A directional coupler with reconfigurable filtering characteristics of a multiplexed resonant stub

Abstract

This invention discloses a directional coupler with reconfigurable filtering characteristics that reuses resonant stubs, belonging to the field of microwave and millimeter-wave circuit technology. The coupler includes a main body consisting of a main transmission line, a coupling transmission line, and four ports. A serpentine resonant stub unit is connected in series on both the main and coupling transmission lines. Each resonant stub leads out an equivalent inductance stub and is connected to a reflective single-pole double-throw switch. The other end of each switch is connected to a variable capacitor. This invention allows the variable capacitor to be selectively connected to either the main or coupling resonant stub via switching, achieving time-division multiplexing of the resonant stubs and forming an adjustable parallel LC resonant circuit, resulting in two operating modes: when the capacitor is connected to the main path, both the main and coupling channels simultaneously possess low-pass filtering characteristics with continuously adjustable cutoff frequencies; when the capacitor is connected to the coupling channel, only the coupling channel is filtered, while the main channel achieves low insertion loss pass-through across the entire frequency band. This invention has the advantages of compact size, low insertion loss, and a wide filtering tuning range.

Description

Technical Field

[0001] This invention belongs to the field of microwave and millimeter-wave circuits, and specifically relates to a directional coupler with reconfigurable filtering characteristics that reuses resonant stubs. Background Technology

[0002] Directional couplers, as core passive devices in RF and microwave communication systems, satellite communication, radar detection, and RF test equipment, primarily perform signal power distribution, coupling sampling, impedance matching, and clutter suppression. They are key components in the miniaturization, integration, and multi-functionality of modern RF front-ends. With the rapid development of reconfigurable communication systems, integrated devices combining coupling and filtering characteristics have become a research hotspot. Existing reconfigurable filtering directional couplers are typically implemented by cascading filters and couplers, loading independent resonant units, or using switch arrays. However, this approach suffers from structural redundancy, large circuit area, high insertion loss, and high design complexity.

[0003] Current technologies generally employ a separate design of directional couplers and reconfigurable filters, meaning the resonant unit is dedicated to filter design, and designs with structural reuse are rarely reported. Furthermore, the filter's variation range is mostly limited to fixed frequency band switching, restricting its application in complex scenarios. Existing designs cannot coordinately control coupling and filtering characteristics, resulting in drawbacks such as narrow tunable range, single filtering mode, and low integration, failing to meet the dual requirements of compact devices and high performance in multi-band, multi-mode communication systems. Figure 1 This is a schematic diagram of a traditional directional coupler topology, whose single coupling branch cannot achieve filtering characteristics for both the coupling channel and the main channel. The paper "Design of Compact Filtering 180-Degree Hybrids With Arbitrary Power Division and Filtering Response" demonstrates that the filter waveform and coupling degree can be adjusted by changing the coupling coefficient between couplers. However, this coupling coefficient can only be controlled by adjusting the gap size during manufacturing, and cannot be extended to achieve reconfigurable capabilities.

[0004] Currently, electronic systems have increasingly higher requirements for the high integration and miniaturization of devices, which has led to the emergence of various functional integration devices. However, traditional directional couplers are difficult to integrate with filters. In addition, in actual links, it is not always necessary to filter the main signal transmission path of the directional coupler. The integrated filtering directional couplers reported in the present paper all filter both the main transmission path and the coupled signal transmission path, which limits the application scenarios. Summary of the Invention

[0005] To address the shortcomings of existing reconfigurable filter directional couplers, such as structural redundancy, large size, high loss, and limited tuning range, this invention proposes a directional coupler with reconfigurable filtering characteristics that reuses resonant stubs. This invention achieves time-division multiplexing of the resonant stubs through switching, combined with a variable capacitor.

