Band-pass filter

Abstract

The invention discloses a band-pass filter, and relates to the technical field of filters, the band-pass filter comprises an upper metal layer, a dielectric substrate and a lower metal layer, the dielectric substrate is clamped by the upper metal layer and the lower metal layer to form a single-layer substrate integrated waveguide cavity structure, the upper metal layer, the dielectric substrate and the lower metal layer are respectively provided with a plurality of through holes which are opposite to each other to form two 1 / 4 mode substrate integrated waveguide resonant cavities, and the through holes which share the same edge of the two 1 / 4 mode substrate integrated waveguide resonant cavities serve as coupling windows of the two 1 / 4 mode substrate integrated waveguide resonant cavities. Two adjacent micro-strip resonators are arranged at the tops of coupling windows of the two 1 / 4 mode substrate integrated waveguide resonant cavities of the upper metal layer, and the two 1 / 4 mode substrate integrated waveguide resonant cavities and the two micro-strip resonators jointly achieve four-order filter response but only occupy the circuit area of the two 1 / 4 mode substrate integrated waveguide resonant cavities. The band-pass filter is small in size, simple in structure and wide in passband.

Description

Technical Field

[0001] The present invention relates to the technical field of filters, and in particular to a bandpass filter. Background Art

[0002] Generally, filters play a key role in communication systems. By selectively transmitting or suppressing the frequency components of signals, they achieve spectrum shaping, noise suppression and distortion reduction of signals, thereby improving the transmission quality and reliability of communication systems. Substrate Integrated Waveguide (SIW) has the advantages of low loss, high quality factor, low cost and easy integration, and is widely used in the design of various filters. However, compared with microstrip filters, the circuit size of SIW filters is still large. At the same time, because SIW has similar mode characteristics to waveguides, its high-order modes are densely distributed, and the harmonics generated are often close to the passband.

[0003] In the prior art, some researchers have proposed a band-pass filter (BPF) that is realized by mixing a SIW resonant cavity with a microstrip resonator, which can overcome the above two shortcomings of the SIW filter to a certain extent. The band-pass filter achieves good performance, including steep skirts and low losses. However, the size of the band-pass filter is relatively large. There are also studies that combine two substrate integrated waveguide cavities and two folded quarter-wavelength microstrip line resonators to propose a single-layer band-pass filter that can achieve a fourth-order filtering response. But again, it uses a complete SIW resonant cavity, resulting in insufficient miniaturization. There are also studies that have realized a band-pass filter with wide stopband characteristics by etching two microstrip-based uniform impedance resonators (UIRs) between two SIW cavities. The staggered high-order mode frequencies of the UIRs and SIW cavities help suppress the harmonics of the two resonant structures. However, the filter still has the problem of large circuit size. Another study proposed a new type of filter with high selectivity, which uses a hybrid multilayer half-mode substrate integrated waveguide (Half-Mode Substrate Integrated Waveguide, HMSIW). Although the circuit size of the filter is reduced, the structure of the filter is more complicated, and the double-layer structure brings about the problem of increased volume of the filter. These disadvantages will limit the application of the filter. Another study proposed a miniaturized multilayer quarter-mode substrate integrated waveguide (Quarter-Mode Substrate Integrated Waveguide, QMSIW) filter with high selectivity and wide stopband. The use of QMSIW greatly reduces the circuit size of the filter, but the double-layer structure still makes its structure complicated and increases the difficulty of processing.

[0004] In summary, the current traditional bandpass filters have the problems of large size and complex structure, which limits the application occasions of the bandpass filters. Summary of the invention

[0005] Based on this, it is necessary to provide a bandpass filter to address the above technical issues.

[0006] The present invention adopts the following technical solutions:

[0007] The present invention provides a bandpass filter, comprising: an upper metal layer, a dielectric substrate and a lower metal layer; the upper metal layer and the lower metal layer sandwich the dielectric substrate to form a single-layer substrate integrated waveguide cavity structure;

[0008] A plurality of through holes facing each other are provided on the upper metal layer, the dielectric substrate and the lower metal layer to form two 1 / 4 mode substrate integrated waveguide resonant cavities; the through holes on the common sides of the two 1 / 4 mode substrate integrated waveguide resonant cavities are used as coupling windows of the two 1 / 4 mode substrate integrated waveguide resonant cavities;

