out-of-band signals, realize the differential mode non-reflection characteristic, and simultaneously load negative group delay branches to reduce the group delay fluctuation of the filter, realize the linear phase band-pass filtering characteristic and further improve the overall performance of the balanced band-pass filter.

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Description

Technical Field

[0001] This invention relates to a balanced bandpass filter, specifically a balanced linear phase bandpass filter with differential-mode non-reflection characteristics. Background Technology

[0002] Balanced circuits play a crucial role in modern wireless communication systems. Compared to unbalanced single-port input / output circuits, balanced circuits can efficiently suppress ambient noise and noise generated by internal active components, thus exhibiting superior electromagnetic compatibility characteristics. Various RF microwave devices, such as filters, mixers, and power amplifiers, are widely designed with balanced topologies. With the rapid development of integrated circuits, the demand for balanced devices will become even more urgent. Balanced filters possess filtering characteristics for differential-mode signal inputs while effectively suppressing common-mode noise. While balanced filters can be easily constructed using a single-port filter and two baluns, their size is enormous. Therefore, designing balanced filters as a single device without adding additional baluns is crucial and has broad application prospects.

[0003] Conventional filters are reflective filters, which achieve filtering by reflecting the energy of unwanted frequency components back to the signal source, thus achieving frequency selectivity. In nonlinear systems, the reflected echo signal mixes with the existing signal, generating numerous interference signals and significantly impacting system performance. To mitigate the negative effects of conventional filters, an attenuator is typically cascaded before the filter, followed by an amplifier, to minimize the impact of reflected signals. Non-reflective filters address the problems of conventional filters by effectively absorbing out-of-band signals through resistors and dissipating them as heat, reducing the reflected energy of out-of-band signals and improving overall system performance.

[0004] When evaluating the performance of a transmission system, it is usually necessary to analyze both its frequency domain and time domain characteristics simultaneously. The frequency domain characteristics analyzed include amplitude-frequency and phase-frequency characteristics. A good transmission system should not only have a flat amplitude-frequency characteristic but also a linear phase-frequency characteristic, that is, a flat group delay characteristic. With the continuous improvement of research and application of negative group delay technology, the negative group delay generated by the negative group delay circuit within a specific frequency band can be used to compensate for the bulges in the filter group delay fluctuation curve using external equalization design methods, without increasing the overall system delay, and achieving linear phase bandpass filtering characteristics.

[0005] However, most existing balanced filters focus on broadening the filter bandwidth, enhancing filter selectivity, and improving out-of-band rejection and common-mode rejection capabilities. Research on balanced non-reflective filters or balanced linear-phase filters is scarce. Therefore, it is of great significance to study balanced bandpass filters that achieve both common-mode rejection and non-reflective filtering, as well as the functional extension of linear phase. In view of this, it is indeed necessary to propose a balanced linear-phase bandpass filter with differential-mode non-reflective characteristics. Summary of the Invention

[0006] Based on this, in order to address the shortcomings of existing technologies, a balanced linear phase bandpass filter with differential-mode non-reflection characteristics is proposed.

[0007] Based on the above objectives, the technical solution of the present invention includes: a balanced differential input port A, a balanced differential output port B, four quarter-wavelength impedance transformation lines, four quarter-wavelength microstrip transmission lines, four quarter-wavelength resonant microstrip lines, two quarter-wavelength inverted transformation lines, four sets of non-reflection absorption stubs, two sets of low-frequency negative group delay stubs, and two sets of high-frequency negative group delay stubs.

