Gap waveguide filters based on stub and cavity resonators

Abstract

The application provides a gap waveguide filter based on a stub ring resonator and a cavity resonator, which comprises, from top to bottom, a magnetic field closed structure, a microstrip resonant structure, an artificial magnetic conductor and a cavity resonator which are stacked in sequence; the microstrip resonant structure comprises a stub ring resonator on the upper surface of the second dielectric plate; and the cavity resonator is located at the center position of the artificial magnetic conductor of the periodic structure. The number of transmission zeros of the filter is increased by the stub ring resonator in the microstrip resonant structure and the cavity resonator arranged at the center position of the artificial magnetic conductor, so that the stopband range is widened and the stopband suppression level is strengthened, and the out-of-band selectivity of the gap waveguide filter is effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of microwave technology and relates to a gap waveguide filter, specifically a gap waveguide filter based on a stub ring resonator and cavity resonator structure, which can be used in radio frequency wireless communication systems and other fields. Background Technology

[0002] In communication systems, filters are widely used for channel selection, filtering image frequency interference, attenuating noise, frequency division multiplexing, and in high-performance oscillation, amplification, frequency multiplication, and mixing circuits. They are an indispensable part of radio frequency wireless communication systems. Therefore, research on filters applied in microwave and millimeter-wave bands has significant practical implications.

[0003] In recent years, with the rapid development of communication technology, the demand for wireless systems in the millimeter-wave band has been increasing. Devices designed based on traditional microwave transmission lines face challenges in achieving low loss, high integration, low cost, and high stability. Traditional hollow metal rectangular waveguides have the advantages of low loss and high quality factor, but they are limited by their large size and difficulty in integrating with RF circuits. Although microstrip lines have the advantage of easy integration, in the millimeter-wave band, microstrip lines are prone to radiation loss and surface waves, resulting in reduced transmission efficiency and electromagnetic interference to adjacent circuits. To solve this problem, metal cavities are usually used to shield microstrip circuits. Gap waveguide technology has emerged to address this issue. Gap waveguides have the ability to suppress surface waves and space radiation, making them perfectly suitable for packaged millimeter-wave circuit systems. Gap waveguides can be fabricated using printed circuit boards (PCBs) and possess the advantages of quasi-TEM mode transmission, electromagnetic interference resistance, and surface wave suppression, while also exhibiting excellent integration capabilities.

[0004] For example, in 2021, Tao Xiu et al. published a paper entitled "Design of a Compact and Low-Loss E-Band Filter Based on Multilayer Groove Gap Waveguide" in the IEEE MICROWAVE AND WIRELESS COMPONENTSLETTERS journal, volume 31, no. 11, Nov. 2021. They proposed a multilayer grooved gap waveguide filter, which consists of a metal plate and two artificial magnetic conductors. It forms a resonant cavity by slotting the metal plate of the artificial magnetic conductor in the middle layer. This slotted structure achieves cross-coupling of two transmission paths and generates only two transmission zeros, resulting in low out-of-band selectivity of the gap waveguide filter, which limits the application of gap waveguide filters in the microwave field. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the prior art by proposing a gap waveguide filter based on a stub ring resonator and a cavity resonator, which aims to improve the out-of-band selectivity of the gap waveguide filter.

[0006] To achieve the above objectives, the present invention includes an electromagnetic enclosure structure 1, a microstrip resonant structure 2, and an artificial magnetic conductor 3 stacked sequentially from top to bottom; the electromagnetic enclosure structure 1 includes a first dielectric substrate 11 and a metal plate 12 printed on its upper surface; the electromagnetic enclosure structure 1 and the artificial magnetic conductor 3 can enclose the electromagnetic field generated by the microstrip resonant structure 2 to reduce its loss.

[0007] The microstrip resonant structure 2 includes a stub ring resonator 22 printed on the upper surface of the second dielectric substrate 21, which can be coupled to it, and two stepped impedance microstrip lines 23, as well as two L-shaped microstrip lines 24 printed on its lower surface corresponding to the two stepped impedance microstrip lines. Each stepped impedance microstrip line is connected to its corresponding L-shaped microstrip line through a metallized via 25. The artificial magnetic conductor 3 has a cavity resonator 4 at its center to achieve resonant filtering characteristics.

