Multi-mode reconfigurable microstrip line filter circuit

Abstract

The invention discloses a multi-mode reconfigurable microstrip line filter circuit, the whole circuit comprises 13 components including three ports, a section of quarter-wavelength parallel coupling line, seven sections of quarter-wavelength microstrip lines and two grounding resistors except for a control switch, and the sharing rate of the circuit components in four modes is up to 69.2%. The multi-zero-point band-pass filtering function, the non-reflection band-pass filtering function, the multi-zero-point band-stop filtering function and the non-reflection band-stop filtering function are integrated in a single circuit framework, the integration level is remarkably improved through a circuit resource sharing strategy, and efficient performance balance and state switching are achieved by optimizing transmission zero point distribution and circuit matching characteristics. Meanwhile, by optimizing the PIN diode switching network and the absorption branch design, reflection in the switching process is effectively reduced, the system stability is improved, and good impedance matching in the full frequency band is ensured. In addition, a multi-zero distribution optimization strategy is adopted, the out-of-band rejection capacity is improved, and a better signal screening effect is achieved.

Description

Technical Field

[0001] The present invention relates to a radio frequency communication device circuit, and more particularly to a microstrip line filter circuit. Background Art

[0002] As a core component in wireless communication, radar systems, and high-frequency electronic devices, microwave filters mainly function to achieve signal frequency selection and interference suppression. With the rapid development of 5G communication, millimeter-wave technology, and terahertz applications, modern high-frequency systems have put forward higher performance requirements for filters, including high frequency selectivity, strong out-of-band suppression, multi-mode support, and good system compatibility. However, due to their single function and fixed design, traditional filters are increasingly unable to meet the requirements of these complex application scenarios. In recent years, reconfigurable filters have gradually become a research hotspot due to their ability to flexibly switch between bandpass, bandstop, and other modes. By introducing adjustable elements such as PIN diodes and MEMS switches, these filters can achieve dynamic reconfiguration of multiple frequency responses to meet the application requirements of multiple frequency bands and multiple functions.

[0003] Nevertheless, existing reconfigurable filters still face many technical challenges in practical applications. First, the circuit designs in different modes are often independent, resulting in increased system complexity and difficulty in achieving efficient circuit resource reuse. Second, it is difficult to ensure the performance balance of multi-modal filters in different states, especially in the optimization of frequency selectivity and stopband suppression, where there are obvious trade-off problems. In addition, for high-performance systems, signal reflectionless transmission is an important requirement, but there are few filters in the existing technology that can simultaneously achieve reflectionless characteristics and multi-mode switching, limiting their promotion in high-demand applications. Finally, the non-ideal characteristics of switching elements (such as insufficient insertion loss and isolation) also significantly affect the overall performance of the filter and the stability of state switching. Summary of the Invention

[0004] Object of the Invention: Aiming at the above-mentioned existing technology, a multi-modal reconfigurable microstrip line filter circuit is proposed to achieve efficient switching among four modes: multi-zero bandpass, reflectionless bandpass, multi-zero bandstop, and reflectionless bandstop, while improving the circuit integration and ensuring high frequency selectivity, excellent stopband suppression, and reflectionless characteristics in each mode.

[0005] Technical solution: A multimodal reconfigurable microstrip line filter circuit, characterized by comprising: a quarter-wavelength parallel coupled line CL1, quarter-wavelength microstrip lines ML1 to ML7, resistors R1 and R2, and PIN diodes P1 to P7; the left lower end of the parallel coupled line CL1 is connected to port 1, and the right upper end is simultaneously connected to one ends of the PIN diodes P1 to P3 and one end of the microstrip line ML1, and the left upper end and the right lower end are in an open state; the other end of the microstrip line ML1 is connected to one end of the microstrip line ML2, and the other end of the microstrip line ML2 is open; the other end of the PIN diode P1 is grounded through the resistor R1, the other end of the PIN diode P2 is connected to port 2, and the other end of the PIN diode P3 is grounded; one ends of the microstrip lines ML3 and ML6 are simultaneously connected to the left lower end of the parallel coupling CL1, the other end of the microstrip line ML3 is connected to one end of the microstrip line ML4, the other end of the microstrip line ML4 is connected to one end of the microstrip line ML5 through the PIN diode P4, and the other ends of the microstrip line ML5 and the microstrip line ML6 are simultaneously connected to one ends of the microstrip line ML7, the PIN diode P5, and the PIN diode P6; the other end of the microstrip line ML7 is grounded through the PIN diode P7; the other end of the PIN diode P5 is connected to port 3, and the other end of the PIN diode P6 is grounded through the resistor R2; wherein, the microstrip lines ML1 and ML2 with different impedances form a half-wavelength stepped impedance microstrip line, and the microstrip lines ML3 and ML4 with different impedances form a half-wavelength stepped impedance microstrip line; the microstrip lines ML3, ML4, ML5, and ML6 form a square loop structure.