[0008] The balanced differential input port A includes input port A+ and input port A. ; The balanced differential output port B includes output port B+ and output port B. ; The four quarter-wavelength impedance transformation lines include a first impedance transformation line, a second impedance transformation line, a third impedance transformation line, and a fourth impedance transformation line; wherein one end of the first impedance transformation line is connected to the input port A+, and the other end is connected to the first microstrip transmission line; one end of the second impedance transformation line is connected to the input port A+. One end of the third impedance transformation line is connected to the output port B+, and the other end is connected to the third microstrip transmission line; one end of the fourth impedance transformation line is connected to the output port B+. One end is connected to the first microstrip transmission line, and the other end is connected to the fourth microstrip transmission line. The four quarter-wavelength microstrip transmission lines include a first microstrip transmission line, a second microstrip transmission line, a third microstrip transmission line, and a fourth microstrip transmission line; wherein one end of the first microstrip transmission line is connected to a first impedance transformation line, and the other end is connected to the junction of a first resonant microstrip line and a first inverted transformation line; one end of the second microstrip transmission line is connected to a second impedance transformation line, and the other end is connected to the junction of a second resonant microstrip line and a second inverted transformation line; one end of the third microstrip transmission line is connected to a third impedance transformation line, and the other end is connected to the junction of a third resonant microstrip line and a first inverted transformation line; one end of the fourth microstrip transmission line is connected to a fourth impedance transformation line, and the other end is connected to the junction of a fourth resonant microstrip line and a second inverted transformation line. The four quarter-wavelength resonant microstrip lines include a first resonant microstrip line, a second resonant microstrip line, a third resonant microstrip line, and a fourth resonant microstrip line; wherein one end of the first resonant microstrip line is connected to the second resonant microstrip line, and the other end is connected to the junction of the first microstrip transmission line and the first inverted transformation line; one end of the second resonant microstrip line is connected to the first resonant microstrip line, and the other end is connected to the junction of the second microstrip transmission line and the second inverted transformation line; one end of the third resonant microstrip line is connected to the fourth resonant microstrip line, and the other end is connected to the junction of the third microstrip transmission line and the first inverted transformation line; one end of the fourth resonant microstrip line is connected to the third resonant microstrip line, and the other end is connected to the junction of the fourth microstrip transmission line and the second inverted transformation line. The two quarter-wavelength inverted transform lines include a first inverted transform line and a second inverted transform line; wherein one end of the first inverted transform line is connected to the junction of the first microstrip transmission line and the first resonant microstrip line, and the other end is connected to the junction of the third microstrip transmission line and the third resonant microstrip line; one end of the second inverted transform line is connected to the junction of the second microstrip transmission line and the second resonant microstrip line, and the other end is connected to the junction of the fourth microstrip transmission line and the fourth resonant microstrip line; The four sets of non-reflective absorbing stubs include a first non-reflective absorbing stub, a second non-reflective absorbing stub, a third non-reflective absorbing stub, and a fourth non-reflective absorbing stub; wherein the first non-reflective absorbing stub is connected to the connection between the first impedance transformation line and the first microstrip transmission line; the second non-reflective absorbing stub is connected to the connection between the second impedance transformation line and the second microstrip transmission line; the third non-reflective absorbing stub is connected to the connection between the third impedance transformation line and the third microstrip transmission line; and the fourth non-reflective absorbing stub is connected to the connection between the fourth impedance transformation line and the fourth microstrip transmission line. The first, second, third, and fourth non-reflective absorption stubs have the same structure. The first non-reflective absorption stub includes a non-reflective absorption transmission line, a non-reflective absorption open-circuit stub, and a non-reflective absorption resistor. One end of the non-reflective absorption transmission line is connected to the junction of the first impedance transformation line and the first microstrip transmission line, and the other end is connected to the junction of the non-reflective absorption open-circuit stub and the non-reflective absorption resistor. One end of the non-reflective absorption open-circuit stub is connected to the junction of the non-reflective absorption transmission line and the non-reflective absorption resistor, and the other end is open-circuited. One end of the non-reflective absorption resistor is connected to the junction of the non-reflective absorption transmission line and the non-reflective absorption open-circuit stub, and the other end is grounded. The two sets of low-frequency negative group delay stubs include a first low-frequency negative group delay stub and a second low-frequency negative group delay stub; wherein the first low-frequency negative group delay stub is connected to the connection between the first impedance transformation line and the first microstrip transmission line; and the second low-frequency negative group delay stub is connected to the connection between the second impedance transformation line and the second microstrip transmission line. The first low-frequency negative group delay stub and the second low-frequency negative group delay stub have the same structure; the first low-frequency negative group delay stub includes a low-frequency negative group delay transmission line, a low-frequency negative group delay short-circuit stub, and a low-frequency negative group delay absorption resistor; wherein one end of the low-frequency negative group delay transmission line is connected to the connection between the first impedance transformation line and the first microstrip transmission line, and the other end is connected to the connection between the low-frequency negative group delay short-circuit stub and the low-frequency negative group delay absorption resistor; one end of the low-frequency negative group delay short-circuit stub is connected to the connection between the low-frequency negative group delay transmission line and the low-frequency negative group delay absorption resistor, and the other end is grounded; one end of the low-frequency negative group delay absorption resistor is connected to the connection between the low-frequency negative group delay transmission line and the low-frequency negative group delay short-circuit stub, and the other end is grounded; The two sets of high-frequency negative group delay stubs include a first high-frequency negative group delay stub and a second high-frequency negative group delay stub; wherein the first high-frequency negative group delay stub is connected to the connection between the third impedance transformation line and the third microstrip transmission line; and the second high-frequency negative group delay stub is connected to the connection between the fourth impedance transformation line and the fourth microstrip transmission line. The first high-frequency negative group delay stub and the second high-frequency negative group delay stub have the same structure; the first high-frequency negative group delay stub includes a high-frequency negative group delay transmission line, a high-frequency negative group delay short-circuit stub, and a high-frequency negative group delay absorption resistor; wherein one end of the high-frequency negative group delay transmission line is connected to the connection between the third impedance transformation line and the third microstrip transmission line, and the other end is connected to the connection between the high-frequency negative group delay short-circuit stub and the high-frequency negative group delay absorption resistor; one end of the high-frequency negative group delay short-circuit stub is connected to the connection between the high-frequency negative group delay transmission line and the high-frequency negative group delay absorption resistor, and the other end is grounded; one end of the high-frequency negative group delay absorption resistor is connected to the connection between the high-frequency negative group delay transmission line and the high-frequency negative group delay short-circuit stub, and the other end is grounded.