[0008] In the aforementioned gap waveguide filter, both the second dielectric substrate 21 and the first dielectric substrate 11 are rectangular dielectric substrates.

[0009] The aforementioned gap waveguide filter, wherein the stub ring resonator 22 is located on the line AA' connecting the midpoints of the two long sides of the second dielectric plate 21.

[0010] In the aforementioned gap waveguide filter, the two stepped impedance microstrip lines 23 are located on both sides of the line AA' connecting the midpoints of the two long sides of the second dielectric substrate 21. The two stepped impedance microstrip lines 23 are coupled to the two stubs of the stub ring resonator 22 at the ends of the line AA'.

[0011] In the aforementioned gap waveguide filter, the free ends of the longitudinal arms of the two L-shaped microstrip lines 24 are respectively connected to the ends of the corresponding two stepped impedance microstrip lines near the connecting line AA' through metallized vias 25, and the free ends of the transverse arms of the two L-shaped microstrip lines 24 are coupled.

[0012] The aforementioned gap waveguide filter, wherein the artificial magnetic conductor 3 includes a magnetic conductor dielectric substrate 31, a plurality of first metal patches 32 periodically arranged on the upper surface of the magnetic conductor dielectric substrate 31, and a metal ground plane 33 on the lower surface; a rectangular receiving space is hollowed out at the center of the plurality of first metal patches 32; the metal ground plane 33 is connected to each metal patch through metallized through holes.

[0013] In the aforementioned gap waveguide filter, the first metal patch 32 is rectangular in shape.

[0014] The aforementioned gap waveguide filter, the cavity resonator 4, includes a second metal patch 41 printed on the upper surface of the magnetic conductor dielectric substrate 31. The second metal patch 41 is located in a rectangular accommodating space in the artificial magnetic conductor 3 and is connected to the metal ground plane 33 through a metallized through-hole.

[0015] In the aforementioned gap waveguide filter, the second metal patch 41 is rectangular in shape.

[0016] In the aforementioned gap waveguide filter, the cavity resonator 4 is located at the center of the surface of the magnetic conductor dielectric substrate 31.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] 1. This invention generates two transmission zeros through the self-resonance characteristics of the stub ring resonator, one transmission zero through the mutual coupling of the free ends of the L-shaped microstrip line, and another transmission zero through the cross-coupling of the transmission path of the microstrip resonant structure and the cavity resonator. The total of four transmission zeros generated widens the stopband range and strengthens the stopband suppression level, effectively improving the out-of-band selectivity of the gap waveguide filter.

[0019] 2. The present invention can adjust the position of the transmission zero generated by the filter by adjusting the size of the loaded ring stub resonator, the coupling spacing between the free ends of the L-shaped microstrip line, and the size of the resonant cavity, so that the position of the zero is closer to the passband of the filter, thereby further improving the out-of-band selectivity of the gap waveguide filter. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0021] Figure 2 This is a schematic diagram of the upper surface of the microstrip resonant structure of the present invention;

[0022] Figure 3 This is a schematic diagram of the lower surface of the microstrip resonant structure of the present invention;

[0023] Figure 4 The return loss of the present invention and insertion loss Measured S-parameter graph. Detailed Implementation

[0024] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0025] Reference Figure 1The present invention includes an electromagnetic enclosure structure 1, a microstrip resonant structure 2, and an artificial magnetic conductor 3 stacked sequentially from top to bottom; the electromagnetic enclosure structure 1 includes a first dielectric substrate 11 and a metal plate 12 printed on its upper surface. The electromagnetic enclosure structure 1 and the artificial magnetic conductor 3 can enclose the electromagnetic field generated by the microstrip resonant structure 2 to reduce its loss. The first dielectric substrate is made of Rogers 5880 material with a thickness of 0.3 mm and a dielectric constant of 2.2.