[0009] Coplanar waveguide transmission lines are respectively provided on both sides of the two 1 / 4 mode substrate integrated waveguide resonant cavities in the upper metal layer as excitation ports;

[0010] Two adjacent microstrip resonators are arranged on the top of the coupling windows of the two 1 / 4 mode substrate integrated waveguide resonant cavities on the upper metal layer, the two microstrip resonators are symmetrically arranged based on the coupling windows of the two 1 / 4 mode substrate integrated waveguide resonant cavities, and the short-circuit ends of the two microstrip resonators are adjacent;

[0011] A pair of through holes are provided on both sides of the coupling windows of the two 1 / 4 mode substrate integrated waveguide resonant cavities on the upper metal layer, the dielectric substrate and the lower metal layer, serving as coupling windows between the two 1 / 4 mode substrate integrated waveguide resonant cavities and the two microstrip resonators.

[0012] Optionally, the two 1 / 4 mode substrate integrated waveguide resonant cavities operate in TE0.5 / 0.5 / 0 mode; there is magnetic coupling between the two 1 / 4 mode substrate integrated waveguide resonant cavities and the two microstrip resonators, there is magnetic coupling between the two microstrip resonators, and there is electrical coupling between the two 1 / 4 mode substrate integrated waveguide resonant cavities.

[0013] Optionally, the dielectric substrate is a dielectric substrate made of ZYF300CA-P; the dielectric substrate has a relative dielectric constant of 3, a loss tangent of 0.0018 and a thickness of 0.762 mm.

[0014] Optionally, the coplanar waveguide transmission line serving as an excitation port is a 50-ohm coplanar waveguide transmission line.

[0015] Optionally, one of the two microstrip resonators is in the form of a 2-type pen-segment without a bottom edge, and the other is in the form of a 5-type pen-segment without a bottom edge.

[0016] At least one of the above technical solutions adopted by the present invention can achieve the following beneficial effects:

[0017] The bandpass filter of the present invention adopts a single-layer substrate integrated waveguide cavity structure, adopts two QMSIW resonant cavities, and embeds two microstrip resonators on the top of the coupling window between the QMSIW resonant cavities. The two QMSIW resonant cavities and the two microstrip resonators jointly realize the fourth-order filter response, but only occupy the circuit area of ​​the two QMSIW resonant cavities. The bandpass filter of the present invention has a small size, a simple structure and a wide passband, which ensures the high selectivity of the filter and improves the applicability to various application occasions. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0019] Figure 1 A schematic diagram of a bandpass filter provided by the present invention;

[0020] Figure 2 A schematic diagram of the dimensions of an upper metal layer provided by the present invention;

[0021] Figure 3 A schematic diagram of a coupling topology structure of a bandpass filter provided by the present invention;

[0022] Figure 4 A simulation model and a transfer response schematic diagram provided by the present invention;

[0023] Figure 5 A schematic diagram of a resonant mode of a bandpass filter provided by the present invention;

[0024] Figure 6 A schematic diagram of the electric field distribution of a main mode TE0.5 / 0.5 / 0 mode and two higher-order modes TE1.5 / 0.5 / 0 and TE0.5 / 1.5 / 0 closest to the passband in a bandpass filter provided by the present invention;

[0025] Figure 7 A schematic diagram of a bandpass filter and its S parameters provided by the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.

[0027] At present, the research on filter design for miniaturized hybrid structures is still in its infancy, and further exploration in this area will also have important scientific significance and practical value.

[0028] Therefore, the present invention proposes a hybrid structure BPF based on QMSIW and microstrip resonator. First, the use of QMSIW can effectively reduce the size of the filter, and the high-order modes TE120, TE210 and TE220 cannot propagate in the resonant cavity, which can effectively increase the stopband width of the filter. Secondly, two microstrip resonators are embedded at the top position of the coupling window, and the fourth-order filtering response is achieved with only the circuit area of ​​two QMSIW resonant cavities. At the same time, by introducing cross-coupling, two transmission zeros (TransmissionZeros, TZs) are generated, ensuring the high selectivity of the filter. Finally, the filter is a single-layer substrate integrated waveguide cavity structure, which is simple to manufacture and easy to integrate into the communication system.