[0009] Furthermore, the matching characteristics of the bandpass filter under differential-mode signal excitation are adjusted by modifying the first impedance transformation line, the second impedance transformation line, the third impedance transformation line, and the fourth impedance transformation line.

[0010] Furthermore, the filtering characteristics of the bandpass filter under differential-mode signal excitation are adjusted by modifying the first resonant microstrip line, the second resonant microstrip line, the third resonant microstrip line, and the fourth resonant microstrip line.

[0011] Furthermore, the non-reflection absorption characteristics of the bandpass filter are adjusted by modifying the first, second, third, and fourth non-reflection absorption stubs.

[0012] Furthermore, by adjusting the first low-frequency negative group delay stub and the second low-frequency negative group delay stub, the group delay fluctuation value in the low-frequency band of the bandpass filter is reduced.

[0013] Furthermore, by adjusting the first high-frequency negative group delay stub and the second high-frequency negative group delay stub, the group delay fluctuation value in the high-frequency band of the bandpass filter is reduced.

[0014] Compared with existing technologies, the balanced linear-phase bandpass filter with differential-mode anti-reflection characteristics disclosed in this application has the following advantages: To design a balanced filter as a single device and to address the shortcomings in current research on the functional extensions of balanced filters, such as anti-reflection and linear-phase characteristics, this invention provides a balanced linear-phase bandpass filter with differential-mode anti-reflection characteristics. This balanced bandpass filter can be implemented on a single PCB board, has a simple structure, and is conducive to fabrication and integration. Furthermore, this filter not only effectively suppresses common-mode noise and improves the electromagnetic compatibility of communication systems, but also effectively absorbs out-of-band signals through resistors, reducing the reflected wave energy of out-of-band signals and achieving differential-mode anti-reflection characteristics. Simultaneously, by loading negative group delay stubs, it reduces filter group delay ripple, achieving linear-phase bandpass filtering characteristics, thereby improving the overall performance of the balanced bandpass filter. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the structure of a balanced linear phase bandpass filter with differential mode reflection-free characteristics according to the present invention; Figure 2 This invention relates to a balanced linear-phase bandpass filter with differential-mode non-reflective characteristics, which is a hybrid filter excited by a differential-mode signal. S Parameter amplitude curve; Figure 3 This invention relates to a balanced linear-phase bandpass filter with differential-mode non-reflection characteristics, which is a hybrid filter under common-mode signal excitation. S Parameter amplitude curve; Figure 4 This is a comparison diagram of the group delay curves of a balanced linear phase bandpass filter with differential mode non-reflection characteristics according to the present invention, with and without negative group delay stubs. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0018] The present invention discloses a balanced linear phase bandpass filter with differential-mode non-reflection characteristics, characterized in that it comprises: a balanced differential input port A, a balanced differential output port B, four quarter-wavelength impedance transformation lines, four quarter-wavelength microstrip transmission lines, four quarter-wavelength resonant microstrip lines, two quarter-wavelength inverted transformation lines, four sets of non-reflection absorption stubs, two sets of low-frequency negative group delay stubs, and two sets of high-frequency negative group delay stubs; The balanced differential input port A includes input port A+1 and input port A. 2; The balanced differential output port B includes output port B+3 and output port B. 4; The four quarter-wavelength impedance transformation lines include a first impedance transformation line 5, a second impedance transformation line 6, a third impedance transformation line 7, and a fourth impedance transformation line 8; wherein one end of the first impedance transformation line 5 is connected to the input port A+1, and the other end is connected to the first microstrip transmission line 9; one end of the second impedance transformation line 6 is connected to the input port A... One end of the third impedance transformation line 7 is connected to the output port B+3, and the other end is connected to the third microstrip transmission line 11; one end of the fourth impedance transformation line 8 is connected to the output port B+3. The first end is connected to the fourth microstrip transmission line (phase 12), and the other end is connected to the fourth microstrip transmission line (phase 12). The four quarter-wavelength microstrip transmission lines include a first microstrip transmission line 9, a second microstrip transmission line 10, a third microstrip transmission line 11, and a fourth microstrip transmission line 12. One end of the first microstrip transmission line 9 is connected to the first impedance transformation line 5, and the other end is connected to the junction of the first resonant microstrip line 13 and the first inverted transformation line 17. One end of the second microstrip transmission line 10 is connected to the second impedance transformation line 6, and the other end is connected to the junction of the second resonant microstrip line 14 and the second inverted transformation line 18. One end of the third microstrip transmission line 11 is connected to the third impedance transformation line 7, and the other end is connected to the junction of the third resonant microstrip line 15 and the first inverted transformation line 17. One end of the fourth microstrip transmission line 12 is connected to the fourth impedance transformation line 8, and the other end is connected to the junction of the fourth resonant microstrip line 16 and the second inverted transformation line 18. The four quarter-wavelength resonant microstrip lines include a first resonant microstrip line 13, a second resonant microstrip line 14, a third resonant microstrip line 15, and a fourth resonant microstrip line 16. One end of the first resonant microstrip line 13 is connected to the second resonant microstrip line 14, and the other end is connected to the junction of the first microstrip transmission line 9 and the first inverted transformation line 17. One end of the second resonant microstrip line 14 is connected to the first resonant microstrip line 13, and the other end is connected to the junction of the second microstrip transmission line 10 and the second inverted transformation line 18. One end of the third resonant microstrip