A Lumped Element Filtering Directional Coupler

Abstract

The invention discloses a lumped element filtering directional coupler, in which a central LC mutual coupling circuit is cascaded with two side LC mutual coupling circuits, four E-type LC circuits are connected to the outside, and the side LC mutual coupling circuits and the E-type LC circuits are used to adjust the transmission poles and the transmission zeros of each channel, the central LC mutual coupling circuit adjusts the coupling, and the overall circuit controls the impedance matching and the directivity and expands the stopband bandwidth, thereby realizing a lumped element filtering directional coupler, which has the advantages of high integration, small size and wide stopband, and can take into account the characteristics of broadband operation and high frequency selectivity.

Description

Technical Field

[0001] The invention relates to a microwave communication device, in particular to a lumped element filtering directional coupler. Background Art

[0002] Directional coupler is an important RF front-end device, which can couple the signal of the through channel to the coupled channel output at a certain ratio, and the signal of the isolation channel is much smaller than that of the coupled channel. It is often used in application scenarios such as signal detection and signal analysis. The device that incorporates the filtering function in the directional coupler is usually called a filtering directional coupler. It can realize multiple functions such as frequency selection, suppression of out-of-band interference signals and directional coupling with a single device, which is conducive to reducing the circuit size, improving integration and reducing system losses at the system level. Furthermore, the lumped element filtering directional coupler realized by lumped elements is smaller in size and easier to integrate than the traditional filtering directional coupler realized by distributed parameter transmission lines. Therefore, the lumped element filtering directional coupler has good engineering value and application value.

[0003] Most of the existing filter directional couplers are distributed parameter filter directional couplers, and there are two ways to implement them: the first is to use the center coupling line as the basis, combined with cascaded transmission lines and parallel branches to realize the filter directional coupler. Due to the addition of too many branches and the cascade of multiple groups of transmission lines, this method has a large overall size and a narrow stopband. The second method is to realize the functions of filtering and directional coupling through a multi-layer cross-type three-line coupling line structure with wide-side coupling. Compared with the first method, the size is reduced, but the design method based on distributed parameter transmission lines limits the degree of size reduction. The multi-layer design method increases the complexity of the structure, and this method also has problems such as narrow stopband, narrow filtering bandwidth and low frequency selectivity. At present, there is no report on the design of lumped element filter directional couplers. Therefore, it is necessary to propose a lumped element filter directional coupler that has a wide stopband characteristic while maintaining high integration and functional integration, and can take into account broadband and high frequency selectivity. Summary of the invention

[0004] Purpose of the invention: In view of the above-mentioned prior art, a lumped element filtering directional coupler is proposed to improve the integration, reduce the size and structural complexity, widen the stopband bandwidth, and take into account both broadband operation and high frequency selectivity.

[0005] Technical solution: A lumped element filtering directional coupler, the overall structure is centrally symmetrical, including: ports one to four, a central LC mutual coupling circuit, two side LC mutual coupling circuits, and four E-type LC circuits; a side LC mutual coupling circuit is cascaded on the left and right sides of the central LC mutual coupling circuit, each side LC mutual coupling circuit is connected to two E-type LC circuits on the outside, and the connection between the side LC mutual coupling circuit and the E-type LC circuit is connected to ports one to four respectively.

[0006] Furthermore, the side LC mutual coupling circuit is used to generate two transmission poles and one transmission zero in the through channel, generate a coupling zero in the coupling channel, and generate three isolation zeros in the passband in the isolation channel; the E-type LC circuit is used to generate two transmission poles and two transmission zeros in the through channel, and generate two coupling zeros in the coupling channel.

[0007] Furthermore, in the through channel, the through response has five transmission poles and three transmission zeros; wherein, the middle transmission pole is provided by the central LC mutual coupling circuit, the two adjacent transmission poles are provided by the side LC mutual coupling circuit, and the two outermost transmission poles are provided by the E-type LC circuit; the transmission zero at zero frequency is provided by the side LC mutual coupling circuit, and the two transmission zeros near the passband are provided by the E-type LC circuit; in the coupled channel, the coupled response has three coupling zeros; wherein, the coupling zero at zero frequency is provided by the side LC mutual coupling circuit, and the two coupling zeros near the passband are provided by the E-type LC circuit.

[0008] Furthermore, the central LC mutual coupling circuit is composed of a coupling inductor and six capacitors; wherein, four grounding capacitors are connected in parallel to four ends of the coupling inductor, and the other two capacitors are respectively connected across the left and right sides of the coupling inductor.

