Wide stopband filtering coupler based on rectangular coaxiality

Abstract

The invention relates to the technical field of wireless communication, in particular to a wide-stop-band filtering coupler based on a rectangular coaxial structure, which comprises a rectangular coaxial outer conductor upper cavity, an inner conductor circuit and a rectangular coaxial outer conductor lower cavity, and is characterized in that the inner conductor circuit is arranged between the rectangular coaxial outer conductor upper cavity and the rectangular coaxial outer conductor lower cavity through a medium supporting block; the inner conductor circuit comprises an input port, a straight-through port, a coupling port, an isolation port and a branch line coupler structure. Four ports of the branch line coupler structure are respectively in coupling connection with the input port, the straight-through port, the coupling port and the isolation port through a quarter-wavelength open-circuit parallel coupling line structure. The novel rectangular coaxial transmission line is adopted for design, so that the circuit has the advantages of the rectangular coaxial metal transmission line, the electromagnetic shielding structure enables the circuit not to be easily interfered by external electromagnetic wave signals, and the rectangular coaxial transmission line can control the impedance requirement by changing the proportion of the inner conductor and the outer conductor according to different design requirements.

Description

Technical Field

[0001] The present invention relates to the field of wireless communication technologies, and particularly to a wide-stopband filter coupler based on rectangular coaxial. Background Art

[0002] As a core passive device in microwave radio frequency circuits, the traditional branch-line directional coupler occupies an important position in microwave radio frequency communication systems due to its high structural symmetry, excellent port isolation, and easy planar integration. Its typical four-port network consists of four quarter-wavelength transmission lines forming an orthogonal loop, which can achieve 3dB power distribution and 90° phase difference output at the center frequency, so it is widely used in microwave circuits such as balanced amplifiers, mixers, and array antenna feeding networks. However, the traditional branch-line directional coupler has a defect that its high-order harmonic suppression ability and anti-spurious interference ability are poor. In a communication system, it can disrupt adjacent wireless communication systems, generate noise, thereby affecting the communication quality. In severe cases, information can be lost, resulting in the paralysis of communication equipment. Therefore, it is necessary to suppress the generation of harmonics.

[0003] In microwave radio frequency circuits, filters and branch-line couplers are usually cascaded to suppress harmonics and eliminate noise on the basis of achieving 3dB power distribution and 90° phase difference output. However, this method often brings large insertion losses and design sizes because the losses follow the superposition effect of each device, and the additional cascaded cables and potential cascaded mismatches will further deteriorate the overall performance, increasing the losses. In modern microwave radio frequency circuits, the characteristics of losses, sizes, weights, etc. of each part will directly or indirectly affect the performance of the entire circuit and system. Summary of the Invention

[0004] In order to introduce transmission zeros outside the band to broaden the stopband range without changing the passband characteristics and achieve the purpose of wide-stopband design, the present invention proposes a wide-stopband filter coupler based on rectangular coaxial, which includes an upper cavity of the rectangular coaxial outer conductor, an inner conductor circuit, and a lower cavity of the rectangular coaxial outer conductor. The inner conductor circuit is arranged between the upper cavity of the rectangular coaxial outer conductor and the lower cavity of the rectangular coaxial outer conductor through a dielectric support block. The inner conductor circuit includes an input port, a through port, a coupling port, an isolation port, and a branch-line coupler structure. The four ports of the branch-line coupler structure are respectively coupled to the input port, the through port, the coupling port, and the isolation port through a quarter-wavelength open-circuit parallel-coupling line structure.

[0005] Furthermore, dumbbell-shaped DGS structures are formed by etching at the central positions where the upper cavity of the rectangular coaxial outer conductor and the lower cavity of the rectangular coaxial outer conductor are coupled to the input port, the through port, the coupling port, and the isolation port through the parallel-coupling line structure.

[0006] Furthermore, the upper cavity of the rectangular coaxial outer conductor, the inner conductor circuit, and the lower cavity of the rectangular coaxial outer conductor are made of copper material.

