A dual-band directional coupler with filtering function

Abstract

The present invention discloses a dual-band directional coupler with a filtering function. The overall circuit is symmetric left and right. The first to third horizontal transmission lines are respectively connected in series at both ends of one of the microstrip lines of the central coupling line in sequence. The two outer ends of the horizontal transmission line are respectively connected to port one and port two, and both ends of the other microstrip line of the central coupling line are respectively connected to port three and port four. The first to third parallel resonators are respectively connected in parallel at the front ends of the first to third horizontal transmission lines. By utilizing the dual-mode resonance of the parallel resonators, the control of the coupling coefficient by the horizontal transmission line, and the control of the dual-band coupling degree, isolation degree, and coupling fluctuation by the central coupling line, and combining the linkage adjustment between the structures, the present invention realizes a dual-band directional coupler with a filtering function, that is, it integrates the two functions of dual-band filtering and dual-band directional coupling, and can take into account the coupling degree consistency of the two frequency bands, the in-band coupling fluctuation, and the stop band between the two frequency bands.

Description

Technical Field

[0001] The present invention relates to a microwave communication device, and particularly to a directional coupler. Background Art

[0002] A directional coupler is an indispensable four-port device in the RF front-end. Due to its directional coupling function, it is widely used in scenarios such as power monitoring and signal analysis. With the multi-mode operation or compatibility of wireless communication systems, a directional coupler operating in dual bands has received wide attention, which can be named a dual-band directional coupler and can simultaneously achieve the directional coupling function within two separated frequency bands. Further, a dual-band directional coupler with filtering function can achieve the dual-band frequency selection function on the basis of dual-band directional coupling. Therefore, the dual-band directional coupler with filtering function has good engineering value and application value.

[0003] Currently, there is no report on the dual-band directional coupler with filtering function. Most are dual-band directional couplers without filtering function, and there are mainly three implementation methods: The first one uses a quarter-wavelength sawtooth-shaped coupling line, and series-parallel coupling lines connected by capacitors are respectively introduced on both sides of the coupling line. The problems are that the two directional coupling operating frequency bands do not have frequency selectivity, and the coupling degrees of the two frequency bands differ greatly; the second one is a dual-band directional coupler implemented by a stepped impedance coupling strip line composed of nine-section coupling strip lines symmetrically distributed. The problems are that the two directional coupling operating frequency bands do not have frequency selectivity, and there is no stop band formed between the two operating frequency bands; the third one is implemented by adding quarter-wavelength coupling lines on both sides of a traditional quarter-wavelength directional coupler. The problems are that the two directional coupling operating frequency bands do not have frequency selectivity, and the coupling degree fluctuation within the band is large, resulting in a narrow coupling degree bandwidth.

[0004] In view of the above-mentioned prior art, it is necessary to propose a dual-band directional coupler with filtering function, which can achieve dual-band filtering and dual-band directional coupling functions, and the coupling degrees of the two frequency bands are similar, the coupling fluctuation within the band is small, and there can be a stop band between the two frequency bands. Summary of the Invention

[0005] Object of the Invention: Aiming at the above-mentioned prior art, a dual-band directional coupler with filtering function is proposed to achieve the two functions of dual-band filtering and directional coupling, and at the same time take into account the coupling degree consistency of the two frequency bands, the coupling fluctuation within the band, and the stop band characteristics between the two frequency bands.

[0006] Technical Solution: A dual-band directional coupler with filtering function includes Port 1 to Port 4, a central coupling line, three pairs of horizontal transmission lines, and three pairs of parallel resonators, and the overall circuit is symmetric left and right;

[0007] The center coupling line includes two coupled parallel microstrip lines. The first to third horizontal transmission lines are respectively connected in series at both ends of one of the microstrip lines of the center coupling line. The two outer ends of the horizontal transmission lines are respectively connected to port one and port two, and both ends of the other microstrip line of the center coupling line are respectively connected to port three and port four.

[0008] Each parallel resonator respectively includes two microstrip lines. One end of one microstrip line is open, and one end of the other microstrip line is shorted. The other ends of the two microstrip lines are interconnected through a connection point. The first to third parallel resonators are respectively connected in parallel at the front ends of the first to third horizontal transmission lines.

[0009] Further, the electrical length of the center coupling line is between 0.26 λ g ~ 0.30 λ g where λ g is the guided wavelength corresponding to the center frequency of the low-frequency passband. The even-mode impedance and odd-mode impedance of the center coupling line are respectively between 61 Ω and 65 Ω and between 43 Ω and 47 Ω.

