Compact high-selectivity substrate integrated waveguide triangular cavity wide stopband filter

Abstract

The present invention belongs to the technical field of microwave filters. Disclosed is a compact high-selectivity substrate integrated waveguide triangular cavity wide stopband filter, which is successively provided, from top to bottom, with an upper metal layer, a middle dielectric layer substrate, and a lower metal layer; the upper metal layer is connected to the lower metal layer via metalized via holes, and the upper metal layer, the lower metal layer and the middle dielectric layer substrate collectively form dielectric-filled cavities; all of the cavities are in triangular shapes and only comprise isosceles right-angled triangular cavities and equilateral triangular cavities, the right-angled side lengths of the isosceles right-angled triangular cavities being linearly related to the side lengths of the equilateral triangular cavities, and the cavities of the whole filter being a pentagonal structure. The present invention combines the harmonic interleaving technology and the harmonic coupling technology, provides the relationship between the right-angled side lengths of substrate integrated waveguide isosceles right-angled triangular cavities and the side lengths of the substrate integrated waveguide equilateral triangular cavities, and not only has a compact and simple structure, but also simplifies design steps, thereby having important application prospects.

Description

A compact, highly selective substrate-integrated waveguide triangular cavity wide-stopband filter Technical Field

[0001] The invention belongs to the technical field of microwave filters, and in particular relates to a compact, highly selective substrate integrated waveguide triangular cavity wide stopband filter. Background Art

[0002] Wireless and military communications are placing increasing demands on filter performance. As an integral part of RF microwave front-end circuits, filter parameters directly impact the performance of the entire front-end circuit. Substrate-integrated waveguide technology has made significant progress since its introduction.

[0003] Substrate integrated waveguide technology was proposed by combining the advantages of both microstrip circuits and waveguides. It has the characteristics of high quality factor and high power capacity of waveguides, as well as the characteristics of compact structure and easy integration of planar microstrip circuits, filling the technical gap between planar microstrip / stripline and non-planar waveguide / dielectric resonator.

[0004] The principle of harmonic interleaving is to design the filter so that the resonant modes used to construct the passband have the same frequency while staggering the other spurious resonant frequencies. When multiple resonators are coupled and cascaded to form a filter, harmonic levels can be suppressed. Its advantages are that it does not require any additional components and does not require consideration of signal coupling. Its disadvantages are that it is only applicable to narrow bandwidths and weak coupling, and that spurious levels are uncontrollable, and it is impossible to reduce all harmonic levels to below the ideal value.

[0005] Harmonic coupling control technology, by properly selecting the coupling locations between resonators or between ports and input resonators, can precisely control the coupling strength of harmonic signals, achieving stopband suppression when harmonic coupling is zero or very weak. Coupling matrix synthesis can also be used to obtain the coupling matrix corresponding to the stopband response, which can then be applied to higher harmonics to achieve spurious suppression. This approach has the advantage of not requiring additional distributed components. However, it requires considering the coupling of both the fundamental frequency and harmonics, which increases the complexity of circuit design.

[0006] In cross-coupling technology, if the signals transmitted on two different physical transmission paths have the same amplitude but opposite phase, their energy cancels each other, thus creating a transmission zero on the imaginary axis. However, positive and negative coupling must be implemented simultaneously to provide opposite phases.

[0007] There are many deficiencies in the existing substrate integrated waveguide wide stopband filters: 1. Most of the existing research on substrate integrated waveguide wide stopband filters uses rectangular cavities and square cavities, and rarely uses triangular cavities. So far, there is no filter with wide stopband performance that uses both isosceles right-angled triangular cavities and equilateral triangular cavities at the same time. 2. Most of the existing substrate integrated waveguide wide stopband filters introduce special electrical coupling or hybrid coupling structures to achieve the negative coupling required for cross-coupling. More parameters make the process of adjusting the filter parameters relatively time-consuming. 3. The common substrate integrated waveguide filter that is realized by combining rectangular cavities and square cavities has an operating frequency that is related to the side length of the square cavity, the length and width of the rectangular cavity, and the relationship between the side length of the rectangular cavity and the side length of the square cavity is not linear, so it takes more time to adjust the overall size of the filter.

[0008] Summary of the Invention

[0009] In order to solve the above technical problems, the present invention provides a high-selectivity substrate integrated waveguide triangular cavity wide stopband filter with a simple and compact structure and easy design and processing. It is a new substrate integrated waveguide wide stopband filter. While using a triangular cavity structure to simplify the overall size determination of the substrate integrated waveguide wide stopband filter, cross-coupling technology, harmonic interleaving technology and harmonic coupling control technology are combined to simplify the structure of the filter, improve the selectivity of the filter passband, widen the stopband suppression of the filter, and improve the availability of the compact high-selectivity substrate integrated waveguide triangular cavity wide stopband filter.