[0007] Furthermore, the dielectric support block is made of insulating Teflon material.

[0008] Furthermore, the transmission line of the branch-line coupler structure adopts a stub-loaded transmission line.

[0009] Furthermore, air is filled as the dielectric between the upper cavity of the rectangular coaxial outer conductor, the lower cavity of the rectangular coaxial outer conductor and the inner conductor circuit.

[0010] Furthermore, by adjusting the dimensions of the parallel-coupled line structure and the distances between the parallel-coupled line structure and the input port, through-port, coupled port, and isolated port, the odd- and even-mode impedances of the parallel-coupled line are controlled.

[0011] Compared with the prior art, the present invention has the following beneficial effects:

[0012] 1. The present invention uses a novel transmission line, the rectangular coaxial transmission line, for design, enabling the overall circuit design to have the advantages of a rectangular coaxial metal transmission line, including its unique electromagnetic shielding structure that makes it less susceptible to external electromagnetic wave signals. The rectangular coaxial transmission line can control impedance requirements by changing the ratio of the inner and outer conductors according to different design requirements, with strong design flexibility. At the same time, since the dielectric material filled between the inner and outer conductors of the rectangular coaxial transmission line is air, it has a higher power capacity and lower dielectric radiation loss.

[0013] 2. By adding a rectangular coaxial dumbbell-shaped DGS structure, new transmission zeros are generated outside the band without changing the passband transmission characteristics, effectively suppressing the interference of out-of-band signals and further increasing the stopband rejection range. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is an exploded schematic diagram of a wide-stopband filter-coupler based on rectangular coaxial of the present invention;

[0015] Figure 2 is a schematic diagram of the inner conductor circuit of a wide-stopband filter-coupler based on rectangular coaxial of the present invention;

[0016] Figure 3 is a planar schematic diagram of a wide-stopband filter-coupler based on rectangular coaxial of the present invention;

[0017] Figure 4 is a 3D schematic diagram of a wide-stopband filter-coupler based on rectangular coaxial of the present invention;

[0018] Figure 5This is a schematic diagram of the performance of a wide stopband filter coupler based on rectangular coaxial in the present invention. Among them, Fig. (a) is the schematic diagram of the S-parameter |S 11 | / |S 21 | effect diagram, and Fig. (b) is the schematic diagram of the S-parameter |S 31 | / |S 41 | effect diagram, and Fig. (c) is the port phase difference;

[0019] Among them, 1. Upper cavity of the rectangular coaxial outer conductor; 2. Inner conductor circuit; 3. Dielectric support block; 4. Lower cavity of the rectangular coaxial outer conductor; 5. Input port; 6. Through port; 7. Coupling port; 8. Isolation port; 9. Branch line coupler structure; 10. Parallel coupled line structure; 11. Dumbbell-shaped DGS structure. Specific embodiments

[0020] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0021] The present invention proposes a wide stopband filter coupler based on rectangular coaxial, including an upper cavity of the rectangular coaxial outer conductor, an inner conductor circuit, and a lower cavity of the rectangular coaxial outer conductor. The inner conductor circuit is arranged between the upper cavity of the rectangular coaxial outer conductor and the lower cavity of the rectangular coaxial outer conductor through a dielectric support block. The inner conductor circuit includes an input port, a through port, a coupling port, an isolation port, and a branch line coupler structure. The four ports of the branch line coupler structure are respectively coupled and connected to the input port, the through port, the coupling port, and the isolation port through a quarter-wavelength open parallel coupled line structure.

