Gradient coupling type high-selectivity waveguide filter

Abstract

The invention discloses a gradient coupling type high-selectivity waveguide filter, and belongs to the technical field of filters. According to the invention, through a mode of transition from the double-gradient waveguide to the double-gradient resonant coupling structure, broadband and harmonic suppression are realized at the same time, the out-of-band suppression performance of the high-frequency end of the waveguide filter is improved, and a wider stop band is obtained, so that ideal out-of-band suppression performance is realized with fewer orders, and the longitudinal size of the filter is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of filters, and particularly relates to a high-selectivity waveguide filter with a tapered coupling structure. Background Art

[0002] A filter is an important component in the front end of a radio frequency system, which has the function of spectrum selection, that is, passing useful signals, suppressing harmonic and interference signals, and is an indispensable component in the design of microwave and millimeter-wave circuits. The performance of the filter largely determines the overall performance of the radio frequency circuit system and is an essential part of modern communication systems. In recent years, with the rapid development of microwave and millimeter-wave communication technologies, signal crosstalk has become more obvious, posing higher and higher requirements for the performance of filters. Filters in the high-frequency band are mainly designed using waveguide transmission elements. Compared with microstrip filters, waveguide filters have advantages such as high Q value, low loss, large power capacity, simple structure, and wide bandwidth, and are widely used in radio frequency communication systems.

[0003] The conventional ridged waveguide slotted filter is a waveguide band-pass filter implementation scheme relatively close to this patent. Its structure is as Figure 1 shown. There are slot teeth structures on the ridges of the ridged waveguide, and in a cross-section parallel to the bottom surface, a structure in which slots and teeth are arranged alternately along the axis of the waveguide is presented. The structure is simple and has good broadband characteristics.

[0004] Disadvantages of the prior art:

[0005] Although traditional waveguide filters have advantages such as low loss, good selectivity, and wide passband, they are affected by higher-order modes at the high-frequency end, resulting in poor out-of-band rejection performance. Moreover, with the increase in frequency, parasitic passbands will appear earlier. For broadband systems, filters not only require broadband performance but also good wide-stopband characteristics. The parasitic passbands of common waveguide filters are relatively close to the main passband and appear at 1.5 times the center frequency, making it difficult to meet the requirements of modern broadband communication systems for out-of-band rejection. Summary of the Invention

[0006] In view of the above technical problems existing in the prior art, the present invention proposes a high-selectivity waveguide filter with a tapered coupling structure, which is reasonably designed, overcomes the deficiencies of the prior art, and has good effects.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A high-selectivity waveguide filter with a tapered coupling structure includes a standard rectangular waveguide, a double-tapered waveguide, and a double-tapered resonant coupling structure; the overall structure of the waveguide filter is a triple-symmetry structure.

[0009] Preferably, the dual-gradual-resonance coupling structure adopts a multi-stage ridge waveguide gradual form. Both its resonance unit and coupling unit are composed of rectangular waveguides. The height and width of both the resonance unit and coupling unit gradually decrease towards the center point of the filter from the dual-gradual waveguide structure, forming an electric field enhancement structure, and simultaneously achieving wideband bandpass and harmonic suppression.

[0010] Preferably, the dual-gradual waveguides are cascaded in a multi-stage stepped form, and their height and width gradually decrease towards the resonance coupling structure direction from the standard rectangular waveguide port simultaneously, realizing the transition matching between the standard waveguide port and the dual-gradual resonance coupling structure.

[0011] The beneficial technical effects brought by the present invention:

[0012] (1) The present invention designs a dual-gradual resonance coupling structure, with the ridge waveguide as the prototype, realizing the wideband performance of the filter. At the same time, an inductance enhancement and capacitance enhancement structure is formed, adjusting the high and low characteristic impedances of the waveguide, meeting the requirements of higher high-order mode suppression, achieving harmonic suppression up to 2.5 times the center frequency of the filter, obtaining ideal out-of-band suppression performance at the high-frequency end, and reducing the longitudinal size of the filter.