[0010] In order to achieve the above object, the present invention is achieved through the following technical solutions:

[0011] The present invention is a compact high-selectivity substrate integrated waveguide triangular cavity wide stopband filter. The high-selectivity substrate integrated waveguide triangular cavity wide stopband filter is sequentially provided with an upper metal layer, an intermediate dielectric layer substrate, a lower metal layer, and an upper metal layer from top to bottom. The geometric centers of the patterns of the intermediate dielectric layer substrate and the lower metal layer are all on the same straight line. The upper metal layer is connected to the lower metal layer through a metallized via and forms a cavity filled with a dielectric together with the intermediate dielectric layer substrate. The outline of each cavity is determined by the metallized via. The shape of the cavity is triangular and is composed only of an isosceles right-angled triangular cavity and an equilateral triangular cavity. The right-angled side length of the isosceles right-angled triangular cavity is linearly related to the side length of the equilateral triangular cavity. The cavity of the entire filter has a pentagonal structure.

[0012] A further improvement of the present invention is that the linear relationship between the length of the right angle side of the isosceles right triangle cavity and the length of the side of the equilateral triangle cavity is:

[0013] Where: a1eff is the length of the right angle side of the isosceles right triangle cavity, aeff is the length of the side of the equilateral triangle cavity. By determining the length of any side of any cavity, the size of the entire filter can be determined.

[0014] A further improvement of the present invention is that: the upper metal layer is also connected to two feed lines, the cavity where the feed lines are located is and is only two adjacent and mutually coupled equilateral triangular cavities, a coupling gap is provided on both sides of each feed line, the width of the coupling gap is 0.2 mm, and the length of the coupling gap is 2.5 mm. The entire filter is a single-layer structure, the feeding position is at the center of one side of the equilateral triangular cavity, and all the coupling windows inside are offset from the center of the side length where they are located.

[0015] A further improvement of the present invention is that there is a coupling window formed by a pair of metallized vias between each two adjacent cavities, and electrical coupling is achieved by coupling between the working modes of the isosceles right triangle cavity and the equilateral triangle cavity.

[0016] A further improvement of the present invention is that: the diameter of the metallized via is 0.5 mm, the spacing between each two adjacent metallized vias is 1 mm except for the coupling window, the width of the coupling window between the equilateral triangle cavity connected to the feed line at the cut corner and the isosceles right-angle triangle cavity is 4.19 mm, and the offset of the coupling window from the center position of the side on which it is located is 3.7 mm. In counterclockwise order, the width of the coupling window is 4.03 mm, 3.4 mm, and 2.3 mm, respectively, and in counterclockwise order, the offset of the coupling window from the center position of the side on which it is located is 3.7 mm, 2 mm, and 2 mm, respectively.

[0017] A further improvement of the present invention is that the length of the hypotenuse of the isosceles right triangle cavity is slightly smaller than the sum of the side lengths of the two equilateral triangle cavities coupled with it, and the right-angled vertex of the isosceles right triangle cavity faces the vertices of the two equilateral triangle cavities coupled with it.

[0018] A further improvement of the present invention is that the filter of the present invention has both electrical coupling and magnetic coupling, generates a transmission zero point on each side of the passband, and improves the selectivity of the substrate integrated waveguide triangular cavity wide stopband filter.

[0019] The beneficial effects of the present invention are:

[0020] The present invention fills the patent gap in the triangular cavity aspect of high-selectivity substrate integrated waveguide wide-stopband filters. Compared with traditional high-selectivity substrate integrated waveguide wide-stopband filters, the filter coupling structure is simpler. By using harmonic interleaving technology and harmonic coupling control technology, the electrical coupling required to generate two transmission zeros to improve selectivity and the suppression of stray harmonics are achieved, achieving the stopband width suppressed by traditional high-selectivity substrate integrated waveguide wide-stopband filters.

[0021] The present invention innovatively applies a triangular cavity to the design of a substrate-integrated waveguide filter, thereby simplifying the determination of the overall dimensions of the substrate-integrated waveguide filter at any operating frequency and reducing the overall dimensions of the substrate-integrated waveguide filter. The smaller size, simpler structure, and easier determination of the overall dimensions of the filter greatly increase the practicality of the present invention in wireless communication systems.

[0022] The present invention combines harmonic interleaving technology with harmonic coupling technology, and provides the relationship between the right-angle side length of the substrate-integrated waveguide isosceles right-angle triangle cavity and the side length of the substrate-integrated waveguide equilateral triangle cavity. This not only has a compact and simple structure, but also simplifies the design steps. The high selectivity and wide stopband suppression make the present invention have important application prospects in filtering out interference signals generated by wireless communication applications and parasitic clutter signals generated inside transceivers. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG1 is a schematic structural diagram of the present invention.