[0009] Furthermore, each side LC mutual coupling circuit is composed of two coupled inductors and eight capacitors, and forms two symmetrical groups of structures; in each group of structures, two grounded capacitors are respectively connected in parallel to a pair of diagonal ends of the coupled inductor, and the other pair of diagonal ends of the coupled inductor are respectively connected to one of the ports of the device and one end of the coupled inductor in the central LC mutual coupling circuit, and the other two capacitors are respectively connected across the left and right sides of the coupled inductor.

[0010] Furthermore, each E-type LC circuit consists of two inductors and three capacitors; the two inductors are connected in series, and one end of the series structure is connected to one of the ports of the device; the three grounding capacitors are respectively connected in parallel at both ends of the series structure and at the common point of the two inductors.

[0011] Beneficial effects: Most existing filtering directional couplers are distributed parameter designs, with large size, complex structure, low integration and narrow stopband. Some designs also have problems such as narrow working bandwidth and low frequency selectivity. The present invention cascades the central LC mutual coupling circuit with two side LC mutual coupling circuits, and four E-type LC circuits are connected to the outside. The side LC mutual coupling circuit and the E-type LC circuit are used to adjust the transmission poles and the transmission zeros of each channel, the central LC mutual coupling circuit adjusts the coupling, and the overall circuit controls the impedance matching and directivity and expands the stopband bandwidth, thereby realizing a lumped element filtering directional coupler, which has the advantages of high integration, small size and wide stopband, and can take into account the characteristics of broadband operation and high frequency selectivity.

[0012] Specifically, the central LC mutual coupling circuit is composed of a coupled inductor and six capacitors, located at the center of the entire circuit structure, which can affect the impedance matching, coupling, and directionality of the overall circuit, and is the basis for the overall circuit to achieve direct-through, coupling, and isolation.

[0013] The side LC mutual coupling circuit is composed of two coupled inductors and eight capacitors, located on both sides of the central LC mutual coupling circuit, and is used to generate two transmission poles and one transmission zero in the through channel to provide the through channel broadband and good frequency selectivity, generate a coupling zero in the coupling channel to improve the coupling channel frequency selectivity, and generate three isolation zeros in the passband in the isolation channel to improve the isolation bandwidth; at the same time, the series inductor and the parallel grounding capacitor formed with the central LC mutual coupling circuit have a low-pass effect, which can expand the stopband bandwidth of each channel.

[0014] The E-type LC circuit consists of two inductors and three capacitors, is located at the outermost side of the circuit, and is connected to the adjacent LC mutual coupling circuit. It is used to generate two transmission poles and two transmission zeros in the through channel to improve the bandwidth and frequency selectivity of the through channel, and to generate two coupling zeros in the coupling channel to further improve the frequency selectivity of the coupling channel. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a circuit diagram of a lumped element filtering directional coupler of the present invention;

[0016] Figure 2 The matching, transmission and coupling simulation responses of the lumped element filtering directional coupler of the present invention;

[0017] Figure 3 The isolation and directivity simulation response of the lumped element filtering directional coupler of the present invention;

[0018] Figure 4 The simulated response of the phase difference between the through and coupled outputs of the lumped element filtering directional coupler of the present invention. DETAILED DESCRIPTION

[0019] The present invention will be further explained below in conjunction with the accompanying drawings.

[0020] like Figure 1 As shown, a lumped element filtering directional coupler includes ports 1 to 4, a central LC mutual coupling circuit 1, side LC mutual coupling circuits 2 and 3, and E-type LC circuits 4 to 7. The side LC mutual coupling circuits 2 and 3 are cascaded on the left and right sides of the central LC mutual coupling circuit 1, and the outer side of each side LC mutual coupling circuit is connected to two E-type LC circuits, and the connection between the side LC mutual coupling circuit and the E-type LC circuit is connected to ports 1 to 4 respectively.

[0021] The central LC mutual coupling circuit 1 is composed of a coupling inductor 101 and capacitors 102 - 107 ; four grounding capacitors 102 - 105 are connected in parallel to four terminals of the coupling inductor 101 , and capacitors 106 and 107 are connected across the left and right sides of the coupling inductor 101 , respectively.

[0022] The side LC mutual coupling circuit 2 is composed of coupling inductors 201, 202 and capacitors 203-210; wherein grounding capacitors 203 and 204 are respectively connected in parallel to a pair of diagonal ends of the coupling inductor 201, and the other pair of diagonal ends of the coupling inductor 201 are respectively connected to port one and the first end of the coupling inductor 101 in the center LC mutual coupling circuit 1; grounding capacitors 205 and 206 are respectively connected in parallel to a pair of diagonal ends of the coupling inductor 202, and the other pair of diagonal ends of the coupling inductor 202 are respectively connected to port three and the third end of the coupling inductor 101 in the center LC mutual coupling circuit 1, and capacitors 204 and 206 are commonly grounded; capacitors 207 and 208 are respectively connected across the left and right sides of the coupling inductor 201, and capacitors 209 and 210 are respectively connected across the left and right sides of the coupling inductor 202.