[0029] The technical solutions provided by various embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0030] Figure 1 is a schematic diagram of a bandpass filter in the present invention, comprising Figure 1 It can be seen that in one or more embodiments of the present invention, the bandpass filter may include: an upper metal layer 100, a dielectric substrate 200 and a lower metal layer 300, wherein the upper metal layer 100 and the lower metal layer 300 sandwich the dielectric substrate 200 to form a single-layer substrate integrated waveguide cavity structure. A plurality of through holes facing each other are provided on the upper metal layer 100, the dielectric substrate 200 and the lower metal layer 300 to form two 1 / 4 mode substrate integrated waveguide resonant cavities (cavity 1 and cavity 2), and the through holes on the common sides of the two 1 / 4 mode substrate integrated waveguide resonant cavities are used as coupling windows of the two 1 / 4 mode substrate integrated waveguide resonant cavities. Coplanar waveguide transmission lines are provided on both sides of the two 1 / 4 mode substrate integrated waveguide resonant cavities of the upper metal layer 100 as excitation ports 101 / 102. Two adjacent microstrip resonators 103 are arranged on the top of the coupling windows of the two 1 / 4 mode substrate integrated waveguide resonant cavities on the upper metal layer 100. The two microstrip resonators 103 are symmetrically arranged based on the coupling windows of the two 1 / 4 mode substrate integrated waveguide resonant cavities, and the short-circuit ends of the two microstrip resonators 103 are adjacent.

[0031] A pair of through holes are provided on both sides of the coupling windows of the two 1 / 4 mode substrate integrated waveguide resonant cavities on the upper metal layer 100 , the dielectric substrate 200 and the lower metal layer 300 , serving as coupling windows between the two 1 / 4 mode substrate integrated waveguide resonant cavities and the two microstrip resonators 103 .

[0032] There is magnetic coupling between the two 1 / 4 mode substrate integrated waveguide resonant cavities and the two microstrip resonators 103 , there is magnetic coupling between the two microstrip resonators 103 , and there is electrical coupling between the two 1 / 4 mode substrate integrated waveguide resonant cavities.

[0033] As can be seen from the above, the present invention adopts a single-layer substrate integrated waveguide cavity structure. Specifically, in one or more embodiments of the present invention, for the dielectric substrate 200, it can be a dielectric substrate made of ZYF300CA-P, whose relative dielectric constant is 3, loss tangent is 0.0018 and thickness can be 0.762mm.

[0034] The bandpass filter of the present invention is generally two QMSIW resonant cavities and operates in TE0.5 / 0.5 / 0 mode. A coupling window is set at the common edge of the two QMSIW resonant cavities, and two microstrip resonators 103 are embedded at the top position of the coupling window. The microstrip resonator 103 can be equivalent to a quarter-wavelength short-circuit resonator. A pair of metal through holes are set on the lower side of the microstrip resonator 103, and the two symmetrically arranged through holes are respectively located below the two microstrip resonators 103.

[0035] Figure 2 The coupling between the QMSIW resonant cavity and the microstrip resonator can be adjusted by adjusting the size W3. The coupling between the two microstrip resonators 103 can be adjusted by adjusting the spacing g between them. 1 The excitation ports 101 / 102 both use 50 ohm coplanar waveguide transmission lines to achieve energy coupling between the source / load and the filter.

[0036] Figure 3 The figure is a schematic diagram of the coupling topology structure of a bandpass filter in the present invention, in which the coupling between the QMSIW resonant cavity and the microstrip resonator is magnetic coupling. The short-circuited ends of the two microstrip resonators are close to each other, so that they are also magnetically coupled. There is a relatively weak electrical coupling between the two QMSIW resonant cavities, which is because part of the electric field can be coupled through the opening edge of the cavity. It is the electrical coupling between the QMSIW resonant cavities that realizes cross-coupling, so that transmission zeros can be generated on both sides of the passband of the filter, thereby improving the selectivity of the filter.

[0037] for Figure 2The 1 / 4 mode substrate integrated waveguide (QMSIW) resonant cavity can be regarded as a complete SIW cavity, which is cut twice along the symmetry plane of the SIW cavity, and its size is 1 / 4 of the SIW cavity. The resonant frequency of the main mode TE0.5 / 0.5 / 0 of the QMSIW resonant cavity is determined by the TE110 mode of the SIW cavity. The resonant frequency of the TE110 mode of the SIW cavity is determined by the following formula:

[0038]

[0039] In the formula, c 0 is the speed of light in a vacuum, ε r is the relative dielectric constant of the dielectric substrate, W eff-SIW is the equivalent width of the SIW cavity, L eff-SIW is the equivalent length of the SIW cavity, which is defined as follows:

[0040]

[0041] Where W SIW and L SIW represents the width and length of the SIW cavity, d is the diameter of the circular hole, and p is the center distance between adjacent circular holes. In one or more embodiments of the present invention, WSIW=2W, LSIW=2L.