[0024] FIG2 is a top view of the present invention.

[0025] FIG3 is a bottom view of the present invention.

[0026] FIG4 is an S-parameter diagram of the filter of the present invention.

[0027] FIG5 is a coupling topology diagram of the present invention.

[0028] FIG6 is a coupling matrix of the present invention. DETAILED DESCRIPTION

[0029] The following drawings illustrate embodiments of the present invention. For clarity, many practical details are included in the following description. However, it should be understood that these practical details are not intended to limit the present invention. In other words, in some embodiments of the present invention, these practical details are not essential. Furthermore, to simplify the drawings, some commonly used structures and components are depicted in simplified schematic form.

[0030] As shown in Figure 1, the present invention is a compact, highly selective, substrate-integrated waveguide triangular cavity wide-bandstop filter. It primarily consists of two metal layers and one dielectric layer, including an upper metal layer, a middle dielectric substrate, and a lower metal layer. The middle dielectric substrate is preferably made of 0.508mm-thick Rogers RT5880, which has a dielectric constant of 2.2 and a loss tangent of 0.0009. The filter's outer contour is defined by a square with a side length of no less than 59mm. The top view shows a 60° bevel cut at the lower right corner. The short side of the cut corner is no longer than 15mm and does not overlap with the cavity metal patch.

[0031] The upper metal layer and the lower metal layer are connected by metallized vias 2 and combined with the intermediate dielectric substrate to form a cavity. The cut angle is consistent with the outer contours of the intermediate dielectric substrate and the lower metal layer. The contour of each cavity is determined by the metallized vias with a diameter of 0.5mm. The shape of the cavity is triangular and consists only of isosceles right-angled triangle cavities and equilateral triangle cavities. The right-angled side length of the isosceles right-angled triangle cavity is linearly related to the side length of the equilateral triangle cavity, specifically:

[0032] Where a1eff is the length of the right angle of the isosceles right triangle cavity, and aeff is the length of the side of the equilateral triangle cavity. The right angle of the substrate-integrated waveguide isosceles right triangle cavity is approximately 1.369 times the side length of the substrate-integrated waveguide equilateral triangle cavity. Determining the length of any side of any cavity determines the dimensions of the entire filter, reducing filter design complexity and simplifying the design process for highly selective substrate-integrated waveguide triangular cavity wide-stopband filters.

[0033] As shown in Figure 2-3, the upper metal layer is composed of an upper metal layer with four triangular cavities and a feed line. The cavities where the two feed lines of the upper metal layer are located are and are only two adjacent and mutually coupled equilateral triangular cavities. A coupling gap 5 is provided on both sides of each feed line. The width of the coupling gap 5 is 0.2 mm and the length of the coupling gap 5 is 2.5 mm. The upper metal layer of the entire cavity is composed of three equilateral triangles and one isosceles right triangle, presenting a pentagon.

[0034] The upper metal layer is a complete plane, with no other slots or slits except for the metallized vias and coupling slots on either side of the feeder. Coupling of the entire filter is achieved through a coupling window formed by a pair of widely spaced metallized vias, simplifying the design of traditional electrical coupling structures.

[0035] Between each adjacent cavity, a coupling window 6 is formed by a pair of metallized vias 2. All coupling is achieved through a simple coupling window, without the introduction of specialized electrical coupling structures or hybrid coupling structures. Electrical coupling is achieved solely through coupling between the operating modes of the substrate-integrated waveguide isosceles right-angle triangle cavity and the substrate-integrated waveguide equilateral triangle cavity. This eliminates the need for electrical coupling structure design, simplifying filter design.

[0036] The entire filter has a single-layer structure, with the feed position located at the center of one side of the equilateral triangle cavity. All internal coupling windows are offset from the center of their respective sides. Except for the coupling windows, the spacing between each adjacent metallized via 2 is 1 mm. The coupling window 6 between the equilateral triangle cavity connected to the feed line at the cut corner and the isosceles right-angle triangle cavity is 4.19 mm wide, and the offset of the coupling window 6 from the center of its side is 3.7 mm. In counterclockwise order, the widths of the coupling window 6 are 4.03 mm, 3.4 mm, and 2.3 mm, respectively. In counterclockwise order, the offsets of the coupling window 6 from the center of its side are 3.7 mm, 2 mm, and 2 mm, respectively. While ensuring optimal coupling in the operating mode, several spurious modes near the operating mode are intrinsically suppressed, forming a wide stopband filter. The shape and dimensions of the lower metal layer are identical to those of the bottom surface of the dielectric plate to which it is connected.