line 15 is connected to the fourth resonant microstrip line 16, and the other end is connected to the junction of the third microstrip transmission line 11 and the first inverted transformation line 17. One end of the fourth resonant microstrip line 16 is connected to the third resonant microstrip line 15, and the other end is connected to the junction of the fourth microstrip transmission line 12 and the second inverted transformation line 18. The two quarter-wavelength inverted transform lines include a first inverted transform line 17 and a second inverted transform line 18; wherein one end of the first inverted transform line 17 is connected to the connection between the first microstrip transmission line 9 and the first resonant microstrip line 13, and the other end is connected to the connection between the third microstrip transmission line 11 and the third resonant microstrip line 15; one end of the second inverted transform line 18 is connected to the connection between the second microstrip transmission line 10 and the second resonant microstrip line 14, and the other end is connected to the connection between the fourth microstrip transmission line 12 and the fourth resonant microstrip line 16; The four sets of non-reflective absorbing stubs include a first non-reflective absorbing stub 19, a second non-reflective absorbing stub 20, a third non-reflective absorbing stub 21, and a fourth non-reflective absorbing stub 22; wherein the first non-reflective absorbing stub 19 is connected to the connection between the first impedance transformation line 5 and the first microstrip transmission line 9; the second non-reflective absorbing stub 20 is connected to the connection between the second impedance transformation line 6 and the second microstrip transmission line 10; the third non-reflective absorbing stub 21 is connected to the connection between the third impedance transformation line 7 and the third microstrip transmission line 11; and the fourth non-reflective absorbing stub 22 is connected to the connection between the fourth impedance transformation line 8 and the fourth microstrip transmission line 12. The first non-reflective absorbing stub 19, the second non-reflective absorbing stub 20, the third non-reflective absorbing stub 21, and the fourth non-reflective absorbing stub 22 have the same structure; the first non-reflective absorbing stub includes a non-reflective absorbing transmission line 191, a non-reflective absorbing open-circuit stub 192, and a non-reflective absorbing resistor 193; one end of the non-reflective absorbing transmission line 191 is connected to the connection between the first impedance transformation line 5 and the first microstrip transmission line 9, and the other end is connected to the connection between the non-reflective absorbing open-circuit stub 192 and the non-reflective absorbing resistor 193; one end of the non-reflective absorbing open-circuit stub 192 is connected to the connection between the non-reflective absorbing transmission line 191 and the non-reflective absorbing resistor 193, and the other end is open-circuited; one end of the non-reflective absorbing resistor 193 is connected to the connection between the non-reflective absorbing transmission line 191 and the non-reflective absorbing open-circuit stub 192, and the other end is grounded; The two sets of low-frequency negative group delay stubs include a first low-frequency negative group delay stub 23 and a second low-frequency negative group delay stub 24; wherein the first low-frequency negative group delay stub 23 is connected to the connection between the first impedance transformation line 5 and the first microstrip transmission line 9; and the second low-frequency negative group delay stub 24 is connected to the connection between the second impedance transformation line 6 and the second microstrip transmission line 10. The first low-frequency negative group delay stub 23 and the second low-frequency negative group delay stub 24 have the same structure; the first low-frequency negative group delay stub 23 includes a low-frequency negative group delay transmission line 231, a low-frequency negative group delay short-circuit stub 232, and a low-frequency negative group delay absorption resistor 233; wherein one end of the low-frequency negative group delay transmission line 231 is connected to the connection between the first impedance transformation line 5 and the first microstrip transmission line 9, and the other end is connected to the connection between the low-frequency negative group delay short-circuit stub 232 and the low-frequency negative group delay absorption resistor 233; one end of the low-frequency negative group delay short-circuit stub 232 is connected to the connection between the low-frequency negative group delay transmission line 231 and the low-frequency negative group delay absorption resistor 233, and the other end is grounded; one end of the low-frequency negative group delay absorption resistor 233 is connected to the connection between the low-frequency negative group delay transmission line 231 and the low-frequency negative group delay short-circuit stub 232, and the other end is grounded; The two sets of high-frequency negative group delay stubs include a first high-frequency negative group delay stub 25 and a second high-frequency negative group delay stub 26; wherein the first high-frequency negative group delay stub 25 is connected to the connection between the third impedance transformation line 7 and the third microstrip transmission line 11; and the second high-frequency negative group delay stub 26 is connected to the connection between the fourth impedance transformation line 8 and the fourth microstrip transmission line 12. The first high-frequency negative group delay stub 25 and the second high-frequency negative group delay stub 26 have the same structure; the first high-frequency negative group delay stub 25 includes a high-frequency negative group delay transmission line 251, a high-frequency negative group delay short-circuit stub 252, and a high-frequency negative group delay absorption resistor 253; wherein one end of the high-frequency negative group delay transmission line 251 is connected to the connection between the third impedance transformation line 7 and the third microstrip transmission line 11, and the other end is connected to the connection between the high-frequency negative group delay short-circuit stub 252 and the high-frequency negative group delay absorption resistor 253; one end of the high-frequency negative group delay short-circuit stub 252 is connected to the connection between the high-frequency negative group delay transmission line 251 and the high-frequency negative group delay absorption resistor 253, and the other end is grounded; one end of the high-frequency negative group delay absorption resistor 253 is connected to the connection between the high-frequency negative group delay transmission line 251 and the high-frequency negative group delay short-circuit stub 252, and the other end is grounded.