[0042] Since the microstrip resonator can be equivalent to a quarter-wavelength short-circuit resonator, its input admittance can be expressed as Y in =-jY 0 cotθ 0 When Y in When it is equal to zero, the calculation formula of its resonant frequency can be expressed as:

[0043]

[0044] In the formula, ε e is the equivalent dielectric constant of the microstrip resonator. R is the length of the resonator. i=0,1,2,…, when i=0, it indicates the main resonance mode, and when i>0, it indicates the higher-order resonance mode.

[0045] Therefore, once the design frequency of the filter is determined, the dimensions of the QMSIW resonant cavity and the microstrip resonator can be initially designed. In one or more embodiments of the present invention, L = 12.6, P = 1.8, d = 1, W = 11.7, W1 = 1.88, L1 = 4.25, m = 6.5, g = 1.2, d1 = 0.6, W2 = 6.5, W3 = 4.5, g1 = 0.34, s = 0.37, all in mm.

[0046] The specifications and design curves of the bandpass filter in the present invention are described by taking a fourth-order quasi-elliptical response with a center frequency of 4.12 GHz, a return loss of 21 db, and a relative bandwidth of 32.7% as an example. The coupling coefficient and external quality factor of the bandpass filter are:

[0047] K 12 =K 34 =0.3,K 23 =0.24,K 14 =-0.023,Q e =2.76.

[0048] In the formula, K ij represents the microstrip resonator R i and R j The coupling coefficient between e is the external quality factor. According to the expected target specification, Figure 4 The main coupling coefficient (i.e., K) in the case of external weak coupling can be extracted 12 and K 34 , K 23 ), the corresponding simulation model and transfer response are as follows Figure 4 As shown. Figure 4 (a) It can be seen that as W 3 The increase of K 12 and K 34 This is because as W 3 As the gap (i.e. g1) increases from 0.2mm to 0.5mm, K 23 It changes from 0.411 to 0.154, showing a downward trend. The cross-coupling coefficient K is extracted through eigensimulation simulation 14 ,like Figure 4 As shown in (c), K 14 Mainly affected by the dimension g 1 Control, with g 1 The increase of K 14 It increases from 0.0230 to 0.0238. These extracted curves have certain guiding significance for filter design, but there may be certain numerical deviations compared with the synthetic parameters.

[0049] In addition, due to the high aspect ratio of SIW (usually greater than 10), when the SIW cavity is cut along the symmetry plane, the energy is mainly confined to the semi-open dielectric filling area surrounded by the metal through-hole array and the upper and lower metal planes for propagation. The open side can be regarded as an ideal magnetic wall, so the main mode electric field distribution of the QMSIW resonant cavity will be basically unaffected, that is, only 1 / 4 of the electric field of the SIW cavity is retained. Similarly, for the high-order modes of the QMSIW resonant cavity, they can only propagate in the QMSIW resonant cavity if the symmetry plane is equivalent to a magnetic wall. Figure 5 (a) The first five resonant modes of the SIW cavity. Figure 5 (b) shows the first two resonant modes of the QMSIW resonant cavity. It can be seen that by utilizing the structural characteristics of the QMSIW alone, it is possible to suppress the high-order modes that cannot be equivalent to magnetic walls at the symmetry planes such as TE120, TE210, and TE220.

[0050] Figure 6 The figure is a schematic diagram of the electric field distribution of the main mode TE0.5 / 0.5 / 0 mode and the two higher-order modes TE1.5 / 0.5 / 0 and TE0.5 / 1.5 / 0 closest to the passband in a bandpass filter in the present invention. It can be seen that the main mode TE0.5 / 0.5 / 0 mode can propagate normally in the filter. Both the higher-order modes TE1.5 / 0.5 / 0 and TE0.5 / 1.5 / 0 will split into a pair of odd and even modes, which will generate a certain output in the filter to form a parasitic passband. No parasitic passbands generated by the modes corresponding to the higher-order modes TE120, TE210, and TE220 of the SIW cavity are found in the filter, which proves the correctness of the above inference.

