A passband flat reconfigurable filter attenuator based on lossy synthesis

Abstract

The application provides a passband flat reconfigurable filter attenuator based on lossy synthesis, and belongs to the technical field of radio frequency front ends of wireless communication systems.The filter attenuator is a four-order filter with a cascade quadruplet structure, and adopts a symmetrical structure; the filter attenuator comprises input port impedance, output port impedance, input port series resistance, output port series resistance, two first capacitors, two first resistors, two first inductors, two second capacitors, two second inductors, two inter-stage coupling capacitors, a cross-coupling capacitor and an inter-stage coupling inductor; the first capacitor, the first resistor and the first inductor are connected in parallel to form an adjustable parallel LC resonator, and the second capacitor and the second inductor are connected in parallel to form a lossless parallel LC resonator. The application directly introduces the attenuation amount into the filter synthesis process based on the lossy filter synthesis theory, realizes the integrated design of the filter and the adjustable attenuation function, and can realize continuous filter attenuation reconfiguration.

Description

Technical Field

[0001] This invention belongs to the field of radio frequency front-end technology of wireless communication systems, and particularly relates to a passband flat reconfigurable filter attenuator based on lossy synthesis. Background Technology

[0002] Filters and attenuators are essential functional components in wireless communication, software-defined radio, phased array radar, and reconfigurable RF front-ends. Traditional solutions typically cascade bandpass filters and variable attenuators, which, while enabling frequency selection and amplitude control respectively, increase circuit size, interconnect losses, and matching network complexity, hindering the development of RF front-ends towards high integration, miniaturization, and multifunctionality.

[0003] To integrate filtering and attenuation functions into a single device, existing technologies employ semiconductor processes, graphene, varactor diodes, and PIN diodes to realize adjustable filter attenuators. Among these, the scheme using PIN diodes or varactor diodes has advantages such as flexible implementation and ease of integration with microstrip or lumped circuits. However, traditional designs typically focus on changing a single loss element or local parameters. When the attenuation increases, it can easily cause changes in port matching, resonant frequency, coupling strength, and transmission zero position, resulting in problems such as increased passband ripple, decreased selectivity, or deterioration of return loss.

[0004] While existing direct synthesis or empirical optimization methods can expand the attenuation adjustment range, they lack a unified theoretical constraint on how to rationally distribute losses within the filter network under different attenuation states. Therefore, a design method is needed that directly introduces the target attenuation amount during the lossy synthesis stage of the filter and maps the lossy network parameters corresponding to different attenuation states to the same adjustable circuit. This method would enable the device to maintain a flat passband amplitude-frequency response, stable transmission zeros, and good return loss during continuous attenuation adjustment. Summary of the Invention

[0005] The purpose of this invention is to provide a passband flat reconfigurable filter attenuator based on lossy synthesis. This filter attenuator utilizes lossy coupling matrix synthesis theory to directly introduce the target attenuation into the filter synthesis process. It also coordinates and adjusts the port resistance, resonator loss, and coupling parameters according to the lossy network parameters corresponding to different attenuation states, enabling the filter to maintain a flat passband amplitude-frequency response, good return loss, and stable transmission zero position during a wide range of attenuation adjustment. This solves the technical problems of increased passband fluctuations, decreased selectivity, or deteriorated return loss in existing filter attenuators.

[0006] To solve the above-mentioned technical problems, the specific technical solution of the present invention is as follows:

[0007] A passband flat reconfigurable filter attenuator based on lossy synthesis, the filter attenuator including input port impedance Output port impedance Input port series resistor Output port series resistor Two first capacitors Two first resistors Two first inductors Two second capacitors Two second inductors Two interstage coupling capacitors Cross-coupling capacitors and interstage coupling inductors ;