[0006] An adjustable LC resonant circuit can be constructed, which can flexibly switch between two working modes: full filtering of the main path and filtering of the coupling path only. The filter cutoff frequency can be continuously adjusted. While achieving independent and controllable frequency response of the main and coupling channels, it also takes into account miniaturization, low insertion loss and high isolation. It can meet the needs of multi-band highly integrated RF front-end systems and has important engineering application value.

[0007] The technical solution adopted in this invention is as follows:

[0008] A directional coupler with reconfigurable filtering characteristics that reuses resonant stubs includes a four-port coupler body consisting of a main transmission line, a coupled transmission line, and corresponding input ports, through ports, coupled ports, and isolation ports.

[0009] The main transmission line is connected in series with a main path serpentine resonant stub unit near the input port, and the coupling transmission line is connected in series with a coupling path serpentine resonant stub unit near the coupling port.

[0010] Both the main path serpentine resonant stub unit and the coupling path serpentine resonant stub unit are multi-segment serpentine broken line structures. Inductor stubs are vertically led out from each broken line segment parallel to the corresponding transmission line. Each inductor stub is respectively connected to reflective single-pole double-throw switch 1, reflective single-pole double-throw switch 2, and reflective single-pole double-throw switch 3.

[0011] The other ends of the three reflective single-pole double-throw switches 1, 2, and 3 are all connected to adjustable capacitors. These three sets of reflective single-pole double-throw switches are used to selectively connect the adjustable capacitor to either the main circuit serpentine resonant stub unit or the coupled circuit serpentine resonant stub unit. This allows the main circuit serpentine resonant stub unit and the coupled circuit serpentine resonant stub unit to be time-division multiplexed and form a parallel LC resonant circuit with the adjustable capacitor, enabling switching between two different low-pass filter operating modes. Simultaneously, by adjusting the capacitance value of the adjustable capacitor, the cutoff frequency of the low-pass filter can be continuously changed, achieving reconfigurable filter characteristics.

[0012] Preferably, the main path serpentine resonant stub unit and the coupled path serpentine resonant stub unit are formed by continuous bending of the same width of the trace, and the number of bending units is set to 3 to 5.

[0013] Preferably, all inductor stubs have the same width; the length of the inductor stubs decreases sequentially along the signal transmission direction.

[0014] Preferably, the capacitance value of the variable capacitor is typically in the range of 0.2pF to 2pF, determined by the required cutoff frequency range of the low-pass filter circuit.

[0015] Preferably, when the reflective single-pole double-throw switch 1, reflective single-pole double-throw switch 2, and reflective single-pole double-throw switch 3 operate together, there are two operating states. The first operating state is when the variable capacitor is connected to the main transmission line; in this state, both the main channel and the coupling channel have low-pass filtering responses. The second operating state is when the variable capacitor is connected to the coupling transmission line; in this state, only the coupling channel has filtering characteristics, and the main channel achieves low insertion loss pass-through across the entire frequency band. The beneficial effects of this invention are as follows:

[0016] This invention utilizes a single-pole double-throw (SPDT) switch to control resonant stubs for connection to either the main transmission line or the coupled transmission line. When the resonant stub is connected to the main transmission line, it enables filtering for both the main and coupled transmission lines. When connected to the coupled transmission line, only the coupled transmission line retains its filtering function. This multiplexing of the resonant stub allows for a compact design. The resonant stub itself integrates an adjustable capacitor, forming a low-pass filter with an adjustable passband cutoff frequency when connected to either the main or coupled transmission line.

[0017] Compared to existing technologies, this invention utilizes a switch to achieve time-division multiplexing of resonant stubs, eliminating the need for two independent resonant filter units and significantly reducing circuit area; it relies on a variable capacitor to achieve continuously adjustable filter cutoff frequency, broadening the device's operating tuning range; it can switch between dual-path synchronous filtering and coupled-path-only filtering modes as needed, adapting to more RF link application scenarios; the overall circuit has lower insertion loss and excellent port isolation performance, making it widely applicable to microwave and millimeter-wave multi-band reconfigurable RF front-end systems, and possessing significant engineering application value. Attached Figure Description

[0018] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the specific embodiments 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 from these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of a traditional directional coupler topology;

[0020] Figure 2 This is a schematic diagram of the directional coupler structure for the reconfigurable filtering characteristics of the multiplexed resonant stub of the present invention;

[0021] Figure 3 The frequency response curve of a traditional directional coupler;

[0022] Figure 4The response curves of the directional coupler with reconfigurable filtering characteristics in the main path and coupling path of this invention are shown.

