Microstrip filtering branch line coupler

Abstract

The invention belongs to the field of radio frequency microwave passive devices, discloses a microstrip filtering branch line coupler, and aims to provide a compact microwave passive device capable of simultaneously realizing coupling and filtering functions so as to meet the requirements of a modern communication system on miniaturization, high selectivity and out-of-band rejection capability. According to the technical scheme, each part comprises an input port, an output port, a coupling port, an isolation port, four uniform impedance half-wavelength resonators, two uniform impedance half-wavelength resonators of which the centers are loaded with stub lines, four 50-omega microstrip line ports and four high-impedance transmission lines connected with the resonators. According to the invention, a resonant circuit is introduced at a quarter-wavelength transmission line node of the multi-branch broadband branch line coupler, which is equivalent to a coupling topology network. Four half-wavelength resonators with uniform impedance and two half-wavelength resonators with center loading stub lines are utilized to realize a coupling function of the branch line coupler, and a filtering characteristic is introduced to the coupler. The resonators are connected with the ports through high-impedance transmission lines, and the resonators are mutually coupled through gaps. According to the filtering branch line coupler disclosed by the invention, the coupling bandwidth can be increased, and the high-order filtering characteristic is introduced to improve the filtering selection characteristic.

Description

Technical Field

[0001] The present invention relates to the technical field of radio frequency microwave passive devices, and more specifically, to a microstrip filtering branch line coupler. Background Art

[0002] With the rapid development of wireless communication technology, modern communication systems are developing in the direction of high frequency, large bandwidth, miniaturization and multifunctionality. Especially in the fields of 5G communication, satellite communication, Internet of Things and radar systems, the performance requirements for RF and microwave equipment are constantly increasing. In order to meet the needs of these complex systems, microwave passive devices (such as couplers, filters, power dividers, etc.) face huge challenges in achieving signal processing accuracy, reducing insertion loss, improving isolation and miniaturization. Branch line couplers have become a common device for multi-port coupling and power distribution due to their easy design, simple structure and wide applicable frequency range. However, with the increase in device selectivity and size requirements, branch line couplers have gradually exposed some limitations.

[0003] In the design of branch line couplers, it is usually impossible to directly suppress out-of-band interference signals, and it is difficult to achieve out-of-band suppression while maintaining good impedance matching. For modern communication equipment, out-of-band stray signals and adjacent channel interference will significantly affect system performance, reduce communication quality, and increase the complexity of signal processing. Therefore, integrating filtering functions in couplers can effectively suppress out-of-band interference, so that the coupler can effectively filter out unnecessary clutter signals while transmitting the main frequency signal, thereby improving the signal-to-noise ratio of the communication link.

[0004] As an important microwave component, the filter branch line coupler is widely used in modern wireless communication systems, especially in key tasks such as signal distribution, spectrum shaping, and modulation and demodulation. Its main function is to distribute the input signal to multiple output ports at a set power ratio, and to ensure the phase difference between the output ports, while ensuring good isolation between the input port and the isolation port. This coupler not only needs to have low insertion loss and high isolation, but also needs to achieve excellent filtering characteristics within a specific frequency band to optimize the overall performance of the system.

[0005] For the research on filter branch line couplers, the current design method is mainly to design by cascading filter structures at the input and output ports of the coupler or using a coupling topology network. However, in the process of designing filter branch line couplers, it was found that the cascade filter structure method would lead to relatively large insertion loss and structure size, while the coupling topology network method had a relatively narrow bandwidth and the filter selectivity could be further improved. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a microstrip filtering branch line coupler, which adopts the method of introducing a resonant circuit into a multi-branch broadband branch line coupler structure, aiming to provide a compact microwave passive device that can simultaneously realize coupling and filtering functions, so as to meet the requirements of modern communication systems for miniaturization, high selectivity and out-of-band suppression capability.

[0007] The embodiment of the present invention is implemented by the following technical solutions:

[0008] An embodiment of the present invention provides a microstrip filter branch line coupler, comprising: an input port, an output port, a coupling port, an isolation port, a half-wavelength uniform impedance resonator, a half-wavelength uniform impedance resonator loaded with a short stub in the middle, and a high-impedance transmission line portion. Among them, the implementation of the present invention is implemented using six resonators, and the six resonators are coupled to each other through gaps. Since the two middle resonances need to be coupled with three resonators respectively, a half-wavelength uniform impedance resonator loaded with a short stub in the center is used to implement it. The four resonators on the edge only need to be coupled with two resonators, and a half-wavelength uniform impedance resonator can be used for design. The input port, output port, coupling port and isolation port are all connected by a microstrip line with an impedance of 50 ohms, and each port is connected to a half-wavelength uniform impedance resonator through a high-impedance transmission line.

