BSSIR-based miniaturized microwave filter with bandwidth adjustable structure

Abstract

The invention discloses a BSSIR-based miniaturized microwave filter with a bandwidth adjustable structure. The BSSIR-based miniaturized microwave filter comprises two metal layers and a dielectric layer, the dielectric layer is arranged between the two metal layers; the lower metal layer is a grounding layer and comprises a grounding metal bottom plate and a lower metalized through hole, and the lower metalized through hole is formed in the center of the grounding metal bottom plate; the upper metal layer is a structural layer and specifically comprises a plurality of BSSIRs, a metal ring, an upper metalized through hole and a plurality of feed ports. The invention provides a miniaturized microwave filter based on an SIR with a bandwidth adjustable structure, which can realize high frequency selectivity and miniaturization of the filter, and can also realize bandwidth adjustability of the filter. According to the scheme of the filter, the low-impedance part of the SIR is cut into several parts, and then the switched capacitor is welded to the disconnected position; and bandwidth adjustment is realized by switching on and switching off the switch variable capacitor.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave radar communication, and in particular to a miniaturized microwave filter with a bandwidth adjustable structure based on BSSIR. Background Art

[0002] Filters are core components of modern radio frequency systems, such as radar and communications. Their primary function is to filter out unwanted clutter and harmonics, significantly improving system performance. In the microwave filter field, the primary design technologies are microstrip, substrate-integrated waveguide (SIW), and waveguide technology. Other technologies, such as SAW, MEMS, thin film, and LC (inductor-capacitor) filters, are limited to designing filters below the microwave frequency band and struggle to scale beyond it. Waveguides are three-dimensional structures, making them inherently unsuitable for miniaturized system integration. SIWs are larger than microstrip filters in the microwave frequency band, posing significant limitations when system volume and area resources are limited. Microstrip filters offer more flexible structural design in the microwave frequency band. Through structural folding, filters can be made very small, making them well-suited for PCB manufacturing, as well as for semiconductor and low-temperature co-fired ceramic (LTCC) processes.

[0003] A stepped impedance resonator (SIR) is a structure that uses microstrip transmission lines with different characteristic impedances to achieve resonance. By varying the impedance ratio of the SIR, the resonant frequency can be flexibly adjusted, effectively suppressing the filter's parasitic passband and enabling filter miniaturization.

[0004] In summary, the SIR-based microstrip filter design technology is the preferred technology for designing miniaturized, high-performance microwave filters.

[0005] Many radar systems are currently designed with adjustable bandwidth. During the initial detection phase, a narrowband transmitter is used to maintain a long detection range. Once the system approaches a target, a wideband transmitter is used to identify and lock onto it. This significantly reduces power consumption and maximizes operating time. However, existing adjustable bandwidth filter designs often fail to maintain frequency selectivity despite the adjustable bandwidth. In other words, filtering performance deteriorates as the bandwidth increases.

[0006] Existing solutions, such as FSIR-based multi-zero transmission characteristic filters (publication number: CN107732377A), combine multiple FSIRs into an array, thereby creating multipath coupling. By grounding the filter through a hole at the center of the coupling path, electrical coupling is introduced, resulting in electromagnetic hybrid coupling. While a filter based on FSIR has also been disclosed, this approach, by coupling multiple paths and arranging the wavelength FSIRs side by side, requires a large amount of space and makes bandwidth adjustment difficult. Summary of the Invention