[0019] Furthermore, the matching characteristics of the bandpass filter under differential mode signal excitation are adjusted by adjusting the first impedance transformation line 5, the second impedance transformation line 6, the third impedance transformation line 7, and the fourth impedance transformation line 8.

[0020] Furthermore, the filtering characteristics of the bandpass filter under differential mode signal excitation are adjusted by adjusting the first resonant microstrip line 13, the second resonant microstrip line 14, the third resonant microstrip line 15, and the fourth resonant microstrip line 16.

[0021] Furthermore, the non-reflection absorption characteristics of the bandpass filter are adjusted by modifying the first non-reflection absorption stub 19, the second non-reflection absorption stub 20, the third non-reflection absorption stub 21, and the fourth non-reflection absorption stub 22.

[0022] Furthermore, by adjusting the first low-frequency negative group delay stub 23 and the second low-frequency negative group delay stub 24, the group delay fluctuation value in the low-frequency band of the bandpass filter is reduced.

[0023] Furthermore, by adjusting the first high-frequency negative group delay stub 25 and the second high-frequency negative group delay stub 26, the group delay fluctuation value in the high-frequency band of the bandpass filter is reduced.

[0024] To further illustrate the balanced linear phase bandpass filter with differential mode non-reflection characteristics provided by the present invention, specific examples of implementation based on the technical solution of the present invention are described in detail below. However, the scope of protection of the present invention is not limited to the following embodiments, and the methods used in the following embodiments are conventional methods unless otherwise specified.

[0025] Specific example: This example illustrates a balanced linear-phase bandpass filter with differential-mode non-reflective characteristics. For example... Figure 2As shown, the input port reflection coefficient of a balanced linear phase bandpass filter with differential-mode non-reflection characteristics described in this invention at a center frequency of 2.45 GHz under differential-mode signal excitation is | S ddAA |for 24.4dB, output port reflection coefficient | S ddBB |for 22.4dB; Differential-mode transmission coefficient at the center frequency | S ddBA |for 1.63dB, 3dB differential mode transmission bandwidth is 850MHz; input differential mode reflection coefficient | S ddAA | Less than in the frequency range of 0.87~3.76GHz 10dB, the input differential-mode non-reflective absorption bandwidth is 3.40 times that of the 3dB differential-mode transmission bandwidth; the output differential-mode reflection coefficient | S ddBB | Smaller than 0.91~3.89GHz in the frequency range The 10dB differential-mode non-reflective absorption bandwidth at the output is 3.51 times that of the 3dB differential-mode transmission bandwidth, exhibiting broadband differential-mode non-reflective characteristics. For example... Figure 3 As shown, the balanced linear phase bandpass filter with differential-mode non-reflection characteristics described in this invention exhibits common-mode transmission suppression under common-mode signal excitation. S ccBA | Smaller than 1.77~3.11GHz in the frequency range 20dB, the common-mode rejection bandwidth is 1.58 times that of the 3dB differential-mode transmission bandwidth. For example... Figure 4 As shown, the group delay ripple within the passband of the balanced linear-phase bandpass filter with differential-mode non-reflection characteristics described in this invention is less than 0.15 ns when loaded with a negative group delay stub. This indicates that the balanced linear-phase bandpass filter with differential-mode non-reflection characteristics described in this invention not only suppresses common-mode noise and achieves non-reflection absorption of the differential-mode signal outside the passband, but also compensates for the convex portion of the filter's group delay ripple curve, thus realizing linear-phase bandpass filtering characteristics.

[0026] In summary, the balanced linear-phase bandpass filter with differential-mode non-reflection characteristics described in this invention not only effectively suppresses common-mode noise and exhibits superior electromagnetic compatibility, but also effectively absorbs out-of-band signals through resistors, reducing the reflected wave energy of out-of-band signals and achieving broadband differential-mode non-reflection characteristics. Simultaneously, by loading a negative group delay stub, the filter group delay ripple is reduced, realizing linear-phase bandpass filtering characteristics. Furthermore, the balanced linear-phase bandpass filter with differential-mode non-reflection characteristics described in this invention can be implemented on a single PCB board, has a simple structure, and is conducive to fabrication and integration. Therefore, it is very suitable for application in various balanced microwave systems to improve the overall system performance.