[0037] The hypotenuse of the isosceles right-angled triangular cavity is slightly shorter than the sum of the side lengths of the two equilateral triangular cavities coupled to it, and the right-angled vertex of the isosceles right-angled triangular cavity directly faces the vertices of the two equilateral triangular cavities coupled to it. The filter of the present invention has both electrical and magnetic coupling, creating a transmission zero on each side of the passband, thereby improving the selectivity of the substrate-integrated waveguide triangular cavity wide-stopband filter.

[0038] As shown in Figure 4, the filter's 3dB bandwidth reaches 1.5%, or 9.92GHz-10.07GHz. Return loss within the operating bandwidth is consistently below -20dB, with a minimum insertion loss of 1.24dB. The passband zeros are located at 9.86GHz and 10.12GHz, respectively. Because several spurious modes close to the operating mode frequency are suppressed in the upper stopband, the filter's 20dB suppression stopband bandwidth reaches 2.01f0.

[0039] In Figure 5, node S represents the source, node L represents the load, and nodes 1, 2, 3, and 4 represent the corresponding four cavities. Solid lines connecting nodes represent magnetic coupling, while dashed lines represent electrical coupling. Nodes 1 to 2, 2 to 3, and 3 to 4 are all direct coupling paths. Node 1 to 4 is a cross-coupling path.

[0040] The coupling coefficients in the coupling matrix in Figure 6 not only correspond to the key dimensions of the proposed filter and determine their size, but also reflect the coupling between the various cavities and the presence of cross-coupling. Generally, a positive coupling coefficient corresponds to magnetic coupling, while a negative coupling coefficient corresponds to electrical coupling or a coupling with the opposite phase response to the positive coupling.

[0041] This invention combines harmonic interleaving and harmonic coupling techniques and provides a relationship between the lengths of the right angles of a substrate-integrated waveguide isosceles right-angled triangle cavity and the lengths of its sides. This results in a compact and simple structure and streamlines the design process. Its high selectivity and wide stopband rejection make this invention promising for filtering interference signals generated in wireless communication applications and parasitic clutter signals generated within transceivers.

[0042] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A compact high-selectivity substrate integrated waveguide triangular cavity width stopband filter, wherein the high-selectivity substrate integrated waveguide triangular cavity width stopband filter is sequentially provided with an upper metal layer, an intermediate dielectric layer substrate (1), and a lower metal layer from top to bottom, wherein the geometric centers of the upper metal layer, the intermediate dielectric layer substrate (1) and the lower metal layer pattern are on the same straight line, the upper metal layer is connected to the lower metal layer through a metallized via (2), and together with the intermediate dielectric layer substrate (1) forms a cavity filled with a dielectric, and the contour of each cavity is uniform. Determined by the metallized via (2), the shape of the cavity is a triangle and is only composed of an isosceles right-angled triangle cavity and an equilateral triangle cavity. The length of the right-angled side of the isosceles right-angled triangle cavity is linearly related to the length of the side of the equilateral triangle cavity. The upper metal layer of the cavity of the entire filter is composed of three equilateral triangles and one isosceles right-angled triangle, presenting a pentagon. The length of the hypotenuse of the isosceles right-angled triangle cavity is slightly smaller than the sum of the side lengths of the two equilateral triangle cavities coupled to it. The right-angled vertex of the isosceles right-angled triangle cavity is opposite to the vertices of the two equilateral triangle cavities coupled to it.

2. A compact, highly selective substrate integrated waveguide triangular cavity wide stopband filter according to claim 1, characterized in that: The linear relationship between the right angle side length of the isosceles right triangle cavity and the side length of the equilateral triangle cavity is: Where: a1eff is the length of the right angle side of the isosceles right triangle cavity, aeff is the length of the side of the equilateral triangle cavity. By determining the length of any side of any cavity, the size of the entire filter can be determined.

3. A compact, highly selective substrate integrated waveguide triangular cavity wide stopband filter according to claim 1, characterized in that: The upper metal layer connects two feed lines, and the cavity where the feed lines are located is and is only two adjacent and mutually coupled equilateral triangular cavities. A coupling slot (5) is provided on both sides of each feed line, and the width of the coupling slot (5) is 0.2 mm, and the length of the coupling slot (5) is 2.5 mm. The entire filter is a single-layer structure, and the feeding position is at the center of one side of the equilateral triangular cavity.

4. A compact, highly selective substrate integrated waveguide triangular cavity wide stopband filter according to claim 3, characterized in that: A coupling window (6) formed by a pair of metallized vias (2) is arranged between each two adjacent cavities, and electrical coupling is achieved by coupling the isosceles right-angle triangle cavity and the equilateral triangle cavity, and all the coupling windows inside are offset from the center of the side length where they are located.

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