[0008] Input port impedance One end is grounded, and the other end is connected to the input port series resistor. One end is used as the input terminal; a resistor is connected in series at the input port. The other end is connected to a cross-coupling capacitor. One end, the first interstage coupling capacitor One end of the first adjustable parallel LC resonator; the other end of the first adjustable parallel LC resonator is grounded; the first interstage coupling capacitor. The other end is connected to the interstage coupling inductor. One end of the first lossless parallel LC resonator; the other end of the first lossless parallel LC resonator is grounded; interstage coupling inductor. The other end is connected to the second interstage coupling capacitor. One end of the second lossless parallel LC resonator; the other end of the second lossless parallel LC resonator is grounded; the second interstage coupling capacitor. The other end is connected to a cross-coupling capacitor. The other end, the output port series resistor One end of the second adjustable parallel LC resonator; the other end of the second adjustable parallel LC resonator is grounded; the output port is connected in series with a resistor. The other end is connected to the output port impedance. One end; output port impedance The other end is grounded as the output port.

[0009] Furthermore, both the first adjustable parallel LC resonator and the second adjustable parallel LC resonator are composed of a first capacitor. First resistor and the first inductor Both the first and second lossless parallel LC resonators are formed by connecting them in parallel, and both are composed of a second capacitor. and the second inductor They are connected in parallel.

[0010] Furthermore, the input port series resistor Output port series resistor First resistor A continuously adjustable resistor; the first capacitor Interstage coupling capacitors Cross-coupling capacitors It is a continuously adjustable capacitor.

[0011] Furthermore, based on the required center frequency, relative bandwidth, return loss, transmission zero position, and attenuation adjustment range of the filter attenuator, the lossless filter response is first obtained, and then expressed as an attenuation constant. This represents different target attenuation states. For each target attenuation state, a generalized lossy filter coupling matrix synthesis method is adopted to directly distribute the required attenuation amount to the filter attenuator port section. Under the conditions of satisfying the required filter order, bandwidth, return loss and transmission zero position, the corresponding lossy coupling matrix is ​​obtained.

[0012] Furthermore, the attenuation amount, resonator loss, interstage coupling inductance, and interstage coupling capacitance under different attenuation states can be uniformly determined under the same comprehensive framework; the lossy coupling matrix obtained under different attenuation states is mapped to the actual circuit.

[0013] Furthermore, in practical reconfigurable circuits, PIN diodes can be used to implement a continuously adjustable input port series resistor. Output port series resistor and the first resistor A varactor diode is used to realize a continuously adjustable capacitor, the first capacitor. Interstage coupling capacitors and cross-coupling capacitors .

[0014] Compared with the prior art, the present invention has the following beneficial technical effects:

[0015] 1) Based on the theory of lossy filter synthesis, the attenuation is directly incorporated into the filter synthesis process to achieve an integrated design of filtering and adjustable attenuation functions.

[0016] 2) By coordinating the control of network loss, resonant frequency and coupling parameters, passband flatness, return loss and transmission zero stability are maintained during wide-range attenuation adjustment.

[0017] 3) Continuous attenuation reconstruction can be achieved by adjusting only a few key resistor and capacitor parameters, and it features a compact structure, simple control and easy integration. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the equivalent circuit structure of the reconfigurable filter attenuator of the present invention, which shows the series resistance form after the port loss and external coupling transformation.

[0020] Figure 2 This is a schematic diagram comparing the combined response of the coupling matrix and the simulation results of the equivalent circuit schematic under different target attenuation states of the present invention.

[0021] Figure 3 This is a schematic diagram of the microstrip layout structure according to an embodiment of the present invention.

[0022] Figure 4 This is a schematic diagram of the S-parameter results of layout electromagnetic simulation under different attenuation states in an embodiment of the present invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] This invention proposes a passband flat reconfigurable filter attenuator based on lossy synthesis, such as... Figure 1 As shown, the filter attenuator is a fourth-order filter with a cascaded quadrupole (CQ) structure. This filter employs a symmetrical structure, which can reduce the control input by half. The filter attenuator includes an input port impedance. Output port impedance Input port series resistor Output port series resistor Two first capacitors Two first resistors Two first inductors Two second capacitors Two second inductors Two interstage coupling capacitors Cross-coupling capacitors and interstage coupling inductors .