[0027] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the technical scope disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A balanced linear-phase bandpass filter with differential-mode non-reflective characteristics, characterized in that, include: Balanced differential input port A, balanced differential output port B, four quarter-wavelength impedance transformation lines, four quarter-wavelength microstrip transmission lines, four quarter-wavelength resonant microstrip lines, two quarter-wavelength inverted transformation lines, four sets of non-reflection absorption stubs, two sets of low-frequency negative group delay stubs, and two sets of high-frequency negative group delay stubs. The balanced differential input port A includes input port A+ (1) and input port A (2); The balanced differential output port B includes output port B+(3) and output port B. (4); The four quarter-wavelength impedance transformation lines include a first impedance transformation line (5), a second impedance transformation line (6), a third impedance transformation line (7), and a fourth impedance transformation line (8); wherein one end of the first impedance transformation line (5) is connected to the input port A+ (1), and the other end is connected to the first microstrip transmission line (9); one end of the second impedance transformation line (6) is connected to the input port A+ (1). (2) One end of the third impedance transformation line (7) is connected to the output port B+ (3), and the other end is connected to the third microstrip transmission line (11); one end of the fourth impedance transformation line (8) is connected to the output port B+ (3). (4) Connect one end to the other end and connect the other end to the fourth microstrip transmission line (12); The four quarter-wavelength microstrip transmission lines include a first microstrip transmission line (9), a second microstrip transmission line (10), a third microstrip transmission line (11), and a fourth microstrip transmission line (12); wherein one end of the first microstrip transmission line (9) is connected to the first impedance transformation line (5), and the other end is connected to the connection between the first resonant microstrip line (13) and the first inverted transformation line (17); one end of the second microstrip transmission line (10) is connected to the second impedance transformation line (6), and the other end is connected to the connection between the second resonant microstrip line (14) and the second inverted transformation line (18); one end of the third microstrip transmission line (11) is connected to the third impedance transformation line (7), and the other end is connected to the connection between the third resonant microstrip line (15) and the first inverted transformation line (17); one end of the fourth microstrip transmission line (12) is connected to the fourth impedance transformation line (8), and the other end is connected to the connection between the fourth resonant microstrip line (16) and the second inverted transformation line (18); The four quarter-wavelength resonant microstrip lines include a first resonant microstrip line (13), a second resonant microstrip line (14), a third resonant microstrip line (15), and a fourth resonant microstrip line (16); wherein one end of the first resonant microstrip line (13) is connected to the second resonant microstrip line (14), and the other end is connected to the junction of the first microstrip transmission line (9) and the first inverted transformation line (17); one end of the second resonant microstrip line (14) is connected to the first resonant microstrip line (13), The other end is connected to the connection between the second microstrip transmission line (10) and the second inverted transformation line (18); one end of the third resonant microstrip line (15) is connected to the fourth resonant microstrip line (16), and the other end is connected to the connection between the third microstrip transmission line (11) and the first inverted transformation line (17); one end of the fourth resonant microstrip line (16) is connected to the third resonant microstrip line (15), and the other end is connected to the connection between the fourth microstrip transmission line (12) and the second inverted transformation line (18); The two quarter-wavelength inverted transformation lines include a first inverted transformation line (17) and a second inverted transformation line (18); wherein one end of the first inverted transformation line (17) is connected to the connection between the first microstrip transmission line (9) and the first resonant microstrip line (13), and the other end is connected to the connection between the third microstrip transmission line (11) and the third resonant microstrip line (15); one end of the second inverted transformation line (18) is connected to the connection between the second microstrip transmission line (10) and the second resonant microstrip line (14), and the other end is connected to the connection between the fourth microstrip transmission line (12) and the fourth resonant microstrip line (16); The four sets of non-reflective absorbing stubs include a first non-reflective absorbing stub (19), a second non-reflective absorbing stub (20), a third non-reflective absorbing stub (21), and a fourth non-reflective absorbing stub (22); wherein the first non-reflective absorbing stub (19) is connected to the connection between the first impedance transformation line (5) and the first microstrip transmission line (9); the second non-reflective absorbing stub (20) is