[0009] The beneficial effects of the present invention are as follows: the present invention introduces a resonant circuit based on the multi-branch broadband branch line coupler structure, and equates it to a new coupling topology network. A resonant circuit is introduced at the quarter transmission line node of the multi-branch broadband branch line coupler, and its node is equivalent to a resonator, and the quarter-wavelength transmission line is equivalent to a converter. Since the design is based on the multi-branch broadband branch line coupler structure, its coupling bandwidth can be increased compared to the classical branch line coupler structure. In addition, the transmission line nodes of the multi-branch broadband branch line coupler can be equivalent to multiple resonators, so a high-order filtering response can be achieved from the input port to the output port to further improve the filtering selectivity. In the embodiments of the present invention, only a three-branch broadband branch line coupler is demonstrated, but it is not limited to the design of a three-branch coupler. Based on the design method of the present invention, it can be extended to the design of couplers with more branches. With the increase of branches, the coupling bandwidth of the branch line coupler will also increase. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the technical solution of the present invention, the accompanying drawings are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention. In the accompanying drawings: Figure 1 A coupling topology network of a microstrip filter branch line coupler of the present invention; Figure 2It is a schematic diagram of the hierarchical structure of the microstrip filtering branch line coupler of the present invention; Figure 3 The circuit layout and dimension parameter diagram of the microstrip filter branch line coupler of the present invention; Figure 4 It is an S parameter simulation curve diagram of the microstrip filter branch line coupler of the present invention. DETAILED DESCRIPTION

[0011] Certain terms used throughout this specification and claims refer to some specific components. For example, the book uses terms such as "first", "second", "upper left", and "lower right" to distinguish different elements, but these elements are not limited to these terms, which are only used to distinguish different elements.

[0012] The specific implementation of the present invention will be described in more detail below with reference to the accompanying drawings.

[0013] Figure 1 This is the coupling topology network of the microstrip filter branch line coupler in the implementation process of the present invention. This topology network is proposed based on the structure of the three-branch branch line coupler, and an LC resonant circuit is introduced at the node where the quarter-wavelength transmission line of the three-branch coupler intersects. Then its structure can be equivalent to Figure 1 In the coupling topology network shown in the figure, the introduced LC resonant circuit can be equivalent to a resonator, and the original quarter-wavelength transmission line can be equivalent to a K transformer. Further, we can get Figure 1 The coupled topology network of the 1000A is shown in Figure 1, where the six gray circles represent the resonator nodes, and the solid lines between the resonators represent the electrical coupling, and the coupling coefficient is represented by Kij. The external quality factor between the four ports and the resonator is represented by Q.

[0014] based on Figure 1 The coupling topology network of the microstrip filter branch line coupler of the present invention is mainly composed of an input port, an output port, a coupling port, an isolation port, four half-wavelength uniform impedance resonators, two half-wavelength uniform impedance resonators with center-loaded short stubs, and a high-impedance transmission line.

[0015] Specifically, four half-wavelength uniform impedance resonators with the same structure are used to replace Figure 1 Resonators 1, 3, 4 and 6 in the coupled topology network; two half-wavelength uniform impedance resonators with the same structure and center-loaded short stubs are used to replace resonators 2 and 5 in the coupled topology network.

[0016] The coupling coefficients k12, k23, k45, and k56 in the coupled topology network have the same size, and are all used to characterize the coupling strength between the four half-wavelength uniform impedance resonators at the edge and the two half-wavelength uniform impedance resonators with center-loaded short stubs. Their sizes can be controlled by reasonably adjusting the coupling gap g1 between the half-wavelength uniform impedance resonator and the half-wavelength uniform impedance resonator with center-loaded short stubs.

[0017] The coupling coefficients k16 and k34 in the coupled topology network have the same size, and both are used to characterize the coupling strength between the four half-wavelength uniform impedance resonators at the edge. The size can be controlled by reasonably adjusting the coupling gap g2 between the half-wavelength uniform impedance resonators.

[0018] The coupling coefficient k25 in the coupled topology network is used to characterize the coupling strength between the half-wavelength uniform impedance resonators of the two center-loaded short stubs at the edge, and its size can be controlled by reasonably adjusting the coupling gap g3 between the half-wavelength uniform impedance resonators of the center-loaded short stubs.