[0025] Input port impedance One end is grounded, and the other end is connected to the input port series resistor. One end is used as the input terminal; a resistor is connected in series at the input port. The other end is connected to a cross-coupling capacitor. One end, the first interstage coupling capacitor One end of the first adjustable parallel LC resonator; the other end of the first adjustable parallel LC resonator is grounded; the first interstage coupling capacitor. The other end is connected to the interstage coupling inductor. One end of the first lossless parallel LC resonator; the other end of the first lossless parallel LC resonator is grounded; interstage coupling inductor. The other end is connected to the second interstage coupling capacitor. One end of the second lossless parallel LC resonator; the other end of the second lossless parallel LC resonator is grounded; the second interstage coupling capacitor. The other end is connected to a cross-coupling capacitor. The other end, the output port series resistor One end of the first adjustable parallel LC resonator; the other end of the second adjustable parallel LC resonator is grounded; the output port is connected in series with a resistor. The other end is connected to the output port impedance. One end; output port impedance The other end is grounded as the output port.

[0026] Both the first adjustable parallel LC resonator and the second adjustable parallel LC resonator are composed of a first capacitor. First resistor and the first inductor Both the first and second lossless parallel LC resonators are formed by connecting them in parallel, and both are composed of a second capacitor. and the second inductor They are connected in parallel.

[0027] Input port series resistor Output port series resistor First resistor A continuously adjustable resistor; the first capacitor Interstage coupling capacitors Cross-coupling capacitors It is a continuously adjustable capacitor.

[0028] Based on the aforementioned filter attenuator, and according to the required center frequency, relative bandwidth, return loss, transmission null position, and attenuation adjustment range of the filter attenuator, the lossless filter response is first obtained, and then expressed as an attenuation constant. This represents different target attenuation states. The reflection and transmission parameters of the filter attenuator in the lossy state are defined as follows:

[0029]

[0030]

[0031] in, The attenuation constant is and These are the reflection parameters and transmission parameters of the target in a lossy state, respectively. and These are the reflection and transmission parameters of the lossless filter, respectively. Different attenuation constants are set... This allows us to synthesize the lossy coupling matrix and circuit element parameters corresponding to different attenuation states.

[0032] For each target attenuation state, a generalized lossy filter coupling matrix synthesis method is adopted. The required attenuation is directly distributed at the port of the filter attenuator, and the corresponding lossy coupling matrix is ​​obtained under the conditions of satisfying the required filter order, bandwidth, return loss, and transmission zero position. As a result, the attenuation, resonator loss (loss of the first adjustable parallel LC resonator and the second adjustable parallel LC resonator), interstage coupling inductance, and interstage coupling capacitance under different attenuation states can be uniformly determined under the same synthesis framework, instead of being achieved by additional cascading attenuators after the traditional filter.

[0033] To avoid the attenuation unevenness caused by the narrow-band approximation of port coupling when mapping lossy coupling matrices to circuit parameters, this invention employs a circuit transformation method to convert the parallel resistance of the port to the external coupling into a series resistance, thereby eliminating port coupling. Input port impedance With output port impedance Both are 50 Ω, that is The series resistor at the transformed input port and output port series resistor Calculated as follows:

[0034]

[0035] in, The parallel loss resistor at the port before the transformation. and These are the equivalent series resistances of the input and output terminals after the transformation, i.e., the series resistance at the input port and the series resistance at the output port. For symmetrical structures, the parameters at the input and output terminals can use the same values ​​and be adjusted in pairs.