connected to the connection between the second impedance transformation line (6) and the second microstrip transmission line (10); the third non-reflective absorbing stub (21) is connected to the connection between the third impedance transformation line (7) and the third microstrip transmission line (11); and the fourth non-reflective absorbing stub (22) is connected to the connection between the fourth impedance transformation line (8) and the fourth microstrip transmission line (12). The first non-reflective absorbing stub (19), the second non-reflective absorbing stub (20), the third non-reflective absorbing stub (21), and the fourth non-reflective absorbing stub (22) have the same structure; the first non-reflective absorbing stub includes a non-reflective absorbing transmission line (191), a non-reflective absorbing open stub (192), and a non-reflective absorbing resistor (193); one end of the non-reflective absorbing transmission line (191) is connected to the connection between the first impedance transformation line (5) and the first microstrip transmission line (9), and the other end is connected to the connection between the non-reflective absorbing open stub (192) and the non-reflective absorbing resistor (193); one end of the non-reflective absorbing open stub (192) is connected to the connection between the non-reflective absorbing transmission line (191) and the non-reflective absorbing resistor (193), and the other end is open; one end of the non-reflective absorbing resistor (193) is connected to the connection between the non-reflective absorbing transmission line (191) and the non-reflective absorbing open stub (192), and the other end is grounded; The two sets of low-frequency negative group delay stubs include a first low-frequency negative group delay stub (23) and a second low-frequency negative group delay stub (24); wherein the first low-frequency negative group delay stub (23) is connected at the connection between the first impedance transformation line (5) and the first microstrip transmission line (9); the second low-frequency negative group delay stub (24) is connected at the connection between the second impedance transformation line (6) and the second microstrip transmission line (10); The first low-frequency negative group delay stub (23) and the second low-frequency negative group delay stub (24) have the same structure; the first low-frequency negative group delay stub (23) includes a low-frequency negative group delay transmission line (231), a low-frequency negative group delay short-circuit stub (232), and a low-frequency negative group delay absorption resistor (233); wherein one end of the low-frequency negative group delay transmission line (231) is connected to the connection between the first impedance transformation line (5) and the first microstrip transmission line (9), and the other end is connected to the low-frequency The connection point between the negative group delay short-circuit stub (232) and the low-frequency negative group delay absorption resistor (233); one end of the low-frequency negative group delay short-circuit stub (232) is connected to the connection point between the low-frequency negative group delay transmission line (231) and the low-frequency negative group delay absorption resistor (233), and the other end is grounded; one end of the low-frequency negative group delay absorption resistor (233) is connected to the connection point between the low-frequency negative group delay transmission line (231) and the low-frequency negative group delay short-circuit stub (232), and the other end is grounded; The two sets of high-frequency negative group delay stubs include a first high-frequency negative group delay stub (25) and a second high-frequency negative group delay stub (26); wherein the first high-frequency negative group delay stub (25) is connected to the connection between the third impedance transformation line (7) and the third microstrip transmission line (11); the second high-frequency negative group delay stub (26) is connected to the connection between the fourth impedance transformation line (8) and the fourth microstrip transmission line (12); The first high-frequency negative group delay stub (25) and the second high-frequency negative group delay stub (26) have the same structure; the first high-frequency negative group delay stub (25) includes a high-frequency negative group delay transmission line (251), a high-frequency negative group delay short-circuit stub (252), and a high-frequency negative group delay absorption resistor (253); wherein one end of the high-frequency negative group delay transmission line (251) is connected to the connection between the third impedance transformation line (7) and the third microstrip transmission line (11), and the other end is connected to the high-frequency negative group delay transmission line (26). The connection point between the high-frequency negative group delay short-circuit stub (252) and the high-frequency negative group delay absorption resistor (253); one end of the high-frequency negative group delay short-circuit stub (252) is connected to the connection point between the high-frequency negative group delay transmission line (251) and the high-frequency negative group delay absorption resistor (253), and the other end is grounded; one end of the high-frequency negative group delay absorption resistor (253) is connected to the connection point between the high-frequency negative group delay transmission line (251) and the high-frequency negative group delay short-circuit stub (252), and the other end is grounded.