[0023] The side LC mutual coupling circuit 3 is composed of coupling inductors 301, 302 and capacitors 303-310; wherein grounding capacitors 303 and 304 are respectively connected in parallel to a pair of diagonal ends of the coupling inductor 301, and the other pair of diagonal ends of the coupling inductor 301 are respectively connected to port 2 and the second end of the coupling inductor 101 in the center LC mutual coupling circuit 1; grounding capacitors 305 and 306 are respectively connected in parallel to a pair of diagonal ends of the coupling inductor 302, and the other pair of diagonal ends of the coupling inductor 302 are respectively connected to port 4 and the fourth end of the coupling inductor 101 in the center LC mutual coupling circuit 1, and capacitors 304 and 306 are commonly grounded; capacitors 307 and 308 are respectively connected across the left and right sides of the coupling inductor 301, and capacitors 309 and 310 are respectively connected across the left and right sides of the coupling inductor 302.

[0024] The E-type LC circuit 4 is composed of inductors 401, 402 and capacitors 403~405; wherein the inductor 401 and the inductor 402 are connected in series, and one end of the series structure is connected to port 1; the grounding capacitor 403, the grounding capacitor 405, and the grounding capacitor 404 are respectively connected in parallel at both ends of the series inductors 401 and 402 and at the common point of the series inductors.

[0025] The E-type LC circuit 5 is composed of inductors 501, 502 and capacitors 503~505; wherein the inductor 501 and the inductor 502 are connected in series, and one end of the series structure is connected to port 2; the grounding capacitor 503, the grounding capacitor 505, and the grounding capacitor 504 are respectively connected in parallel at both ends of the series inductors 501 and 502 and at the common point of the series inductors.

[0026] The E-type LC circuit 6 is composed of inductors 601, 602 and capacitors 603~605; wherein the inductor 601 and the inductor 602 are connected in series, and one end of the series structure is connected to port three; the grounding capacitor 603, the grounding capacitor 605, and the grounding capacitor 604 are respectively connected in parallel at both ends of the series inductors 601 and 602 and at the common point of the series inductors.

[0027] The E-type LC circuit 7 is composed of inductors 701, 702 and capacitors 703~705; wherein the inductor 701 and the inductor 702 are connected in series, and one end of the series structure is connected to port four; the grounding capacitor 703, the grounding capacitor 705, and the grounding capacitor 704 are respectively connected in parallel at both ends of the series inductors 701 and 702 and at the common point of the series inductors.

[0028] The overall structure of the present invention is centrally symmetrical, and the performance obtained by the signal input from any port is exactly the same. When the signal is input from port one, it is fed into the central LC mutual coupling circuit 1 after passing through the E-type LC circuit 4 and the side LC mutual coupling circuit 2, and then the signal is divided into three paths, and is output from port two to port four respectively after passing through the side LC mutual coupling circuits 2, 3 and the E-type LC circuits 5, 6, and 7, and a lumped element filtering directional coupler is formed under the action of the overall circuit.

[0029] In this process, the through channel is from port one to port two, and the through response has five transmission poles and three transmission zeros: the middle transmission pole is provided by the central LC mutual coupling circuit, the two adjacent transmission poles are provided by the side LC mutual coupling circuit, and the two outermost transmission poles are provided by the E-type LC circuit; the transmission zero at zero frequency is provided by the side LC mutual coupling circuit, and the two transmission zeros near the passband are provided by the E-type LC circuit. The five transmission poles and three transmission zeros provide broadband operation and high frequency selective filtering functions for the through response.

[0030] The coupling channel is from port one to port three. For the coupling response, the coupling zero point at zero frequency is provided by the side LC mutual coupling circuit, and the two coupling zero points near the passband are provided by the E-type LC circuit. The three coupling zero points improve the frequency selectivity of the coupling channel and ensure the filtering function of the coupling channel. The isolation channel is from port one to port four. For the isolation response, the three isolation zero points in the passband are all provided by the side LC mutual coupling circuit to improve the isolation bandwidth. The coupling degree of the overall circuit is mainly controlled by the central LC mutual coupling circuit; the impedance matching and directivity of the overall circuit are controlled by the overall circuit. In addition, the series inductance and parallel grounding capacitor of the through channel, coupling channel and isolation channel have a low-pass effect, which can expand the stopband bandwidth of each channel.