[0023] Figure 5 The image shows the response curve of the directional coupler with reconfigurable filtering characteristics of the coupled-only pathband according to the present invention.

[0024] Explanation of reference numerals in the attached diagram: 1. Main transmission line, 101. Main resonant stub, 102. First main inductor stub, 103. Second inductor stub, 104. Third inductor stub; 2. Coupled transmission line, 201. Main resonant stub, 202. First inductor stub, 203. Second inductor stub, 204. Third inductor stub; 301. First switch, 302. Second switch, 303. Third switch; 401. First variable capacitor, 402. Second variable capacitor, 403. Third variable capacitor. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] like Figure 2 As shown, this embodiment provides a 6-18GHz directional coupler with reconfigurable filtering characteristics. The directional coupler with reconfigurable characteristics is a four-port network, including an input port, a through port, a coupling port, and an isolation port. The four ports are connected to each other through a main transmission line and a coupling transmission line, and a main path resonant stub is introduced in series on the main transmission line near the input port, and a coupling path resonant stub is introduced on the coupling transmission line near the coupling port.

[0027] Both the main resonant stub and the coupling path resonant stub are multi-segment 90-degree bend serpentine broken line structures. Inductor stubs are vertically led out from the broken line segments parallel to the corresponding transmission lines. Each inductor stub is connected to a reflective single-pole double-throw switch 1, a reflective single-pole double-throw switch 2, and a reflective single-pole double-throw switch 3, respectively.

[0028] The common terminal of three reflective single-pole double-throw switches is connected to a variable capacitor element; the three reflective single-pole double-throw switches control the variable capacitor element to connect to the main resonant stub or the coupling resonant stub, thereby connecting it with the variable capacitor element to form a parallel LC resonant circuit, ultimately forming a low-pass filter topology; by adjusting the capacitance value of the variable capacitor in the low-pass filter, the cutoff frequency adjustment function of the low-pass filter can be realized.

[0029] The length of the transmission line is related to the dielectric constant and thickness of the substrate. In this embodiment, the substrate consists of two layers, with a thickness of 0.254 mm and a dielectric constant of 9.9. The transmission line is located between the upper and lower substrates and is in the form of a stripline. The coupling line is 6 mm long. The main resonant stub and the coupling resonant stub are equivalent to an inductor in a serpentine manner, thus forming an equivalent LC filter circuit with the adjustable capacitor. The main resonant stubs, arranged from left to right, are equivalent to inductances of 1.05, 0.95, and 0.42 nH, respectively, and the parallel stubs, arranged from bottom to top, are equivalent to inductances of 0.62, 0.44, and 0.17 nH, respectively.

[0030] The capacitance value of the variable capacitor element varies from 0.2 to 0.35 pF. According to the cutoff frequency response formula of the low-pass filter, as the capacitance value C of the variable capacitor increases, its cutoff frequency decreases, and vice versa. By changing the capacitance value of the variable capacitor, the filtering response characteristics of the coupled or direct-pass branch can be finally achieved.

[0031] The reflective single-pole double-throw switch has two operating states. In the first state, the three switches control the varactor element connected to the main circuit resonant stub. In this state, both the through port and the coupling port have low-pass filter responses. For comparison, Figure 3 This is the response curve of the directional coupler under ideal conditions without any filtering structure. In this embodiment, when a resonant stub is introduced and the single-pole double-throw switch is connected to the main transmission path, the response curves of both the main signal and the coupled signal will be affected simultaneously. Through simulation, the following can be obtained: Figure 4 The two main paths and the coupling path shown all have filtering characteristic curves, and the cutoff frequency of the low-pass filter can change synchronously with the change of the variable capacitor, thus realizing the adjustable function of the filtering characteristics.