[0006] Furthermore, the switching of four modes of the filter circuit is realized by controlling the on / off of the PIN diodes P1 to P7; wherein, Mode 1: Control the PIN diodes P2 and P7 to conduct, and P1 and P3 to P6 to be disconnected, forming a multi-transmission zero bandpass filter; Mode 2: Control the PIN diodes P2, P4, and P6 to conduct, and P1, P3, P5, and P7 to be disconnected, forming a full-band reflectionless bandpass filter; Mode 3: Control the PIN diodes P3, P4, and P5 to conduct, and P1, P2, P6, and P7 to be disconnected, forming a multi-zero bandstop filter; Mode 4: Control the PIN diodes P1, P4, and P5 to conduct, and P2, P3, P6, and P7 to be disconnected, forming a full-band reflectionless bandstop filter.

[0007] Beneficial effects: Although existing switchable microstrip line filters can switch between different filtering modes (such as band-pass and band-stop) through switching elements, there are still obvious disadvantages and problems. First, in most designs, different modes are often implemented by independent circuits, resulting in poor circuit resource reusability, a significant increase in system complexity and volume. Second, the performance balance under different filtering modes is relatively poor. Especially in high-frequency applications, it is difficult to optimize both frequency selectivity and stopband suppression simultaneously. In some modes, there may even be problems such as large insertion loss or insufficient stopband suppression. In addition, existing filter designs pay less attention to the reflectionless characteristic, which is likely to introduce signal reflection, leading to multipath interference or performance degradation in the system.

[0008] In view of the problems faced by traditional filters, such as resource waste, unbalanced performance, and lack of reflectionless characteristic, the present invention proposes a multi-modal reconfigurable microstrip line filter circuit. Through innovative design, the multi-zero band-pass, reflectionless band-pass, multi-zero band-stop, and reflectionless band-stop filtering functions are integrated into a single circuit architecture. By using a circuit resource sharing strategy, the integration degree is significantly improved, and through optimizing the distribution of transmission zeros and circuit matching characteristics, efficient performance balance and state switching are achieved. This design provides a new idea for the research and development of multi-functional and high-performance filters, and is of great significance to the development of future high-frequency communication and radar systems.

[0009] Specifically, through ingenious construction and optimizing the circuit topology and switching mechanism, the efficient integration of four modal circuits is realized. The whole circuit consists of 13 components including three ports, a quarter-wavelength parallel coupled line, seven quarter-wavelength microstrip lines, and two grounded resistors except for the control switches. Among them, the common part of the circuit in four modes includes port 1, a quarter-wavelength parallel coupled line, and seven quarter-wavelength microstrip lines, a total of 9 components, and the sharing rate is as high as 69.2%. This avoids the disadvantages of traditional reconfigurable filters that require multiple independent circuits to implement different modes, improves the circuit integration degree and reduces the circuit area.

[0010] By optimizing the transmission path and matching network, and adopting a specific parallel coupled microstrip line structure and absorbing stub design, it is ensured that the filter can effectively eliminate out-of-band reflection in the reflectionless mode of the whole frequency band, improving the system stability.