[0010] Further, the electrical lengths of the first to third horizontal transmission lines are all between 0.10λ g ~ 0.12λ g where the corresponding impedances are respectively between 61 Ω and 63 Ω, between 53 Ω and 55 Ω, and between 45 Ω and 47 Ω.

[0011] Further, in the first and third parallel resonators, the electrical lengths of the microstrip lines with one end open are all between 0.14 λ g ~ 0.16 λ g where the corresponding impedances are all between 33 Ω and 35 Ω. The electrical lengths of the microstrip lines with one end shorted are all between 0.13 λ g ~ 0.15 λ g where the corresponding impedances are all between 30 Ω and 32 Ω. In the second parallel resonator, the electrical length of the microstrip line with one end open is between 0.16 λ g ~ 0.18 λ g where the corresponding impedance is between 28 Ω and 30 Ω. The electrical length of the microstrip line with one end shorted is between 0.10λ g ~ 0.12λ g where the corresponding impedance is between 31 Ω and 33 Ω.

[0012] Beneficial effects: Existing dual-band directional couplers do not have frequency selectivity, and some designs also have problems such as large differences in coupling degrees between two frequency bands, large in-band coupling fluctuations, or no stopband between two operating frequency bands. The present invention combines a horizontally transmission line and a parallel resonator connected in sequence with a central coupling line. By utilizing the dual-mode resonance of the parallel resonator, the control of the coupling coefficient by the horizontally transmission line, and the control of the dual-band coupling degree, isolation degree, and coupling fluctuations by the central coupling line, and combining the linkage adjustment between structures, a dual-band directional coupler with a filtering function is achieved, that is, it combines the two functions of dual-band filtering and dual-band directional coupling, and can take into account the coupling degree consistency of two frequency bands, in-band coupling fluctuations, and the stopband between two frequency bands.

[0013] Specifically, the parallel resonator is composed of a transmission line with one end open and the other end short-circuited, and is connected to the transmission channel through an intermediate connection point. Each parallel resonator is a dual-mode resonator, which can form a resonance point in each of the two operating frequency bands. Combining with the horizontally transmission line and the central coupling line can form a dual-band filtering response on the through channel and the coupling channel, and form three isolation zeros in each of the two frequency bands to improve the isolation degree. At the same time, the parallel resonator can adjust the frequency ratio of the two frequency bands, the transmission zeros between the two operating frequency bands, and the stopband width.

[0014] Each horizontally transmission line is connected to the parallel resonator in sequence and is located on both sides of the central coupling line. The electrical length and impedance of each horizontally transmission line can adjust the coupling coefficient between the parallel resonators required for the filtering response of the through channel and the coupling channel, and control the bandwidth, matching, in-band transmission fluctuations, and coupling fluctuations of the dual-band directional coupler.

[0015] The central coupling line is located at the center of the entire circuit, which can control the coupling degree, isolation degree, and coupling fluctuations of the dual-band directional coupler, and at the same time affect the coupling coefficient between the parallel resonators on both sides, the matching of the two frequency bands, and the edge roll-off. Description of the Drawings

[0016] Figure 1 It is the circuit diagram of the dual-band directional coupler with a filtering function;

[0017] Figure 2 It is the matching and transmission simulation response of the dual-band directional coupler with a filtering function in the embodiment;

[0018] Figure 3 It is the coupling and isolation simulation response of the dual-band directional coupler with a filtering function in the embodiment;

[0019] Figure 4 It is the directivity simulation response of the dual-band directional coupler with a filtering function in the embodiment. Detailed Embodiments

[0020] The present invention will be further explained below in conjunction with the accompanying drawings.

[0021] As Figure 1 shown, a dual-band directional coupler with a filtering function includes Port 1 to Port 4, a central coupling line 1, three pairs of horizontal transmission lines 2, 3, 4, and three pairs of parallel resonators 5, 6, 7. The overall circuit is symmetric left and right.

[0022] The central coupling line 1 includes two coupled parallel microstrip lines. The electrical length of the central coupling line 1 is between 0.26 λ g ~0.30 λ g where λ g is the guided wavelength corresponding to the center frequency of the low-frequency passband. The even-mode impedance and odd-mode impedance of the central coupling line 1 are between 61 Ω and 65 Ω and between 43 Ω and 47 Ω respectively.