[0007] To solve the above problems, the present invention provides a miniaturized microwave filter with a bandwidth-adjustable structure based on BSSIR, which operates in the microwave and millimeter wave frequency bands and can be processed using processes such as PCB, semiconductors, and low-temperature co-fired ceramics. The filter comprises two metal layers and a dielectric layer; the dielectric layer is placed between the two metal layers; the lower metal layer is a ground layer, including a ground metal base plate and a lower metallized through hole, which is arranged at the center of the ground metal base plate; the upper metal layer is a structural layer, specifically comprising: multiple BSSIRs, metal rings, upper metallized through holes, and multiple feed ports; The upper metallized through hole is arranged at the center of the upper metal layer, passes through the upper metal layer, the dielectric layer, and is connected to the lower metallized through hole before being grounded; the metal ring is placed outside the upper metallized through hole, and a concentric circle structure is formed between the two; the multiple BSSIRs are arranged in a centrally symmetrical manner with the metal ring as the axis; the multiple feed ports are arranged at both ends of the BSSIR and are arranged in a centrally symmetrical manner with the metal ring as the axis.

[0008] Furthermore, there are four BSSIRs, each of which is a bell-shaped SIR (BSSIR) in which the low-impedance portion of the SIR structure is concentrated in the middle of the symmetry axis and the high-impedance portions on both sides are brought closer to the low-impedance portion.

[0009] Furthermore, the multiple feed ports are specifically two, each of which consists of an ohmic port and a trapezoidal gradient transition; the two feed ports are respectively connected to the same position of the high-impedance line of one BSSIR and the BSSIR opposite to it, serving as the input and output ports of the filter, and are inverted symmetric around the upper metallized through-hole.

[0010] Furthermore, the impedance of the ohmic port is 50Ω.

[0011] Furthermore, electromagnetic coupling and a transmission zero are introduced into both the lower metallized through hole and the upper metallized through hole.

[0012] Furthermore, the dielectric layer adopts a Roger5880 substrate with a thickness of 0.254 mm, a size of 10.4 mm×10.4 mm, and a guided wavelength of 0.31λg*0.31λg.

[0013] The present invention provides a miniaturized microwave filter with a bandwidth-adjustable structure based on BSSIR, which has the following beneficial effects: The present invention provides a microwave miniaturized filter based on a BSSIR with an adjustable bandwidth structure, which achieves high frequency selectivity, miniaturization, and adjustable filter bandwidth. The present invention achieves electronic bandwidth adjustment by splitting the low-impedance portion of the SIR into several sections and then soldering switched capacitors at the disconnected sections. Bandwidth adjustment is achieved by turning the switching capacitor on and off. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0015] Figure 1 The evolution process from SIR to BSSIR provided by the present invention; Figure 2 A schematic diagram of the structure of an embodiment provided by the present invention; Figure 3 A schematic diagram of the underlying structure of the filter provided by the present invention; Figure 4 A schematic diagram of the upper structure of the filter provided by the present invention; Figure 5 Parameter diagram of the filter provided by the embodiment of the present invention; Figure 6 This is a schematic diagram of the principle of electronic adjustment of the filter bandwidth according to the embodiment of the present invention; Figure 7 This is a schematic diagram of adjustable filter bandwidth parameters according to an embodiment of the present invention.

[0016] In the figure, 1. BSSIR; 2. Metal ring; 3. Lower layer metalized through hole; 4. Trapezoidal gradient transition; 5. Ohmic port; 6. Grounded metal base plate; 7. Upper layer metalized through hole. DETAILED DESCRIPTION

[0017] It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0018] The following describes the implementation method of the present invention in detail with reference to the accompanying drawings. The description only includes some embodiments, not all embodiments. For the purpose of clarity, representations and descriptions that are not related to the present invention are omitted in the drawings and descriptions.

[0019] In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solutions of the present invention are now described in detail below. Obviously, the implementation cases described are part of the embodiments of the present invention, not all of them, and should not be understood as limiting the scope of the implementation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0020] The main purpose of the present invention is to provide a microwave miniaturized filter design technology based on a BSSIR with an adjustable bandwidth structure, which can achieve high frequency selectivity and miniaturization of the filter, and also achieve adjustable filter bandwidth. The first solution for achieving electronic bandwidth adjustment of the filter of the present invention is to cut the low-impedance portion of the SIR into several parts and then weld switching capacitors at the disconnected parts; bandwidth adjustment is achieved by turning the switching capacitors on and off; the second solution is to connect multiple filters of the present invention with different bandwidths in parallel, and connect them with switches in front and behind, to achieve electronic adjustment of different bandwidths in the form of a filter switch matrix.