[0022] This embodiment gives a specific implementation manner of a wide stopband filter coupler based on rectangular coaxial, and its structural explosion diagram is as Figure 1 shown. From top to bottom, they are successively the upper cavity 1 of the rectangular coaxial outer conductor, the inner conductor circuit 2, the dielectric support block 3, and the lower cavity 4 of the rectangular coaxial outer conductor; Figure 2Schematic diagram of the inner conductor circuit, where the inner conductor circuit 2 includes an input port 5, a through port 6, a coupling port 7, an isolation port 8, and a branch-line coupler structure 9. The central position structure in the inner conductor circuit 2 is a miniaturized branch-line coupler structure 9 formed by using a stub-loaded transmission line instead of a quarter-wavelength transmission line. By adjusting the length of the loaded stub, it has the same transmission response as a traditional branch-line coupler and generates a transmission zero TZ1 in the out-of-band region, suppressing out-of-band signals while effectively reducing the circuit size of the traditional branch-line coupler. A parallel-coupled line structure 10 is added between the branch-line coupler structure 9 and the input port 5, the through port 6, the coupling port 7, and the isolation port 8. By adjusting the size of the parallel-coupled line and the distance between the two transmission lines, the odd and even mode impedances of the parallel-coupled line can be controlled. Finally, two transmission zeros TZ2 and TZ3 can be generated on both sides of the passband, effectively increasing the filtering characteristics of the circuit, forming a steep sideband roll-off rate, and improving the suppression effect of the stopband.

[0023] Figure 3 Planar schematic diagram of a wide-stopband filtering coupler based on rectangular coaxial in the present invention. Figure 4 3D schematic diagram of a wide-stopband filtering coupler based on rectangular coaxial in the present invention, which includes a dumbbell-shaped DGS structure 11. In this embodiment, a dumbbell-shaped DGS structure in the shape of rectangular coaxial is adopted. The overall inner conductor circuit 2 is placed in the upper cavity 1 of the rectangular coaxial outer conductor and the lower cavity 4 of the rectangular coaxial outer conductor through a dielectric support block 3. The dielectric support block 3 uses insulating Teflon material, and the upper cavity 1 of the rectangular coaxial outer conductor, the lower cavity 4 of the rectangular coaxial outer conductor, and the inner conductor circuit 2 use copper material.

[0024] In this embodiment, two dielectric support blocks 3 are provided for the coupling connection between the parallel-coupled line structure and the input port, the through port, the coupling port, and the isolation port. The two dielectric support blocks are respectively arranged on both sides of the coupling connection, used to support the coupling connection between the parallel-coupled line structure and the corresponding port. The branch-line coupler structure in this embodiment is supported by four dielectric support blocks, and each dielectric support block is arranged below the stub-loaded transmission line.

[0025] The upper cavity 1 of the rectangular coaxial outer conductor and the lower cavity 4 of the rectangular coaxial outer conductor together form the rectangular coaxial outer conductor cavity, and the medium filled inside is air. An operation of etching the dumbbell-shaped DGS structure 11 is performed on the corresponding outer conductor cavity part at the center of the inner conductor parallel-coupled line structure 10. The dumbbell-shaped DGS structure makes the outer conductor cavity etch through up and down at the corresponding position to form an etched structure similar to a dumbbell shape.

[0026] The prior art proposed that the author Nie Wei designed a filtering branch-line coupler with second-harmonic suppression in the paper "Research on Microwave and Millimeter-Wave Integrated Passive Circuits". The present invention is an improvement based on the coupler in this research. It is designed based on a rectangular coaxial transmission line. By changing the original DGS structure on the basis of the original circuit structure, after adding a dumbbell-shaped DGS to the circuit, compared with the situation without adding the dumbbell-shaped DGS, the current on both sides of the feeder in the grounding metal plate will have a longer flow path, which can be equivalently regarded as a series of additional inductors. Changing the etched area of its grounding layer can force the current to detour a longer path, thereby affecting the series inductance value. And the charge accumulation in the center slot line area of the dumbbell-shaped DGS is equivalent to a parallel capacitor, and this equivalent capacitor is affected by the width of the center slot line. Therefore, by adjusting the geometric dimensions of the DGS (such as the width of the slot line or the etched area), the equivalent inductance and capacitance values can be accurately adjusted, and then the transmission characteristics of the transmission line can be changed, so that it can form attenuation poles or optimize the harmonic suppression ability in a specific frequency band.