[0036] After further mapping the lossy coupling matrix obtained under different attenuation states to an actual circuit, the variation of each circuit element with attenuation can be compared. In the fourth-order symmetrical CQ filter attenuator used in this invention, the first inductor... Second inductor Interstage coupling inductor Second capacitor The series resistance at the input port remains constant under different attenuation states. Output port series resistor First resistor First capacitor Interstage coupling capacitors and cross-coupling capacitors The attenuation varies. Therefore, by adjusting only a few of the aforementioned parameters, a wide range of attenuation reconstruction can be achieved while keeping the filter topology unchanged.

[0037] In practical reconfigurable circuits, PIN diodes can be used to implement a continuously adjustable input port series resistor. Output port series resistor and the first resistor A varactor diode is used to realize a continuously adjustable capacitor, the first capacitor. Interstage coupling capacitors and cross-coupling capacitors By changing the bias voltage of the PIN diode and varactor diode, the port losses (input port loss and output port loss), resonator losses, resonant frequency, and interstage coupling capacitance can be changed synchronously according to the parameter relationship obtained by lossy synthesis, thereby achieving continuous reconfigurable adjustment of the passband attenuation.

[0038] This invention employs microstrip technology to realize the proposed reconfigurable filter attenuator. Specifically, it adopts a fourth-order symmetrical CQ structure with a target center frequency of 2 GHz, a relative bandwidth of 35%, a reference return loss of 20 dB, and two finite transmission zeros set at 1.5 GHz and 2.65 GHz, respectively. Based on the above specifications, the lossless filter response is first obtained, and then different attenuation constants are set. Then, the lossy coupling matrix corresponding to the decay state of each target is synthesized, and then the lossy coupling matrix is ​​mapped to... Figure 1 The equivalent circuit shown.

[0039] The circuit element values ​​calculated under different target attenuation states are shown in Table 1. It can be seen that... , , and F remains constant under different decay states, while , , , , and The attenuation varies systematically with the target attenuation. Therefore, in a specific circuit, it can be... , , and Fixed, allowing reconfigurable adjustment only for key parameters that change with decay state.

[0040] Table 1. Circuit component values ​​under different target attenuation states.

[0041]

[0042] like Figure 2 As shown, the combined response of the coupling matrix under different attenuation states agrees well with the simulation results of the corresponding equivalent circuit schematic within the passband. As the target attenuation increases, the overall attenuation level in the passband changes according to the combined result, while the passband flatness and out-of-band rejection remain basically stable, and the return loss does not deteriorate significantly. At the same time, the two finite transmission zeros remain near the preset frequency, indicating that the CQ filter topology and its selectivity characteristics can be maintained while changing the loss distribution.

[0043] To verify the feasibility of this invention, the designed circuit is implemented using a microstrip structure. The substrate is a Rogers 4350 substrate with a thickness of 0.508 mm and a copper thickness of 0.035 mm. The resonator adopts a half-wavelength short-circuit structure. A series resistor is used at the input port. Output port series resistor and the first resistor The first capacitor is implemented using a PIN diode equivalent. Interstage coupling capacitors and cross-coupling capacitors Continuous adjustment is achieved using varactor diodes. Both the PIN diode and the varactor diode are controlled by an external DC bias voltage; changing the bias voltage alters their equivalent resistance or capacitance.

[0044] Figure 3 The layout structure of an embodiment of the present invention is given. To reduce the impact of the bias network on the main RF signal path, the DC bias line is introduced through a high-resistance resistor and is kept as far away as possible from the main RF coupling region; the tuning devices in symmetrical positions can be controlled in pairs to make the circuit parameters at the input and output terminals change synchronously.

[0045] Figure 4 Electromagnetic simulation results of the designed reconfigurable filter attenuator are presented. By adjusting the bias states of the PIN diode and varactor diode, the passband attenuation can be continuously varied from approximately 0.9 dB to 17 dB, with a dynamic adjustment range exceeding 16 dB. Under all attenuation conditions, the amplitude-frequency response within the passband maintains high flatness, and the return loss is better than 15 dB.