[0051] In order to verify the performance of the bandpass filter proposed above, the bandpass filter was processed using PCB technology. Figure 7 (a) is a physical picture of the processed bandpass filter, and its physical size is 25.2×11.7mm2 (excluding input and output ports). When testing the filter, it is necessary to weld SMA-KHD coaxial connectors at the input and output ports of the filter and connect them to the Agilent E8363C network vector analyzer for measurement. Figure 7 (b) depicts the simulated, measured, and synthesized S-parameters, which are performed over the frequency range of 2 to 14 GHz and good agreement is observed. The center frequency is measured to be 4.1 GHz, which is slightly less than the simulated value. The measured 3 dB fractional bandwidth (FBW) is 39.47% and the minimum insertion loss (including the loss of the SMA connector) is 0.9 dB. At the same time, the stopband is above 8.25 GHz with a suppression level greater than 20 dB. As expected, two transmission zeros are observed on both sides of the passband. The measured insertion loss is 0.5 dB higher than the simulated value, and the return loss is better than 19 dB (2 dB lower than the simulated value). The difference between the measured and simulated results is mainly attributed to processing errors, dielectric losses, and conversion structure losses.

[0052] Compared with the existing bandpass filters, the bandpass filter of the present invention shows wider relative bandwidth, lower insertion loss, better return loss, and smaller size. In addition, the filter is only a single-layer structure, which is simple to manufacture, easy to implement, and easier to integrate into the communication system.

[0053] It should also be noted that the terms “comprises”, “includes” or any other variations thereof in the present invention are intended to cover non-exclusive inclusion, that is, in addition to the elements listed in the present invention, other elements not explicitly listed may also be included.

[0054] The various embodiments of the present invention are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments.

[0055] The above description is only an embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A bandpass filter, characterized in that: include: An upper metal layer, a dielectric substrate and a lower metal layer; the upper metal layer and the lower metal layer sandwich the dielectric substrate to form a single-layer substrate integrated waveguide cavity structure; A plurality of through holes facing each other are provided on the upper metal layer, the dielectric substrate and the lower metal layer to form two 1 / 4 mode substrate integrated waveguide resonant cavities; the through holes on the common sides of the two 1 / 4 mode substrate integrated waveguide resonant cavities are used as coupling windows of the two 1 / 4 mode substrate integrated waveguide resonant cavities; Coplanar waveguide transmission lines are respectively arranged on both sides of the two 1 / 4 mode substrate integrated waveguide resonant cavities in the upper metal layer as excitation ports; Two adjacent microstrip resonators are arranged on the top of the coupling windows of the two 1 / 4 mode substrate integrated waveguide resonant cavities on the upper metal layer, the two microstrip resonators are symmetrically arranged based on the coupling windows of the two 1 / 4 mode substrate integrated waveguide resonant cavities, and the short-circuit ends of the two microstrip resonators are adjacent; A pair of through holes are provided on both sides of the coupling windows of the two 1 / 4 mode substrate integrated waveguide resonant cavities on the upper metal layer, the dielectric substrate and the lower metal layer, serving as coupling windows between the two 1 / 4 mode substrate integrated waveguide resonant cavities and the two microstrip resonators.

2. The bandpass filter according to claim 1, characterized in that The two 1 / 4 mode substrate integrated waveguide resonant cavities operate in TE0.5 / 0.5 / 0 mode; there is magnetic coupling between the two 1 / 4 mode substrate integrated waveguide resonant cavities and the two microstrip resonators, there is magnetic coupling between the two microstrip resonators, and there is electrical coupling between the two 1 / 4 mode substrate integrated waveguide resonant cavities.

3. The bandpass filter according to claim 1, wherein: The dielectric substrate is a dielectric substrate made of ZYF300CA-P; the dielectric substrate has a relative dielectric constant of 3, a loss tangent of 0.0018 and a thickness of 0.762 mm.

4. The bandpass filter according to claim 1, wherein: The coplanar waveguide transmission line used as the excitation port is a 50-ohm coplanar waveguide transmission line.

5. The bandpass filter according to claim 1, wherein: One of the two microstrip resonators is in the form of a 2-type pen-segment without a bottom edge, and the other is in the form of a 5-type pen-segment without a bottom edge.

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