[0021] The present invention provides a miniaturized microwave filter with a bandwidth-adjustable structure based on BSSIR, which operates in the microwave and millimeter wave frequency bands and can be processed using processes such as PCB, semiconductor, and low-temperature co-fired ceramic (LTCC). The filter comprises two metal layers and a dielectric layer; the dielectric layer is placed between the two metal layers; the lower metal layer is a ground layer, including a ground metal base plate 6 and a lower metalized through hole 3. The lower metalized through hole 3 is arranged at the center of the ground metal base plate 6. Figure 3 As shown; like Figure 4 As shown, the upper metal layer is a structural layer, specifically including: multiple BSSIR1, metal ring 2, upper metallized through hole 7, and multiple feed ports; the upper metallized through hole 7 is arranged at the center of the upper metal layer, passes through the upper metal layer, the dielectric layer and is connected to the lower metallized through hole 3 and then grounded; the metal ring 2 is placed on the outside of the upper metallized through hole 7, and the two are in a concentric circle structure; the multiple BSSIR1 are arranged in a centrally symmetrical manner with the metal ring 2 as the axis; the multiple feed ports are arranged at both ends of the BSSIR1 and are arranged in a centrally symmetrical manner with the metal ring 2 as the axis.

[0022] There are four BSSIR1s. Each BSSIR1 is a bell-shaped SIR with the low impedance part of the SIR structure concentrated in the middle of the symmetry axis and the high impedance parts on both sides close to the low impedance part, as shown in the figure. Figure 1 shown.

[0023] Specifically, there are two feed ports, each consisting of an ohmic port 5 and a trapezoidal gradient transition 4. The two feed ports are connected to the same position on the high-impedance line of one BSSIR1 and the opposite BSSIR1, respectively, serving as the filter's input and output ports, and are inversely symmetrical around the upper metallized through-hole 7. The impedance of the ohmic port 5 is 50Ω.

[0024] Electromagnetic coupling and a transmission zero are introduced into both the lower metallized through hole 3 and the upper metallized through hole 7.

[0025] The dielectric layer uses a Roger5880 substrate with a thickness of 0.254mm, a size of 10.4mm×10.4mm, and a guided wave wavelength of 0.31λg*0.31λg.

[0026] Example: Figure 2 As shown, the operating frequency band is 4.3 GHz. The outer rectangular black frame represents the bottom metal layer. The upper layer contains four BSSIRs, two trapezoidal gradient transitions, two ohmic ports, a metal ring, and a plated through-hole (PTH). The two ohmic ports serve as the filter's input and output ports, each with a 50 ohm impedance, for connection to other circuits. Two trapezoidal gradient transitions are adjacent to the ohmic ports, providing broadband impedance transformation. The four BSSIRs are arranged in a circular pattern around a central symmetrical metal ring. Each adjacent pair can be rotated 90 degrees to overlap. The inner ring of the central metal ring contains a plated through-hole (PTH). An ohmic port and a trapezoidal gradient transition are connected to the same high-impedance line on one BSSIR and the opposite BSSIR, serving as the filter's input and output ports. The two ports are arranged in an anti-symmetric pattern around the central PTH. This circular and anti-symmetric layout of the filter provides multiple coupling paths, forming cross-coupling and introducing a transmission zero in the filter's transfer function. The central plated through-hole introduces electromagnetic coupling and a transmission zero, significantly improving the filter's frequency selectivity. The filter is designed using a 0.254mm thick Roger5880 substrate and measures 10.4mm x 10.4mm. Converted to a guided wavelength of 0.31λg x 0.31λg, the filter's area is reduced by approximately 90%.