[0026] The microstrip resonant structure 2 has the following structure: Figure 2 and Figure 3 As shown, the filter includes a stub ring resonator 22 printed on the upper surface of a second dielectric substrate 21 and two stepped impedance microstrip lines 23. The stub ring resonator 22 is located on the line AA' connecting the midpoints of the two long sides of the second dielectric substrate 21, and the two stepped impedance microstrip lines 23 are located on both sides of AA'. The second dielectric substrate is made of Rogers 5880 material with a thickness of 0.3 mm and a dielectric constant of 2.2. The microstrip line width W1 of the stub ring resonator is 0.6 mm. By adjusting the width of the stub ring resonator, the operating frequency band of the gap waveguide filter can be adjusted. Simultaneously, a transmission zero is generated on the left and right sides of the passband. The lengths L1 and L2 of the two segments of the stub ring resonator are 11.6 mm and 8 mm, respectively. Adjusting their lengths can adjust the positions of the two transmission zeros. The two stepped impedance microstrip lines are used to match the impedance of the stub ring resonator. The lengths L3 and L4 of the two segments of the stepped impedance microstrip lines are 14.6 mm and 1.8 mm, respectively, and the widths W2 and W3 are respectively... Two L-shaped microstrip lines 24, with lengths of 0.8 mm and 1.2 mm, are printed on the lower surface of the second dielectric substrate, corresponding to the two stepped impedance microstrip lines. These two L-shaped microstrip lines are coupled with a coupling spacing g of 0.1 mm, generating a transmission zero on the right side of the passband. The length of each L-shaped microstrip line is 6.1 mm and the width is 0.3 mm. The position of the transmission zero can be changed by changing the length of the L-shaped microstrip lines and the spacing between them. The top of the longitudinal arm of the L-shaped microstrip line is connected to one end of the line AA' connecting the midpoints of the two long sides of the corresponding stepped impedance microstrip line 23 near the second dielectric substrate 21 through a metallized via 25.

[0027] The artificial magnetic conductor 3 has the following structure: Figure 1 As shown, the device includes a magnetic conductor dielectric substrate 31, a plurality of first metal patches 32 periodically arranged on the upper surface of the magnetic conductor dielectric substrate 31, and a metal ground plane 33 on the lower surface. The magnetic conductor dielectric substrate is made of Rogers 5880 material with a thickness of 2 mm and a dielectric constant of 2.2. The plurality of rectangular patches have a side length of 2 mm, and the spacing between each adjacent metal patch is 0.6 mm. A rectangular receiving space is hollowed out at the center of the plurality of first metal patches 32. The metal ground plane 33 is connected to each metal patch through metallized through holes.

[0028] The artificial magnetic conductor 3 has a cavity resonator 4 at its center. The cavity resonator has a length, width, and height of 9.8 mm, 4.6 mm, and 2 mm, respectively. The cavity resonator 4 includes a second metal patch 41 printed on the upper surface of the magnetic conductor dielectric substrate 31. The second metal patch 41 is located at the center of a rectangular receiving space hollowed out at the center of multiple metal patches. The second metal patch has a length of 1.9 mm and a width of 2 mm. The second metal patch 41 is connected to the metal ground plate 33 through a metallized through-hole.

[0029] The working principle of this invention is as follows: The radio frequency (RF) signal is input from the free end of the stepped impedance microstrip line in the microstrip resonant structure. Through coupling between the stepped impedance microstrip line and a stub ring resonator printed on the upper surface of the first dielectric substrate, the signal is transmitted to the stub ring resonator, exciting it and generating the passband of the filter. Simultaneously, a transmission zero is generated on each side of the passband. The RF signal input from the free end of the stepped impedance microstrip line also reaches the L-shaped microstrip line printed on the lower surface of the first dielectric substrate through a metallized via. Through end coupling of the two L-shaped microstrip lines, a transmission zero is generated on the right side of the passband. During the transmission of the RF signal through the microstrip resonant structure, the microstrip resonant structure couples with a cavity resonator positioned at the center of the artificial magnetic conductor, exciting the cavity resonator. The cross-coupling formed between the two paths of the microstrip resonant structure and the cavity resonator generates a transmission zero on the left side of the passband. The generation of these four zeros effectively improves the out-of-band selectivity of the gap waveguide filter.

