A millimeter-wave SIW bandpass filter

Abstract

This invention provides a millimeter-wave SIW bandpass filter, comprising: a first dielectric substrate and a second dielectric substrate stacked vertically, and a top metal layer disposed on the upper surface of the first dielectric substrate, an intermediate metal layer between the first dielectric substrate and the second dielectric substrate, and a bottom metal layer disposed on the lower surface of the second dielectric substrate. This technical solution achieves low insertion loss, high roll-off characteristics, and wide stopband suppression through a multi-layer SIW structure and feeding via a coplanar waveguide with coupled branches. The intermediate metal layer is designed with a coupling window, and metal pillars and coupling gaps are loaded.

Description

Technical Field

[0001] This invention relates to the field of microwave communication technology, and in particular to a millimeter-wave SIW bandpass filter. Background Technology

[0002] As a core component of the radio frequency (RF) front-end, the technological evolution of filters has always been closely related to the development needs of communication systems. Early metal cavity filters dominated the market due to their high Q-value and strong anti-interference capabilities, but their large size and complex machining processes severely restricted the miniaturization of modern communication equipment. In the early 21st century, microstrip filters emerged due to their planar design advantages; however, significant radiation loss and relatively low Q-value at high frequencies limited their application in more communication scenarios. Against this backdrop, substrate integrated waveguide (SIW) technology, by combining the electromagnetic characteristics of metal cavities with the integration advantages of planar circuits, has become a key technology for overcoming the performance bottlenecks of traditional filters.

[0003] Multilayer SIW filters achieve size compression through vertical stacking, but problems such as increased passband ripple and insufficient stopband suppression due to insufficient interlayer coupling efficiency remain to be solved. While the introduction of multimode resonant technology improves frequency selectivity, the nonlinear coupling of resonant modes easily induces out-of-band parasitic responses, especially causing signal crosstalk when multiple frequency bands operate together. Microstrip-slot hybrid structures can enhance coupling flexibility. Furthermore, the uniform electromagnetic field distribution formed by the regular arrangement of traditional metal pillars is difficult to meet complex stopband suppression requirements, especially in high-frequency applications where high-order harmonic interference is likely to occur. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a millimeter-wave SIW bandpass filter, which achieves low insertion loss, high roll-off characteristics and wide stopband suppression through a multi-layer SIW structure and a coplanar waveguide with coupled stubs, a coupling window designed in the middle metal layer and a loaded metal pillar.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a millimeter-wave SIW bandpass filter, comprising: a first dielectric substrate and a second dielectric substrate stacked on top of each other, and a top metal layer disposed on the upper surface of the first dielectric substrate, an intermediate metal layer between the first dielectric substrate and the second dielectric substrate, and a bottom metal layer disposed on the lower surface of the second dielectric substrate. The first dielectric substrate and the second dielectric substrate are respectively provided with a plurality of metallized through holes, which form a cavity; The top and bottom metal layers are each provided with a coplanar waveguide feeding structure. The coplanar waveguide feeding structure includes a coplanar waveguide transmission line and a coupling stub connected to the end of the coplanar waveguide transmission line. The coplanar waveguide transmission line extends into the cavity formed by the metallized via; The intermediate metal layer has a coupling window, and coupling gaps are formed at both ends of the coupling window. A rectangular metal patch is provided at the center of the coupling window; Multiple loading metal pillars are also disposed within the cavities of the first and second dielectric substrates, and the loading metal pillars are used to introduce transmission zero points.

[0006] In a preferred embodiment, the coupling gap consists of two orthogonal gaps.

[0007] In a preferred embodiment, a row of metallized vias is provided on both sides of the coplanar waveguide feeding structure, the metallized vias being used to reduce radiation loss.

[0008] In a preferred embodiment, two sets of metallized vias are provided at the centerline of the cavity, and the two sets of metallized vias are used to suppress parasitic modes outside the low-frequency passband.

[0009] In a preferred embodiment, metallized vias are provided at the four corners of the cavity, and the metallized vias are used to improve impedance matching performance.

[0010] In a preferred embodiment, both the first dielectric substrate and the second dielectric substrate are Rogers RT5880 dielectric insulating substrates with a thickness of 0.254 mm.

[0011] In a preferred embodiment, the thickness of the top metal layer, the middle metal layer, and the bottom metal layer is 0.03 mm.

[0012] In a preferred embodiment, the filter has a center frequency of 30.6 GHz, an insertion loss in the passband better than -0.4 dB, a return loss better than -18 dB, a 3 dB relative bandwidth of 21.30%, a low-frequency stopband rejection better than -18 dB, and a high-frequency stopband rejection better than -20 dB.