[0011] When the signal is output from port 2, for the filtering from port 1 to port 3, there are two switching states. One can be used as the complementary stub of band-pass filtering, dissipating out-of-band signals through the resistor to achieve the reflectionless function of the whole frequency band; the other can be used as the stub to generate two pairs of transmission zeros, improving the stopband suppression and frequency selection pattern of band-pass filtering.

[0012] When the signal is output from port 3, for ports 1 to 2, there are also two switching states. One is to connect to the grounding resistor R1 to form a complementary stub for band-stop filtering, achieving the function of no reflection in the full frequency band; the other is to act as a stub to generate a pair of transmission zeros, enhancing the stopband suppression and frequency selection characteristics. Description of the Drawings

[0013] Figure 1 It is a schematic diagram of the circuit structure of a multimode reconfigurable microstrip line filter; Figure 2 It is a circuit diagram of the effects of four switching modes, where (a) is a multi-zero bandpass filter, (b) is a full-band non-reflective bandpass filter, (c) is a multi-zero bandstop filter, and (d) is a full-band non-reflective bandstop filter; Figure 3 It is a schematic diagram of the parameters of a multimode reconfigurable microstrip line filter; Figure 4 It is a frequency response curve diagram of the four switching mode states in this embodiment, where (a) is Mode 1: multi-zero bandpass filter, (b) is Mode 2: full-band non-reflective bandpass filter, (c) is Mode Three: multi-zero bandstop filter, and (d) is Mode Four: full-band non-reflective bandstop filter. Detailed Embodiment

[0014] The following further explains the present invention with reference to the drawings.

[0015] This embodiment proposes a multimode reconfigurable microstrip line filter, which realizes the efficient switching of four modes, namely a multi-zero bandpass filter, a full-band non-reflective bandpass filter, a multi-zero bandstop filter, and a full-band non-reflective bandstop filter, through ingenious construction, optimization of the circuit topology and switching mechanism, and the filtering responses of the four states all have high frequency selectivity and excellent stopband suppression effects.

[0016] As Figure 1 shown, a multimode reconfigurable microstrip line filter circuit in this embodiment includes: port 1, port 2, port 3, a quarter-wavelength parallel coupled line CL1, quarter-wavelength microstrip lines ML1 to ML7, resistor R1, resistor R2, and PIN diodes P1 to P7.

[0017] The left lower end of the parallel coupled line CL1 is connected to port 1, and the right upper end is simultaneously connected to one end of PIN diodes P1 to P3 and one end of the microstrip line ML1. The left upper end and the right lower end are in an open state. The other end of the microstrip line ML1 is connected to one end of the microstrip line ML2, and the other end of the microstrip line ML2 is open. The other end of PIN diode P1 is grounded through resistor R1, the other end of PIN diode P2 is connected to port 2, and the other end of PIN diode P3 is grounded. One end of the microstrip line ML3 and one end of the microstrip line ML6 are simultaneously connected to the left lower end of the parallel coupled CL1. The other end of the microstrip line ML3 is connected to one end of the microstrip line ML4. The other end of the microstrip line ML4 is connected to one end of the microstrip line ML5 through PIN diode P4. The other end of the microstrip line ML5 and the other end of the microstrip line ML6 are simultaneously connected to one end of the microstrip line ML7, PIN diode P5, and PIN diode P6. The other end of the microstrip line ML7 is grounded through PIN diode P7. The other end of PIN diode P5 is connected to port 3, and the other end of PIN diode P6 is grounded through resistor R2.

[0018] In the above circuit, the semiconductor PIN diodes P1 to P7 are all controlled by controlling the supply voltage of the RF switch to achieve four-mode switching.

[0019] Mode 1: Multi-transmission zero bandpass filter, in which PIN diodes P2 and P7 are turned on, and P1 and P3 to P6 are turned off. The circuit of the multi-transmission zero bandpass filter is as Figure 2 shown in (a). It can be seen from the figure that the signal is input from port 1, and after passing through the quarter-wavelength parallel coupled line CL1, a filtering effect is generated. The half-wavelength stepped impedance microstrip line composed of the microstrip lines ML1 and ML2 with different impedances generates a pair of transmission zeros on both sides of the passband. The half-wavelength stepped impedance microstrip line composed of the microstrip lines ML3 and ML4 with different impedances generates a second pair of transmission zeros. The T-shaped connected microstrip lines ML5, ML6, and the grounded microstrip line ML7 generate a third pair of transmission zeros, and finally, it is output from port 2.