[0023] The electrical lengths of the three pairs of horizontal transmission lines 2, 3, 4 are all between 0.10λ g ~0.12λ g where their corresponding impedances are between 61Ω and 63 Ω, between 53 Ω and 55 Ω, and between 45 Ω and 47 Ω respectively.

[0024] The parallel resonators 5, 6, 7 each include two microstrip lines. One end of one microstrip line is open, and one end of the other microstrip line is short-circuited to ground. The other ends of the two microstrip lines are interconnected through a connection point. Among them, in parallel resonators 5 and 7, the electrical lengths of the microstrip lines with one end open are both between 0.14 λ g ~0.16 λ g where the corresponding impedances are both between 33 Ω and 35 Ω; the electrical lengths of the microstrip lines with one end short-circuited are both between 0.13 λ g ~0.15 λ g where the corresponding impedances are both between 30 Ω and 32 Ω. In parallel resonator 6, the electrical length of the microstrip line with one end open is between 0.16 λ g ~0.18 λ g where the corresponding impedance is between 28 Ω and 30Ω; the electrical length of the microstrip line with one end short-circuited is between 0.10λ g ~0.12λ g where the corresponding impedance is between 31 Ω and 33 Ω.

[0025] The three pairs of horizontal transmission lines 2, 3, 4 are respectively and sequentially connected in series at both ends of one of the microstrip lines of the central coupling line 1 to form the horizontal transmission line of the directional coupler. The outer ends of this horizontal transmission line, that is, the ends of the two horizontal transmission lines 4, are respectively connected to Port 1 and Port 2, and both ends of the other microstrip line of the central coupling line 1 are respectively connected to Port 3 and Port 4.

[0026] The parallel resonators 5, 6, and 7 are respectively connected in parallel to the front ends of the horizontal transmission lines 2, 3, and 4 close to the center coupling line 1. Specifically, the two parallel resonators 5 are respectively connected to the common point of the center coupling line 1 and the horizontal transmission line 2 through their connection points, the two parallel resonators 6 are respectively connected to the common point of the horizontal transmission line 2 and the horizontal transmission line 3 through their connection points, and the two parallel resonators 7 are respectively connected to the common point of the horizontal transmission line 3 and the horizontal transmission line 4 through their connection points.

[0027] When a signal is input from Port 1, after passing through the alternately distributed horizontal transmission lines and parallel resonators, it converges into the center coupling line. Subsequently, the signal is divided into three paths. One path of the signal passes through the alternately distributed horizontal transmission lines and parallel resonators again and is output from the through port (Port 2), the second path of the signal is output from the coupling port (Port 3), and the third path of the signal is output from the isolation port (Port 4). Under the action of the overall circuit, a dual-band directional coupler with a filtering function is formed.

[0028] In this process, each parallel resonator is a dual-mode resonator and can form a resonance point in each of the two operating frequency bands. When the six parallel resonators are combined with the horizontal transmission lines and the center coupling line, they can help the overall circuit form a fast roll-off response on the through channel and the coupling channel, that is, form a dual-frequency filtering response, and form three isolation zeros in each of the two operating frequency bands of the isolation channel to improve the isolation degree. At the same time, the impedance of the corresponding transmission line of the parallel resonator can adjust the frequency ratio of the two operating frequency bands, and the electrical length and impedance of the microstrip line with one end open in the parallel resonator can adjust the transmission zeros and stopband width between the two operating frequency bands of the through channel and the coupling channel.

[0029] The electrical length and impedance of each horizontal transmission line are mainly used to adjust the coupling coefficient between the parallel resonators required for the filtering responses of the through channel and the coupling channel, and are used to control the bandwidth, matching, in-band transmission fluctuation, and coupling fluctuation of the dual-band directional coupler. The center coupling line can control the coupling degree, isolation degree, and coupling fluctuation of the dual-band directional coupler, and at the same time affect the coupling coefficient between the parallel resonators on both sides of it, the matching of the two frequency bands, and the edge roll-off.