2. A balanced linear-phase bandpass filter with differential-mode non-reflection characteristics according to claim 1, characterized in that: The matching characteristics of the bandpass filter under differential mode signal excitation are adjusted by adjusting the first impedance transformation line (5), the second impedance transformation line (6), the third impedance transformation line (7) and the fourth impedance transformation line (8).

3. A balanced linear-phase bandpass filter with differential-mode non-reflection characteristics according to claim 1, characterized in that: The filtering characteristics of the bandpass filter under differential mode signal excitation are adjusted by adjusting the first resonant microstrip line (13), the second resonant microstrip line (14), the third resonant microstrip line (15) and the fourth resonant microstrip line (16).

4. A balanced linear-phase bandpass filter with differential-mode non-reflection characteristics according to claim 1, characterized in that: The non-reflection absorption characteristics of the bandpass filter are adjusted by modifying the first non-reflection absorption stub (19), the second non-reflection absorption stub (20), the third non-reflection absorption stub (21), and the fourth non-reflection absorption stub (22).

5. A balanced linear-phase bandpass filter with differential-mode non-reflection characteristics according to claim 1, characterized in that: The group delay fluctuation value in the low-frequency band of the bandpass filter is reduced by adjusting the first low-frequency negative group delay stub (23) and the second low-frequency negative group delay stub (24).

6. A balanced linear-phase bandpass filter with differential-mode non-reflection characteristics according to claim 1, characterized in that: The group delay fluctuation value at the high frequency band within the passband of the bandpass filter is reduced by adjusting the first high-frequency negative group delay stub (25) and the second high-frequency negative group delay stub (26).