[0019] Since the branch line coupler is symmetrical, the four external ports and the resonator have the same external quality factor, which is represented by Q. In the embodiment of the present invention, the 50-ohm transmission line of the external port is connected to the resonator by a high-impedance transmission line, and the size of the external quality factor Q can be controlled by adjusting the electrical length and impedance of the high-impedance transmission line, and adjusting the position of the high-impedance transmission line feeding on the half-wavelength uniform impedance resonator.

[0020] Based on the above analysis, the hierarchical structure diagram of the embodiment of the microstrip filtering branch line coupler of the present invention is as follows: Figure 2 The circuit part includes input port microstrip line 1, output port microstrip line 2, coupling port microstrip line 3, isolation port microstrip line 4, left upper half-wavelength uniform impedance resonator microstrip line 5, right upper half-wavelength uniform impedance resonator microstrip line 6, right lower half-wavelength uniform impedance resonator microstrip line 7, left lower half-wavelength uniform impedance resonator microstrip line 8, center upper center-loaded short stub half-wavelength uniform impedance resonator microstrip line 9, center lower center-loaded short stub half-wavelength uniform impedance resonator microstrip line 10, output port microstrip line 11, output port microstrip line 12, output port microstrip line 13, output port microstrip line 14, output port microstrip line 15, output port microstrip line 16, output port microstrip line 17, output port microstrip line 18, output port microstrip line 19, output port microstrip line 20, output port microstrip line 21, output port microstrip line 22, output port microstrip line 23, output port microstrip line 24, output port microstrip line 25, output port microstrip line 26, output port microstrip line 27, output port microstrip line 28, output port microstrip line 29, output port microstrip line 30, output port microstrip line 31, output port microstrip line 32, output port microstrip line 33, output port microstrip line 34, output port microstrip line 35, output port microstrip line 36, output port microstrip line 37, output port microstrip line 38, output port microstrip line 39, output port microstrip line 40, output port microstrip line 41 The input port 1 is connected to a high-impedance microstrip transmission line 11 of a half-wavelength uniform impedance resonator 5 on the upper left side, the output port 2 is connected to a high-impedance microstrip transmission line 12 of a half-wavelength uniform impedance resonator 6 on the upper right side, the coupling port 3 is connected to a high-impedance microstrip transmission line 13 of a half-wavelength uniform impedance resonator 7 on the lower right side, the isolation port 4 is connected to a high-impedance microstrip transmission line 14 of a half-wavelength uniform impedance resonator 8 on the lower left side, an upper circuit plane 15 composed of all microstrip lines, a central dielectric layer 16 and a bottom ground plane 17.

[0021] The characteristic impedances of the input port microstrip line 1, the output port microstrip line 2, the coupling port microstrip line 3, and the isolation port microstrip line 4 are all 50 ohms.

[0022] The input port microstrip line 1, the upper left half-wavelength uniform impedance resonator microstrip line 5 and the high impedance microstrip transmission line 11 are directly connected, the output port microstrip line 2, the upper right half-wavelength uniform impedance resonator microstrip line 6 and the high impedance microstrip transmission line 12 are directly connected, the coupling port microstrip line 3, the lower right half-wavelength uniform impedance resonator microstrip line 7 and the high impedance microstrip transmission line 13 are directly connected, and the isolation port microstrip line 4, the lower left half-wavelength uniform impedance resonator microstrip line 8 and the high impedance microstrip transmission line 14 are directly connected.

[0023] In order to facilitate the mutual coupling between the resonators, the half-wavelength uniform impedance resonator 5 on the upper left side, the half-wavelength uniform impedance resonator 6 on the upper right side, the half-wavelength uniform impedance resonator 7 on the lower right side, the half-wavelength uniform impedance resonator 8 on the lower left side, the half-wavelength uniform impedance resonator 9 with a center-loaded short stub on the upper center side, and the half-wavelength uniform impedance resonator 10 with a center-loaded short stub on the lower center side are all bent, and all bends are achieved by vertical bending.

[0024] The upper circuit plane 15 composed of all microstrip lines is designed by etching. The middle dielectric layer 16 is a high-frequency dielectric substrate with a relative dielectric constant of 3.5. The bottom ground plane 17 is implemented by a full-plane copper coating method. Figure 1 and Figure 2 The circuit layout and size parameters of the microstrip filter branch line coupler of the present invention are as follows: Figure 3 shown.