[0013] (2) The present invention adopts the form of stepped transformation of the dual-gradual waveguide structure to realize the transition between the standard waveguide ports at the input and output ends of the filter and the resonance coupling structure, ensuring the wideband matching characteristics of the filter. Description of the Drawings

[0014] Figure 1 Schematic diagram of the waveguide filter structure with the ridge waveguide slotted method;

[0015] Figure 2 Schematic diagram of the high-selectivity waveguide filter structure with gradual coupling;

[0016] Figure 2 In (a) is the three-dimensional structure diagram of the waveguide filter; (b) is the top view of the waveguide filter; (c) is the front view of the waveguide filter. Detailed Embodiments

[0017] The present invention will be further described in detail below in conjunction with the drawings and specific embodiments:

[0018] The present invention adopts a novel filter based on the waveguide gradual theory, and its structure is as Figure 2 shown. This waveguide filter is composed of three parts: a standard rectangular waveguide, a dual-gradual waveguide, and a dual-gradual resonance coupling structure. From left to right, the filter shown is composed of a standard rectangular waveguide, a dual-gradual waveguide, a dual-gradual resonance coupling structure, a dual-gradual waveguide, and a standard rectangular waveguide cascaded in sequence, and its structure is a triple-symmetry structure. From the standard waveguide port towards the center point of the filter, the height and width dimensions of each stage of waveguide and resonance coupling structure gradually decrease step by step.

[0019] The double-gradient waveguide is a transition matching structure between a standard waveguide port and a resonant coupling structure, including multiple-stage transmission lines, which are connected to the standard waveguide port at the input and output ends, and the aperture matches that of the standard waveguide port; the double-gradient waveguide changes in a stepped manner, and the height and width dimensions of each stage of the waveguide gradually decrease from the standard waveguide port towards the resonant coupling structure direction, realizing broadband matching between the resonant cavity and the standard waveguide port.

[0020] The double-gradient resonant coupling structure is composed of a resonant unit and a coupling unit, adopting the form of a ridge waveguide double-gradient. The cutoff frequency of the main mode of the ridge waveguide is lower than that of the ordinary waveguide, and the frequency of the first higher-order mode is higher than that of the ordinary waveguide. By adjusting the dimensions of several coupling units close to the gradient waveguide to make their height higher and length shorter, broadband performance can be achieved. At the same time, the resonant coupling structure all adopts the form of a rectangular waveguide to realize high and low impedance transformation, suppress higher-order modes, and achieve better wide stopband characteristics. The height and width of the resonant coupling structure both gradually decrease from the gradient waveguide towards the center point direction, which can be equivalent to the form of a resonant window diaphragm, and at the same time form an inductance enhancement and capacitance enhancement structure, strengthening the out-of-band suppression degree at the high-frequency end, and realizing the performance of wideband and high selectivity at the same time.

[0021] Key points of the present invention:

[0022] (1) Broadband characteristics: By adjusting the length and height of the resonant coupling structure, especially the dimensions of the coupling units close to the gradient waveguide to make their height higher and length shorter, broadband performance can be achieved.

[0023] (2) High selectivity: Adopting a double-gradient resonant coupling structure with a ridge waveguide as the prototype, while realizing broadband characteristics, the high and low characteristic impedances of the waveguide are adjusted, higher-order modes are suppressed, and wide stopband performance is achieved. The double-gradient form decreases in size from the waveguide port direction towards the center, enhancing the electric field density, achieving an ideal out-of-band suppression effect, realizing a higher out-of-band suppression degree compared with a single-gradient structure, and at the same time ensuring broadband performance.

[0024] Protected points of the present invention:

[0025] (1) Double-gradient waveguide resonant coupling structure: The double-gradient resonant coupling structure proposed by the present invention adopts the form of a ridge waveguide gradient, and both the height and width decrease from the gradient waveguide towards the filter center direction, forming an electric field enhancement structure, realizing a higher out-of-band suppression degree, while suppressing the parasitic mode coupling intensity, realizing that the out-of-band suppression of the filter at the high-frequency far end can reach 2.5 times the center frequency, achieving the out-of-band suppression performance of wide stopband and high suppression degree, and at the same time ensuring the broadband characteristics of the filter.

[0026] Certainly, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions, or substitutions made by those skilled in the art within the scope of the essence of the present invention should also fall within the protection scope of the present invention.

Claims

1. A highly selective waveguide filter with a gradual coupling, characterized in that: It includes three parts: a standard rectangular waveguide, a double-gradient waveguide and a double-gradient resonant cavity coupling structure; the waveguide filter as a whole is a triple symmetrical structure.

2. The tapered coupling high selectivity waveguide filter according to claim 1, characterized in that: The double-gradient resonant coupling structure adopts a multi-level ridge waveguide gradient form. Its resonant unit and coupling unit are both composed of rectangular waveguides. The height and width of the resonant unit and the coupling unit gradually decrease from the double-gradient waveguide structure toward the center point, forming an electric field enhancement structure, while achieving wide passband and harmonic suppression.

3. The tapered coupling high selectivity waveguide filter according to claim 2, characterized in that: The double gradient waveguide is cascaded in a multi-step form, and its height and width gradually decrease from the standard rectangular waveguide port to the center of the resonant coupling structure, thereby achieving transition matching between the standard waveguide port and the double gradient resonant coupling structure.

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