[0031] In summary, the lumped element filtering directional coupler combines the capabilities of filtering and directional coupling, and has a wide stop band, which can take into account both broadband operation and high frequency selectivity. At the same time, since the present invention adopts a design method of full lumped parameter elements, it has high integration and small size.

[0032] In this embodiment, when port 1 is used as an input port, the matching, transmission and coupling responses are as follows: Figure 2 As shown, the isolation and directional response are as follows Figure 3 As shown, the phase difference response between the through end and the coupled end is as follows Figure 4 As shown. Figure 2 It can be seen that the center frequency is 0.84 GHz, the frequency range of the 3-dB working bandwidth of the through channel is 0.44-1.23 GHz, that is, the relative bandwidth can reach 94.6%, the -10-dB matching bandwidth can reach 92.2%, the insertion loss at the center frequency is 0.15 dB, and the 20-dB out-of-band suppression frequency range of the through channel can reach 4.17 f 0, the through channel realizes five transmission poles (0.46 GHz, 0.54 GHz, 0.86 GHz, 1.09 GHz, 1.21 GHz) and three transmission zeros (0GHz, 0.34 GHz, 1.33 GHz); the three transmission zeros greatly improve the frequency selectivity of the through channel, and the ratio of -3dB bandwidth to -30dB bandwidth can reach 86.8%; the coupling degree of the coupling channel is 16dB, and the relative bandwidth corresponding to the 16dB±2dB coupling range can reach 88.1%, and the 20-dB out-of-band suppression frequency range of the coupling channel can reach 4.17 f 0, the coupling channel also achieves three coupling zero points (0GHz, 0.33 GHz, 1.33 GHz), which also improves the frequency selectivity of the coupling channel. The ratio of -3dB bandwidth to -30dB bandwidth can reach 95.3%. Figure 3It can be seen that the isolation within the matching frequency band is greater than 28dB, the isolation channel has three isolation zero points, which improves the isolation bandwidth; the directivity within the matching frequency band remains above 11dB. Figure 4 It can be seen that the phase difference between the output signals of the through end and the coupled end is 90°, and the relative bandwidth of the ±2° phase difference fluctuation can reach 75%.

[0033] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A lumped element filtering directional coupler, It is characterized in that The overall structure is centrally symmetrical, including: ports 1 to 4, a central LC mutual coupling circuit, two side LC mutual coupling circuits, and four E-type LC circuits; a side LC mutual coupling circuit is cascaded on the left and right sides of the central LC mutual coupling circuit, and the outer side of each side LC mutual coupling circuit is connected to two E-type LC circuits, and the connection between the side LC mutual coupling circuit and the E-type LC circuit is connected to ports 1 to 4 respectively; The central LC mutual coupling circuit is composed of a coupling inductor and six capacitors; among them, four capacitors are grounded capacitors connected in parallel to the four ends of the coupling inductor, and the other two capacitors are connected across the left and right sides of the coupling inductor respectively; Each side LC mutual coupling circuit is composed of two coupled inductors and eight capacitors, and forms two symmetrical groups of structures; in each group of structures, two grounded capacitors are respectively connected in parallel to a pair of diagonal ends of the coupled inductors, and the other pair of diagonal ends of the coupled inductors are respectively connected to one port of the lumped element filtering directional coupler and one end of the coupled inductors in the central LC mutual coupling circuit, and the other two capacitors are respectively connected across the left and right sides of the coupled inductors in each group of structures; Each E-type LC circuit consists of two inductors and three capacitors; the two inductors are connected in series, and one end of the series structure is connected to one port of the lumped element filtering directional coupler; the three grounded capacitors are respectively connected in parallel at both ends of the series structure and at the common point of the two inductors.

2. The lumped element filtering directional coupler according to claim 1, It is characterized in that The side LC mutual coupling circuit is used to generate two transmission poles and one transmission zero in the through channel, generate a coupling zero in the coupling channel, and generate three isolation zeros in the passband in the isolation channel; the E-type LC circuit is used to generate two transmission poles and two transmission zeros in the through channel, and generate two coupling zeros in the coupling channel.

3. The lumped element filtering directional coupler according to claim 2, It is characterized in that In the through channel, the through response has five transmission poles and three transmission zeros; among them, the middle transmission pole is provided by the central LC mutual coupling circuit, the two adjacent transmission poles are provided by the side LC mutual coupling circuit, and the two outermost transmission poles are provided by the E-type LC circuit; the transmission zero at zero frequency is provided by the side LC mutual coupling circuit, and the two transmission zeros near the passband are provided by the E-type LC circuit; in the coupled channel, the coupled response has three coupling zeros; among them, the coupling zero at zero frequency is provided by the side LC mutual coupling circuit, and the two coupling zeros near the passband are provided by the E-type LC circuit.

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