[0020] Mode 2: Full-band reflectionless bandpass filter, in which PIN diodes P2, P4, and P6 are turned on, and P1, P3, P5, and P7 are turned off. The circuit of the full-band reflectionless bandpass filter is as Figure 2As shown in (b), the quarter-wavelength parallel-coupled line CL1 and the half-wavelength stepped-impedance microstrip line composed of microstrip lines ML1 and ML2 can still form filtering, and there is a pair of transmission zeros on both sides of the passband. The out-of-band reflected signal will flow through the absorbing stub below the circuit, where the microstrip line ML6 constitutes branch 1, and the microstrip lines ML3, ML4, and ML5 constitute branch 2. The microstrip lines ML3, ML4, ML5, and ML6 form a square loop structure. The electrical lengths of the three sections of the microstrip lines ML3 to ML5 are 270 degrees. Due to the 180-degree phase difference between branch 1 and branch 2, the out-of-band signal is canceled and then dissipated through the resistor R2. Here, the open microstrip line ML7 effectively improves the out-of-band reflection-free level.

[0021] Mode 3: Multi-zero band-stop filter, in which the PIN diodes P3, P4, and P5 are turned on, and P1, P2, P6, and P7 are turned off. The circuit of the multi-zero band-stop filter is as Figure 2 shown in (c). At this time, due to the 180-degree phase difference between branch 1 and branch 2 and the existence of the stepped impedance, the signal flowing through the square loop structure will be canceled and will not be transmitted to port 3, and there are two transmission zeros. In addition, the open microstrip line ML7 will generate a transmission zero at the center frequency point. The half-wavelength stepped-impedance microstrip line composed of the microstrip lines ML1 and ML2 is short-circuited and does not affect filtering. After the right upper end of the quarter-wavelength parallel-coupled line CL1 is grounded, a second pair of transmission zeros is generated. Finally, a band-stop filter with five transmission zeros is formed.

[0022] Mode 4: All-band reflection-free band-stop filter, at this time the PIN diodes P1, P4, and P5 are turned on, and P2, P3, P6, and P7 are turned off. The circuit of the all-band reflection-free band-stop filter is as Figure 2 shown in (d). In addition to the microstrip lines ML3, ML4, ML5, ML6, and ML7 generating a stopband filter with three transmission zeros, the grounding resistor R1 connected to the right upper end of the quarter-wavelength parallel-coupled line CL1 can generate a complementary passband and dissipate the energy reflected by the stopband through the resistor R1. At this time, the half-wavelength stepped-impedance microstrip line composed of the microstrip lines ML1 and ML2 can effectively improve the absorption level of the reflected signal.

[0023] Figure 3 This is the parameter schematic diagram of the multi-mode reconfigurable microstrip line filter with a center frequency of 2 GHz in this embodiment. The specific parameters are: Z e = 205.2 Ω, Z o = 105.3 Ω, Z1 = 116.35 Ω, Z2 = 163.36 Ω, Z3 = 171.1 Ω, Z4 = 148.1Ω, Z5 = 148.1 Ω, Z6 = 133.8 Ω, Z7 = 177.3 Ω, R1 = R2 = 50 Ω. Model and simulate with simulation software to obtain Figure 4Frequency response curves of four switching states.

[0024] The multi-zero bandpass filtering response of Mode 1 is as Figure 4 shown in (a) of, the 3-dB relative bandwidth is 63%, three transmission poles are generated within the passband, and three transmission zeros are respectively located outside the passband, resulting in a stopband rejection better than 19 dB outside the band.

[0025] The full-band reflectionless bandpass filtering response of Mode 2 is as Figure 4 shown in (b) of, the 3-dB relative bandwidth is 63%, and the reflection coefficient S 11 across the entire frequency band (0 - 4 GHz) is less than -23 dB.