[0046] As can be seen from the above results, the present invention utilizes lossy filter synthesis to uniformly design different target attenuation states, and maps the synthesized resonator loss, resonant frequency and interstage coupling capacitance to the same reconfigurable circuit, which can maintain the passband flatness, matching performance and out-of-band selectivity of the filter while achieving wide-range continuous attenuation adjustment.

[0047] This invention is not limited to the above-described embodiments. Without departing from the basic principles of this invention, the filter order, filter topology, resonator form, and implementation methods of adjustable resistors and adjustable capacitors can all be adjusted according to actual applications.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A passband flat reconfigurable filter attenuator based on lossy synthesis, characterized in that, The filter attenuator includes the input port impedance. Output port impedance Input port series resistor Output port series resistor Two first capacitors Two first resistors Two first inductors Two second capacitors Two second inductors Two interstage coupling capacitors Cross-coupling capacitors and interstage coupling inductors ; Input port impedance One end is grounded, and the other end is connected to the input port series resistor. One end is used as the input terminal; a resistor is connected in series at the input port. The other end is connected to a cross-coupling capacitor. One end, the first interstage coupling capacitor One end of the first adjustable parallel LC resonator; the other end of the first adjustable parallel LC resonator is grounded; the first interstage coupling capacitor. The other end is connected to the interstage coupling inductor. One end of the first lossless parallel LC resonator; the other end of the first lossless parallel LC resonator is grounded; interstage coupling inductor. The other end is connected to the second interstage coupling capacitor. One end of the second lossless parallel LC resonator; the other end of the second lossless parallel LC resonator is grounded; the second interstage coupling capacitor. The other end is connected to a cross-coupling capacitor. The other end, the output port series resistor One end of the first adjustable parallel LC resonator; the other end of the second adjustable parallel LC resonator is grounded; the output port is connected in series with a resistor. The other end is connected to the output port impedance. One end; output port impedance The other end is grounded as the output port.

2. The passband flat reconfigurable filter attenuator based on lossy synthesis according to claim 1, characterized in that, Both the first adjustable parallel LC resonator and the second adjustable parallel LC resonator are composed of a first capacitor. First resistor and the first inductor Both the first and second lossless parallel LC resonators are formed by connecting them in parallel, and both are composed of a second capacitor. and the second inductor They are connected in parallel.

3. The passband flat reconfigurable filter attenuator based on lossy synthesis according to claim 1, characterized in that, Input port series resistor Output port series resistor First resistor A continuously adjustable resistor; the first capacitor Interstage coupling capacitors Cross-coupling capacitors It is a continuously adjustable capacitor.

4. The passband flat reconfigurable filter attenuator based on lossy synthesis according to claim 1, characterized in that, Based on the required center frequency, relative bandwidth, return loss, transmission zero position, and attenuation adjustment range of the filter attenuator, the lossless filter response is first obtained, and then expressed as an attenuation constant. This represents different target attenuation states. For each target attenuation state, a generalized lossy filter coupling matrix synthesis method is adopted to directly distribute the required attenuation amount to the filter attenuator port section. Under the conditions of satisfying the required filter order, bandwidth, return loss and transmission zero position, the corresponding lossy coupling matrix is ​​obtained.

5. The passband flat reconfigurable filter attenuator based on lossy synthesis according to claim 4, characterized in that, The attenuation, resonator loss, interstage coupling inductance, and interstage coupling capacitance under different attenuation states can be uniformly determined under the same comprehensive framework; the lossy coupling matrix obtained under different attenuation states is mapped to the actual circuit.

6. The passband flat reconfigurable filter attenuator based on lossy synthesis according to claim 1, characterized in that, In practical reconfigurable circuits, PIN diodes can be used to implement a continuously adjustable input port series resistor. Output port series resistor and the first resistor A varactor diode is used to realize a continuously adjustable capacitor, the first capacitor. Interstage coupling capacitors and cross-coupling capacitors .

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