[0027] like Figure 5 As shown in the figure, the filter transmission loss is small, about 0.65dB, and there are two transmission zeros near the outer end of the upper sideband, which greatly improves the sideband suppression and stopband suppression.

[0028] like Figure 6 As shown, the low impedance part of the SIR is cut into several parts, and then the switching capacitor is welded at the disconnected part; the bandwidth adjustment is achieved by turning on and off the switching capacitor.

[0029] like Figure 7As shown in the figure, the lower sideband is basically stationary, and the upper sideband extends to high frequency, but the sideband suppression and stopband suppression performance remain basically unchanged.

[0030] The present invention provides a microwave miniaturized filter based on a BSSIR with an adjustable bandwidth structure, which achieves high frequency selectivity, miniaturization, and adjustable filter bandwidth. The present invention achieves electronic bandwidth adjustment by splitting the low-impedance portion of the SIR into several sections and then soldering switched capacitors at the disconnected sections. Bandwidth adjustment is achieved by turning the switching capacitor on and off.

[0031] The foregoing description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein and should not be construed as excluding other embodiments. Rather, the present invention can be used in various other combinations, modifications, and environments and can be modified within the scope of the concept described herein through the above teachings or techniques or knowledge in the relevant field. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention are intended to be protected by the appended claims.

Claims

1. A miniaturized microwave filter with a bandwidth adjustable structure based on BSSIR, comprising two metal layers and a dielectric layer; the dielectric layer is disposed between the two metal layers; the lower metal layer is a grounding layer, comprising a grounding metal base plate (6) and a lower metallized through hole (3); the lower metallized through hole (3) is disposed at the center of the grounding metal base plate (6); and the characteristic is that: The upper metal layer is a structural layer, specifically comprising: a plurality of BSSIRs (1), metal rings (2), upper metallized through holes (7), and a plurality of feed ports; The upper metallized through hole (7) is arranged at the center of the upper metal layer, penetrates the upper metal layer and the dielectric layer, is connected to the lower metallized through hole (3), and is then grounded; the metal ring (2) is placed outside the upper metallized through hole (7), and a concentric circle structure is formed between the two; the multiple BSSIRs (1) are arranged in a centrally symmetrical manner with the metal ring (2) as the axis; the multiple feed ports are arranged at both ends of the BSSIR (1), and are arranged in a centrally symmetrical manner with the metal ring (2) as the axis.

2. The miniaturized microwave filter with a bandwidth adjustable structure based on BSSIR according to claim 1, characterized in that: There are specifically four BSSIRs (1), and each BSSIR (1) is a bell-shaped SIR in which the low-impedance portion of the SIR structure is concentrated in the middle of the symmetry axis and the high-impedance portions on both sides are brought closer to the low-impedance portion.

3. The miniaturized microwave filter with a bandwidth adjustable structure based on BSSIR according to claim 1, characterized in that: The multiple feed ports are specifically two, each of which is composed of an ohmic port (5) and a trapezoidal gradient transition (4); the two feed ports are respectively connected to the same position of the high-impedance line of one BSSIR (1) and the BSSIR (1) opposite to it, serving as the input and output ports of the filter, and are inversely symmetrical around the upper metallized through hole (7).

4. The miniaturized microwave filter with a bandwidth adjustable structure based on BSSIR according to claim 3, characterized in that: The impedance of the ohmic port (5) is 50Ω.

5. The miniaturized microwave filter with a bandwidth adjustable structure based on BSSIR according to claim 1, characterized in that: Electromagnetic coupling and a transmission zero point are introduced into both the lower metallized through hole (3) and the upper metallized through hole (7).

6. The miniaturized microwave filter with a bandwidth adjustable structure based on BSSIR according to claim 1, characterized in that: The dielectric layer adopts a Roger5880 substrate with a thickness of 0.254 mm, a size of 10.4 mm×10.4 mm, and a guided wave wavelength of 0.31λg*0.31λg.

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