[0026] The multi-zero bandstop filtering response of Mode 3 is as Figure 4 shown in (c) of, the 3-dB relative bandwidth is 56%, five transmission zeros are generated within the stopband, and the stopband rejection is better than 26 dB.

[0027] The full-band reflectionless bandstop filtering response of Mode 4 is as Figure 4 shown in (d) of, and the reflection coefficient S 11 across the entire frequency band (0 - 4 GHz) is less than -23 dB.

[0028] Compared with existing reconfigurable microstrip filters, the present invention has higher integration and mode switching capabilities, realizing four modes of multi-zero bandpass, reflectionless bandpass, multi-zero bandstop, and reflectionless bandstop within the same circuit architecture, significantly improving the utilization rate of circuit resources. At the same time, by optimizing the PIN diode switching network and absorption stub design, the present invention effectively reduces reflections during switching, improves system stability, and ensures good impedance matching across the entire frequency band. In addition, by adopting a multi-zero distribution optimization strategy, the out-of-band rejection ability is enhanced, achieving a better signal screening effect; combined with an efficient mode switching mechanism, the application flexibility is greatly improved, making it suitable for scenarios such as 5G / 6G radio frequency front-ends. Overall, the present invention is superior to the prior art in terms of integration, out-of-band rejection, reflectionless characteristics, and high-frequency adaptability, providing an innovative solution for the design of high-performance filters.

[0029] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A multi-mode reconfigurable microstrip line filter circuit, characterized in that: include: A quarter-wavelength parallel coupled line CL1, a quarter-wavelength microstrip line ML1~ML7, a resistor R1, a resistor R2 and PIN transistors P1~P7; The lower left end of the parallel coupling line CL1 is connected to port 1, and the upper right end is connected to one end of PIN tubes P1~P3 and one end of microstrip line ML1 at the same time, and the upper left end and the lower right end are in an open circuit state; the other end of microstrip line ML1 is connected to one end of microstrip line ML2, and the other end of microstrip line ML2 is open circuit; the other end of PIN tube P1 is grounded through resistor R1, the other end of PIN tube P2 is connected to port 2, and the other end of PIN tube P3 is grounded; one end of microstrip line ML3 and microstrip line ML6 are connected to the lower left end of parallel coupling CL1 at the same time, the other end of microstrip line ML3 is connected to one end of microstrip line ML4, the other end of microstrip line ML4 is connected to one end of microstrip line ML5 through PIN tube P4, the other end of microstrip line ML5 and the other end of microstrip line ML6 are connected to one end of microstrip line ML7, PIN tube P5, and PIN tube P6 at the same time; the other end of microstrip line ML7 is grounded through PIN tube P7; the other end of PIN tube P5 is connected to port 3, and the other end of PIN tube P6 is grounded through resistor R2; Among them, microstrip lines ML1 and ML2 with different impedances form a half-wavelength step impedance microstrip line, and microstrip lines ML3 and ML4 with different impedances form a half-wavelength step impedance microstrip line; microstrip lines ML3, ML4, ML5 and ML6 form a square ring structure.

2. The multi-mode reconfigurable microstrip line filter circuit according to claim 1, characterized in that: The switching of the filter circuit into four modes is realized by controlling the on and off of the PIN tubes P1~P7; wherein, mode 1: the PIN tubes P2 and P7 are controlled to be turned on, and P1 and P3~P6 are turned off, so as to form a multi-transmission zero-point bandpass filter; mode 2: the PIN tubes P2, P4 and P6 are controlled to be turned on, and P1, P3, P5 and P7 are turned off, so as to form a full-band reflection-free bandpass filter; mode 3: the PIN tubes P3, P4 and P5 are controlled to be turned on, and P1, P2, P6 and P7 are turned off, so as to form a multi-zero-point bandstop filter; mode 4: the PIN tubes P1, P4, P5 are controlled to be turned on, and P2, P3, P6 and P7 are turned off, so as to form a full-band reflection-free bandstop filter.

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