[0025] Figure 4 This is an S parameter simulation curve diagram provided for the microstrip filter branch line coupler embodiment of the present invention, wherein port 1 in the curve diagram corresponds to input port 1 in the present invention, port 2 corresponds to output port 2 in the present invention, port 3 corresponds to coupling port 3 in the present invention, and port 4 corresponds to isolation port 4 in the present invention.

[0026] See also Figure 4 The center frequency of the microstrip filter branch line coupler embodiment of the present invention is 2.9GHz, the in-band return loss is better than 20dB, the in-band insertion loss is 3.6dB, and the in-band isolation is also better than 20dB. The embodiment provides good coupling and isolation. Through the above structure and implementation method, the present invention provides a microstrip filter branch line coupler with high selectivity and low insertion loss, which can be widely used in wireless communications, radar, Internet of Things and other fields that require high-performance filter couplers.

[0027] The above descriptions are merely embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, several modifications and improvements may be made without departing from the principles of the present invention. For example, designs based on multi-branch broadband branch line couplers such as four-branch and five-branch branch line couplers should also be considered to be within the scope of protection of the present invention.

Claims

1. A microstrip filter branch line coupler, characterized in that: include: An input port (1), an output port (2), a coupling port (3), an isolation port (4), a half-wavelength uniform impedance resonator (5) (6) (7) (8), a half-wavelength uniform impedance resonator with a center-loaded stub (9) (10), and a high impedance transmission line (11) (12) (13) (14), wherein the input port (1) is connected to the resonator (5) through the high impedance transmission line (11), the output port (2) is connected to the resonator (6) through the high impedance transmission line (12), the coupling port (3) is connected to the resonator (7) through the high impedance transmission line (13), and the isolation port (4) is connected to the resonator (8) through the high impedance transmission line (14). In addition, all the above-mentioned elements (1)-(14) are implemented on the upper circuit plane (15), and also include a central dielectric layer (16) and a bottom ground plane (17).

2. The microstrip filter branch line coupler according to claim 1, characterized in that: The filtering branch line coupler implementation scheme is implemented by introducing a resonant circuit at a quarter-wavelength transmission line node of a multi-branch broadband branch line coupler structure and using a resonator after it is equivalent to a coupling topology network. The four edge resonators need to be able to couple in two directions and be connected to the external port feed, and the middle resonator needs to be able to couple in three directions.

3. The microstrip filter branch line coupler according to claim 1, characterized in that: The two identical half-wavelength uniform impedance resonators (9) and (10) with center-loaded stubs are placed in the center of the coupler. The ends of the stubs loaded in the center of the resonator are connected in parallel, and the two ends of the half-wavelength uniform impedance resonator are folded, so that coupling can be achieved in three directions.

4. The microstrip filter branch line coupler according to claim 1, characterized in that: The four half-wavelength uniform impedance resonators (5), (6), (7), and (8) have the same geometric structure and electrical length and are located at four positions above and below the two sides of the half-wavelength uniform impedance resonator (9) and (10) with a centrally loaded stub. The four half-wavelength uniform impedance resonators are folded and bent to further reduce the volume while achieving coupling at both ends of the resonator.

5. The microstrip filter branch line coupler according to claim 1, characterized in that: The four half-wavelength uniform impedance resonators (5), (6), (7), (8) and the two half-wavelength uniform impedance resonators (9), (10) with center-loaded stubs are directly coupled to each other through gaps.

6. The microstrip filter branch line coupler according to claim 1, characterized in that: The four half-wavelength uniform impedance resonators (5), (6), (7), (8) and the four external ports (1), (2), (3), (4) are connected via high impedance transmission lines (11), (12), (13), (14), and the impedance value and length are adjusted to optimize the connection so as to ensure good impedance matching and reduce insertion loss.

7. The microstrip filter branch line coupler according to claim 1, characterized in that: The input port (1), the output port (2), the coupling port (3), and the isolation port (4) are connected using a microstrip line with an impedance of 50Ω.

8. The microstrip filter branch line coupler according to claim 1, characterized in that: The upper circuit plane (15) including (1)-(14) is printed on the upper surface of a high-frequency dielectric substrate (16) with a relative dielectric constant of 3.5 by etching. The bottom ground plane (17) is a surface completely covered with copper.

9. The microstrip filter branch line coupler according to claim 1, characterized in that: The introduction of a resonant circuit based on the multi-branch broadband branch line coupler structure can increase its coupling bandwidth compared to the classic branch line coupler structure. The transmission line nodes of the multi-branch broadband branch line coupler are equivalent to multiple resonators, and a high-order filtering response can be achieved from the input port to the output port to improve the filtering selectivity.

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