[0030] The technical effects of the present invention will be further explained below based on the actual test results:

[0031] 1. Experimental conditions and contents:

[0032] The return loss of this invention was measured using a vector network analyzer N5230C. The insertion loss was measured, and the results are as follows: Figure 4 As shown.

[0033] 2. Analysis of experimental results:

[0034] Reference Figure 4 In this embodiment, the center frequency of the passband is 21.2 GHz; the maximum return loss in the passband... The minimum insertion loss is 35.1 dB. The minimum stopband rejection is 0.45 dB; there are two transmission zeros on the left side of the passband, located at 19.3 GHz and 20.15 GHz respectively; there are two transmission zeros on the right side of the passband, located at 21.9 GHz and 24.95 GHz respectively, resulting in a total of 4 transmission zeros. Within the suppression bandwidth range of 18.65 GHz to 25.7 GHz, the minimum stopband rejection is 17.7 dB; from Figure 4 It can be seen that the four transmission zeros and wide stopband suppression significantly improve out-of-band selectivity.

Claims

1. A gap waveguide filter based on stub and cavity resonators, comprising an electromagnetic closed structure (1), a microstrip resonant structure (2) and an artificial magnetic conductor (3) stacked in order from top to bottom; the electromagnetic closed structure (1) comprises a first dielectric plate (11) and a metal plate (12) printed on the upper surface thereof; the electromagnetic closed structure (1) and the artificial magnetic conductor (3) can close the electromagnetic field generated by the microstrip resonant structure (2) to reduce its loss; characterized in that: the microstrip resonant structure (2) comprises a stub ring resonator (22) printed on the upper surface of a second dielectric plate (21) and two stepped impedance microstrip lines (23) capable of coupling therewith, and two L-shaped microstrip lines (24) printed on the lower surface thereof corresponding to the two stepped impedance microstrip lines, each stepped impedance microstrip line being connected to the corresponding L-shaped microstrip line through a metallized via (25); the artificial magnetic conductor (3) has a cavity resonator (4) arranged at the center thereof for realizing resonant filtering characteristics. The second dielectric plate (21) and the first dielectric plate (11) are both rectangular dielectric plate materials.

2. The gap waveguide filter of claim 1, wherein, The stub ring resonator (22) is located on the line AA' connecting the midpoints of the two long edges of the second dielectric plate (21).

3. The gap waveguide filter of claim 2, wherein, The two stepped impedance microstrip lines (23) are located on both sides of the line AA' connecting the midpoints of the two long edges of the second dielectric plate (21), and the ends of the two stepped impedance microstrip lines (23) close to the line AA' are respectively coupled to the two stubs of the stub ring resonator (22).

4. The gap waveguide filter of claim 2, wherein, The free ends of the longitudinal arms of the two L-shaped microstrip lines (24) are respectively connected to the ends of the corresponding two stepped impedance microstrip lines close to the line AA' through metallized vias (25), and the free ends of the horizontal arms of the two L-shaped microstrip lines (24) are coupled.

5. The gap waveguide filter of claim 2, wherein, The artificial magnetic conductor (3) comprises a magnetic conductor dielectric substrate (31) and a plurality of first metal patches (32) periodically arranged on the upper surface thereof and a metal ground plate (33) on the lower surface thereof; the center of each first metal patch (32) is hollowed out to form a rectangular accommodation space; the metal ground plate (33) is connected to each metal patch through a metallized via.

6. The gap waveguide filter of claim 1, wherein, The first metal patch (32) is rectangular in shape. The cavity resonator (4) comprises a second metal patch (41) printed on the upper surface of the magnetic conductor dielectric substrate (31), which is located in the rectangular accommodation space in the artificial magnetic conductor (3) and is connected to the metal ground plate (33) through a metallized via.

7. The gap waveguide filter of claim 6, wherein, The second metal patch (41) is rectangular in shape.

8. The gap waveguide filter of claim 6, wherein, The cavity resonator (4) is located at the center of the surface of the magnetic conductor dielectric substrate (31).

9. The gap waveguide filter of claim 8, wherein, ​ 10. The gap waveguide filter of claim 9, wherein, ​

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