[0013] In a preferred embodiment, the loading metal pillars are respectively disposed at different positions inside the cavity to generate two transmission zeros on both sides of the passband.

[0014] Compared with existing technologies, this invention has the following advantages: The invention employs a multi-layer SIW structure combined with coplanar waveguide coupling stub feeding, effectively reducing radiation loss in the millimeter-wave band and improving impedance matching characteristics within the passband. Orthogonal coupling slots are opened at both ends of the coupling window in the middle metal layer of this invention, achieving efficient inter-layer energy coupling over a wide frequency band and improving stopband performance. A rectangular metal patch is loaded at the center of the coupling window of this invention, further optimizing return loss within the passband. Metal pillars are loaded at specific locations within the cavity of this invention, introducing transmission zeros and significantly improving roll-off characteristics and stopband suppression capabilities on both sides of the passband. This invention has a small overall size, is easy to integrate, and has relatively low processing costs, making it suitable for millimeter-wave wireless communication, satellite, and radar systems. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the top-level structure parameters of an ultra-wideband microstrip bandpass filter. Figure 2 This is a schematic diagram of the intermediate layer structure parameters of an ultra-wideband microstrip bandpass filter; Figure 3 This is a side view schematic diagram of an ultra-wideband microstrip bandpass filter. Figure 4 The resonant curve of an ultra-wideband microstrip bandpass filter; Figure 5 Smith impedance curve for an ultrawideband microstrip bandpass filter; Among them, 1-coplanar waveguide transmission line, 2-coupled stub, 3-metallized via, 4-rectangular metal patch, 5-coupled slot, 6-loaded metal pillar. Detailed Implementation

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0017] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0018] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application; as used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise; furthermore, it should be understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0019] This invention discloses a broadband bandpass filter operating from 26.96 GHz to 33.39 GHz, comprising: a first dielectric substrate and a second dielectric substrate stacked on top of each other, and a top metal layer disposed on the upper surface of the first dielectric substrate, an intermediate metal layer between the first dielectric substrate and the second dielectric substrate, and a bottom metal layer disposed on the lower surface of the second dielectric substrate. The first dielectric substrate and the second dielectric substrate are respectively provided with a plurality of metallized through holes 3, and the metallized through holes 3 form a cavity; The top and bottom metal layers are each provided with a coplanar waveguide feeding structure. The coplanar waveguide feeding structure includes a coplanar waveguide transmission line 1 and a coupling stub 2 connected to the end of the coplanar waveguide transmission line. The coplanar waveguide transmission line 1 extends into the cavity formed by the metallized via 3; The intermediate metal layer has a coupling window, and coupling gaps 5 are respectively formed at both ends of the coupling window. A rectangular metal patch 4 is provided at the center of the coupling window; Multiple loading metal pillars 6 are also provided in the cavities of the first dielectric substrate and the second dielectric substrate, and the loading metal pillars 6 are used to introduce transmission zero points.

[0020] This filter uses a Rogers RT5880 dielectric insulating substrate with a thickness of 0.254 mm and a metal layer thickness of 0.03 mm. It has a relative permittivity of 2.2 and a loss tangent of 0.0009. It consists of two 0.254 mm thick dielectric layers, with an intermediate metal layer that transmits energy through coupling windows and gaps. The top and bottom metal layers employ a coplanar waveguide (CPW) feeding structure. Different copper plating patterns are applied to the top, bottom, and intermediate metal layers to obtain the filter. The design pattern of the top metal layer is shown below. Figure 1 As shown, the bottom and top metal structures of the filter are symmetrical, and the feed lines are in opposite directions.

[0021] The overall size of the filter is 15 × 8.2 × 0.518 mm³. The filter has an insertion loss of -0.4 dB at its center frequency of 30.6 GHz, a passband return loss better than -18 dB, a 3 dB relative bandwidth of 21.30% (26.9 GHz to 33.4 GHz), a low-frequency stopband rejection of -18 dB (0 GHz to 24.5 GHz), and a high-frequency stopband rejection of -20 dB (32.6 GHz to 41.2 GHz). The multilayer SIW bandpass filter structure proposed in this invention has a relatively low overall manufacturing cost. The main application scenarios for this design are wireless communication, satellite, and radar systems in the millimeter-wave band. Due to its small overall size, the filter is also easy to integrate, meeting the current requirements for miniaturization and integration of electronic devices.

[0022] The loading metal pillars inside the filter cavity and the coupling window design of the intermediate metal layer introduce two zeros into the filter's stopband, optimizing stopband suppression characteristics. This design is primarily intended for applications in millimeter-wave wireless communication, satellite, and radar systems. Due to its small overall size and single-layer planar microstrip structure, this filter is easy to integrate, meeting current requirements for miniaturization and integration in electronics, and possesses considerable potential for future applications.