[0032] The second operating state involves three switch-controlled varactor elements connected to the resonant stub of the coupling circuit. In this state, only the coupling port exhibits a low-pass filter response. The frequency response obtained from the coupler simulation in this case is as follows: Figure 5 As shown, filtering characteristics are only present in the curve corresponding to the coupling port, and this filtering response is also adjustable. Furthermore, for the main path, it exhibits low insertion loss through-pass capability across the entire frequency band.

[0033] As can be seen, the directional coupler with reconfigurable filtering characteristics that uses multiple resonant stubs provided by the present invention realizes flexible frequency response control of the main channel and coupling channel of the coupler, solves the problems of fixed frequency band and limited adjustment performance of existing couplers, and at the same time takes into account compact size, low insertion loss and high isolation, meeting the application requirements of related systems.

Claims

1. A directional coupler with reconfigurable filtering characteristics that reuses resonant stubs, comprising a four-port coupler body consisting of a main transmission line, a coupled transmission line, and correspondingly provided input ports, through ports, coupled ports, and isolation ports; Its features are, The main transmission line is connected in series with a main path serpentine resonant stub unit near the input port, and the coupling transmission line is connected in series with a coupling path serpentine resonant stub unit near the coupling port. Both the main path serpentine resonant stub unit and the coupling path serpentine resonant stub unit are multi-segment serpentine broken line structures. Inductor stubs are vertically led out from each broken line segment parallel to the corresponding transmission line. Each inductor stub is respectively connected to reflective single-pole double-throw switch 1, reflective single-pole double-throw switch 2, and reflective single-pole double-throw switch 3. The common terminals of the three reflective single-pole double-throw switches 1, 2, and 3 are all connected to adjustable capacitors. These three sets of reflective single-pole double-throw switches are used to selectively connect the adjustable capacitor to either the main serpentine resonant stub unit or the coupled serpentine resonant stub unit. This allows the main serpentine resonant stub unit and the coupled serpentine resonant stub unit to be time-division multiplexed and form a parallel LC resonant circuit with the adjustable capacitor, enabling switching between two different low-pass filter operating modes. Simultaneously, by adjusting the capacitance value of the adjustable capacitor, the cutoff frequency of the low-pass filter can be continuously changed, achieving reconfigurable filter characteristics.

2. A directional coupler with reconfigurable filtering characteristics that reuses resonant stubs as described in claim 1, characterized in that, The serpentine zigzag structure is formed by continuous 90-degree bends of metal traces of uniform width, with the number of bend units set to 3 to 5.

3. A directional coupler with reconfigurable filtering characteristics that reuses resonant stubs as described in claim 2, characterized in that, All inductor stubs have the same width; the length of the inductor stubs decreases sequentially along the signal transmission direction.

4. A directional coupler with reconfigurable filtering characteristics that reuses resonant stubs as described in claim 3, characterized in that, The capacitance value of the variable capacitor varies from 0.2pF to 2pF, which is determined by the range of the cutoff frequency required by the low-pass filter circuit.

5. A directional coupler with reconfigurable filtering characteristics that reuses resonant stubs as described in claim 4, characterized in that, When the reflective single-pole double-throw switch 1, reflective single-pole double-throw switch 2, and reflective single-pole double-throw switch 3 are used together, there are two working states: The first working state is that the variable capacitor is connected to the main transmission line, and at this time, both the main channel and the coupling channel have low-pass filter responses; the second working state is that the variable capacitor is connected to the coupling transmission line, and at this time, only the coupling channel has filtering characteristics, and the main channel achieves low insertion loss pass-through across the entire frequency band.

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