[0027] The performance simulation of the present invention is as Figure 5 , and the results show that the center frequency is 2.4 GHz. In the range of 1.93 GHz to 2.61 GHz, the input return loss (|S 11 |) is better than 20 dB, the isolation of the isolation port (|S 41 |) is also better than 20 dB, and the insertion loss (|S 21 | / |S 31 |) is better than 0.2 dB. The port phase difference between the through port and the coupled port is 90° ± 0.55°. A total of four transmission zeros are generated outside the passband. Among them, TZ1 is the transmission zero generated by the stub-loaded transmission line, TZ2 and TZ3 are the transmission zeros generated by the loaded coupled lines, and TZ4 is the transmission zero generated by adding the DGS structure of the rectangular coaxial transmission line. These four transmission zeros enable the lower stopband of the coupler to have a very wide signal suppression range. In the frequency range of 3.43 GHz to 12.07 GHz, the signal suppression is better than 20 dB, and the stopband width is 3.6f0. Comparing with the filtering branch-line coupler with second-harmonic suppression in the paper "Research on Microwave and Millimeter-Wave Integrated Passive Circuits", the design in the paper uses a microstrip line structure, and the design results show that it has a stopband suppression range of 1.4f0, while the present invention uses a rectangular coaxial transmission line and introduces zeros using a dumbbell-shaped DGS structure, making it have a stopband suppression range of 3.6f0.

[0028] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by the terms "coaxial", "bottom", "one end", "top", "middle", "the other end", "upper", "one side", "top", "inner", "outer", "front", "center", "both ends", etc. are based on the orientation or positional relationships shown in the drawings. These are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention.

[0029] In the present invention, unless otherwise clearly specified and defined, the terms "mount", "set", "connect", "fix", "rotate", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements or the interaction relationship between two elements. Unless otherwise clearly defined, for those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0030] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A wide stopband filter coupler based on rectangular coaxial, comprising a rectangular coaxial outer conductor upper cavity, an inner conductor circuit, and a rectangular coaxial outer conductor lower cavity, wherein the inner conductor circuit is arranged between the rectangular coaxial outer conductor upper cavity and the rectangular coaxial outer conductor lower cavity through a dielectric support block, characterized in that: The inner conductor circuit includes an input port, a through port, a coupled port, an isolated port, and a branch line coupler structure. The four ports of the branch line coupler structure are coupled and connected with the input port, the through port, the coupled port, and the isolated port through a quarter-wavelength open parallel coupled line structure.

2. The wide stopband filter coupler based on rectangular coaxial according to claim 1, characterized in that: A dumbbell-shaped DGS structure is formed by etching an upper cavity of a rectangular coaxial outer conductor and a lower cavity of a rectangular coaxial outer conductor at a center position where a parallel coupling line structure is coupled with an input port, a through port, a coupling port, and an isolation port.

3. The wide stopband filter coupler based on rectangular coaxial according to claim 1, characterized in that: The rectangular coaxial outer conductor upper cavity, the inner conductor circuit and the rectangular coaxial outer conductor lower cavity are made of copper material.

4. The wide stopband filter coupler based on rectangular coaxial according to claim 1, characterized in that: The dielectric support block is made of insulating Teflon material.

5. The wide stopband filter coupler based on rectangular coaxial according to claim 1, characterized in that: The transmission line of the branch line coupler structure adopts a branch-loaded transmission line.

6. The wide stopband filter coupler based on rectangular coaxial according to claim 1, characterized in that: Air is filled as a medium between the rectangular coaxial outer conductor upper cavity, the rectangular coaxial outer conductor lower cavity and the inner conductor circuit.

7. The wide stopband filter coupler based on rectangular coaxial according to claim 1, characterized in that: The even-odd mode impedance of the parallel coupled line is controlled by adjusting the size of the parallel coupled line structure and the spacing between the parallel coupled line structure and the input port, the through port, the coupled port and the isolated port.

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