[0023] like Figure 1-3 As shown, metallized vias 3 are distributed within the upper and lower dielectric substrates to form a cavity. Two sets of metallized vias 6 are located at the center line of the cavity to suppress low-frequency out-of-band parasitic modes; metallized vias 6 are located at the four corners of the cavity to improve impedance matching.

[0024] Table 1 shows the key structural parameters (unit: mm) of the filter in this embodiment. These parameters represent the optimal values ​​for overall performance, but the present invention is not limited to these specific values.

[0025] Table 1. Optimal characteristic parameters of the filter (unit: mm)

[0026] Figure 4 The resonant curve of this ultra-wideband microstrip bandpass filter is shown. The overall passband frequency ranges from 26.9 GHz to 33.4 GHz. The insertion loss at the passband center frequency of 30.15 GHz is 0.4 dB. The zeros on both sides of the passband reach -38.25 dB and -47.46 dB at 21.6 GHz and 37.1 GHz, respectively. The low-frequency stopband maintains a reflection below -18 dB from 0 to 24.07 GHz, and the high-frequency stopband maintains a reflection below -20 dB from 36.98 to 40.95 GHz.

[0027] Figure 5 The impedance curve shows that the filter's input impedance at the center frequency of 30.15 GHz is 1.0175-j*0.1342Ω, and the normalized input impedances are 0.6536-j*0.3123Ω at 26.9 GHz and 0.4369-j*2.1194Ω at 33.4 GHz. At this point, the filter has good impedance matching characteristics within the passband.

[0028] The above description is an embodiment of the present invention. For those skilled in the art, any equivalent changes, modifications, substitutions and variations made in accordance with the teachings of the present invention without departing from the principles and spirit of the present invention should be covered by the present invention.

Claims

1. A millimeter-wave SIW bandpass filter, characterized in that, include: A first dielectric substrate and a second dielectric substrate are stacked on top of each other, and a top metal layer, an intermediate metal layer between the first dielectric substrate and the second dielectric substrate, and a bottom metal layer are respectively disposed on the upper surface of the first dielectric substrate. The first dielectric substrate and the second dielectric substrate are respectively provided with a plurality of metallized through holes, which form a cavity; The top and bottom metal layers are each provided with a coplanar waveguide feeding structure. The coplanar waveguide feeding structure includes a coplanar waveguide transmission line and a coupling stub connected to the end of the coplanar waveguide transmission line. The coplanar waveguide transmission line extends into the cavity formed by the metallized via; The intermediate metal layer has a coupling window, and coupling gaps are formed at both ends of the coupling window. A rectangular metal patch is provided at the center of the coupling window; Multiple loading metal pillars are also disposed within the cavities of the first and second dielectric substrates. These loading metal pillars are used to introduce transmission zero points and optimize reflection performance.

2. The millimeter-wave SIW bandpass filter according to claim 1, characterized in that, The coupling gap consists of two orthogonal gaps.

3. A millimeter-wave SIW bandpass filter according to claim 1, characterized in that, A row of metallized vias is provided on both sides of the coplanar waveguide feeding structure. The metallized vias are used to reduce radiation loss.

4. A millimeter-wave SIW bandpass filter according to claim 1, characterized in that, Two sets of metallized vias are provided at the centerline of the cavity. These two sets of metallized vias are used to suppress parasitic modes outside the low-frequency passband.

5. A millimeter-wave SIW bandpass filter according to claim 1, characterized in that, Metallized through holes are provided at the four corners of the cavity, and the metallized through holes are used to improve impedance matching performance.

6. A millimeter-wave SIW bandpass filter according to claim 1, characterized in that, Both the first dielectric substrate and the second dielectric substrate are Rogers RT5880 dielectric insulating substrates with a thickness of 0.254 mm.

7. A millimeter-wave SIW bandpass filter according to claim 1, characterized in that, The thickness of the top metal layer, the middle metal layer and the bottom metal layer is 0.03 mm.

8. A millimeter-wave SIW bandpass filter according to claim 1, characterized in that, The filter has a center frequency of 30.6 GHz, an insertion loss in the passband better than -0.4 dB, a return loss better than -18 dB, a 3 dB relative bandwidth of 21.30%, a low-frequency stopband rejection better than -18 dB, and a high-frequency stopband rejection better than -20 dB.

9. A millimeter-wave SIW bandpass filter according to claim 1, characterized in that, The loading metal pillars are respectively set at different positions inside the cavity to generate two transmission zero points on both sides of the passband.

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