[0030] Compared with the prior art, the present invention realizes two functions of dual-band filtering and dual-band directional coupling, and takes into account the coupling degree consistency of the two frequency bands, in-band coupling fluctuation, and stopband between the two frequency bands and other characteristics. In this embodiment, when Port 1 is used as the input port, the matching and transmission simulation responses are as Figure 2 shown, the coupling and isolation simulation responses are as Figure 3 shown, and the directivity simulation response is as Figure 4 shown. From Figure 2It can be seen that there are two passbands on the through-through path. The center frequency of the low-frequency passband is 1.51 GHz. There are six transmission poles in the passband corresponding to a sixth-order filtering response. The frequency range corresponding to the 3-dB bandwidth is 1.2 - 1.82 GHz, that is, the relative bandwidth is 41.1%. The ratio of the -3dB bandwidth to the -30dB bandwidth is 72.1%. The center frequency of the high-frequency passband is 3.94 GHz. There are six transmission poles in the passband also corresponding to a sixth-order filtering response. The frequency range corresponding to the 3-dB bandwidth is 3.53 - 4.36 GHz, that is, the relative bandwidth is 21%. The ratio of the -3dB bandwidth to the -30dB bandwidth is 70.9%. The stopband frequency range of 20 dB between the two passbands is 1.87 GHz - 3.44 GHz. From Figure 3 It can be seen that the coupling degree of both frequency bands is 15 dB. The relative bandwidth corresponding to the 15 dB ± 2 dB coupling range of the low-frequency passband is 38.4%. The ratio of the -3dB bandwidth to the -30dB bandwidth of its coupling channel is 53.8%. The relative bandwidth corresponding to the 15 dB ± 2 dB coupling range of the high-frequency passband is 21.6%. The ratio of the -3dB bandwidth to the -30dB bandwidth of its coupling channel is 57.8%. The frequency range with isolation greater than 30 dB is 1.34 GHz - 1.77 GHz and 3.62 GHz - 3.91 GHz. From Figure 4 It can be seen that the frequency range with directivity maintained above 14 dB is 1.33 GHz - 1.77 GHz and 3.62 GHz - 4.21 GHz.

[0031] 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 dual-band directional coupler with filtering function, characterized in that: It includes ports 1 to 4, a central coupling line (1), three pairs of horizontal transmission lines and three pairs of parallel resonators, and the overall circuit is symmetrical. The central coupling line (1) comprises two coupled parallel microstrip lines, and the first to third horizontal transmission lines are respectively connected in series at the two ends of one of the microstrip lines of the central coupling line (1); the two outer ends of the horizontal transmission line are respectively connected to port one and port two, and the two ends of the other microstrip line of the central coupling line (1) are respectively connected to port three and port four; Each parallel resonator comprises two microstrip lines, one end of one microstrip line is open-circuited, one end of the other microstrip line is short-circuited, and the other ends of the two microstrip lines are interconnected through a connection point; the first to third parallel resonators are respectively connected in parallel to the front ends of the first to third horizontal transmission lines, and the front ends are the horizontal transmission lines close to the central coupling line (1); The electrical length of the center coupling line (1) is 0.26 λ g ~0.30 λ g Between g is the wavelength of the waveguide corresponding to the center frequency of the low-frequency passband; the electrical lengths of the first to third horizontal transmission lines are all 0.10λ g ~0.12λ g In the first and third parallel resonators, the electrical length of the open-ended microstrip line is 0.14 λ. g ~0.16 λ g The electrical length of the short-circuited microstrip line is between 0.13 λ g ~0.15 λ g In the second parallel resonator, the electrical length of the open-ended microstrip line is 0.16 λ. g ~0.18 λ g The electrical length of the short-circuited microstrip line is between 0.10λ g ~0.12λ g between.

2. The dual-band directional coupler with filtering function according to claim 1, characterized in that: The even-mode impedance and odd-mode impedance of the center coupled line (1) are between 61 Ω and 65 Ω and between 43 Ω and 47 Ω, respectively.

3. The dual-band directional coupler with filtering function according to claim 1 or 2, characterized in that: The corresponding impedances of the first to third horizontal transmission lines are between 61 Ω and 63 Ω, between 53 Ω and 55 Ω, and between 45 Ω and 47 Ω, respectively.

4. The dual-band directional coupler with filtering function according to claim 3, characterized in that: The corresponding impedances of the first and third parallel resonators are both between 33 Ω and 35 Ω, and the corresponding impedances of the microstrip line with one end short-circuited are both between 30 Ω and 32 Ω; the corresponding impedance of the second parallel resonator is between 28 Ω and 30 Ω, and the corresponding impedance of the microstrip line with one end short-circuited is between 31 Ω and 33 Ω.

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