A zero-adjustable low-loss dual-band filter based on printed ridge gap waveguide

Abstract

The application belongs to the technical field of millimeter wave transmission, and discloses a zero-point adjustable low-loss dual-frequency filter based on a printed ridge gap waveguide, which comprises two waveguide resonant cavities with printed ridge gaps arranged in a center-symmetrical and back-to-back mode along a vertical axis and a shared ground metal plate, the shared ground metal plate is arranged between the two waveguide resonant cavities, a rectangular slot is etched on the shared ground metal plate, the waveguide resonant cavity comprises an upper artificial magnetic conductor layer, a transmission layer and a lower artificial magnetic conductor layer, a resonant column is arranged through the upper and lower artificial magnetic conductor layers and the transmission layer, the resonant column is connected with upper and lower metal ground plates, resonance is generated through the resonant column, a slow wave structure is arranged in the middle of the lower artificial magnetic conductor layer, the transmission layer is connected with a microstrip line, and the microstrip line and the lower artificial magnetic conductor layer are connected through a slow wave through hole. The length and width of the resonator are changed, the electromagnetic mixed coupling mode is adjusted by changing the size and position of the rectangular slot, and the zero-point is adjusted.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of millimeter wave transmission, and particularly relates to a zero-point adjustable low-loss dual-frequency filter based on a printed ridge gap waveguide. BACKGROUND

[0002] The fifth generation mobile communication technology has become a research hotspot, and a communication front-end device with high frequency, good performance and multiple functions has important practical value. The importance of filters in communication systems is increasingly prominent.

[0003] Metal waveguides have the advantages of low loss, large power capacity and no radiation loss, but they also have the disadvantages of large size, difficult processing, difficulty in integration and matching difficulty, and the transmission performance and efficiency need to be further improved. Microstrip lines are an important part of microwave integrated circuits, which are small in size, wide in frequency band and low in cost. However, due to their semi-open structure, the dielectric loss and electromagnetic radiation are greatly increased at high frequencies, which affects the transmission quality of high-frequency signals. Microstrip lines have wide application prospects in various passive device designs, but their shortcomings need to be further optimized and improved in practical applications.

[0004] In modern wireless communication systems, multi-band, high-performance and reconfigurable filters are key components to realize efficient spectrum utilization and system flexibility. Dual-frequency filters can simultaneously process signals of two different frequency bands and are widely used in base stations, satellite communications, multi-mode terminals and other scenarios. Traditional dual-frequency filters are mostly realized by using coupled resonant structures, multi-mode resonators or stepped impedance resonators, but the zero-point position and bandwidth are usually fixed by the structure size and cannot be adjusted after processing.

[0005] In the current common dual-frequency filter, the generation of zero points mostly depends on the cross-coupling or source-load coupling mechanism, and the position is limited by the coupling strength and phase relationship between resonant units. The control of bandwidth is usually realized by adjusting the coupling coefficient between resonators, but in dual-frequency design, the bandwidths of the two passbands often restrict each other and are difficult to independently control. Although some individual researches in the prior art attempt to realize frequency tuning through adjustable capacitors or varactor diodes, it is still difficult to realize independent adjustment of the zero-point position and flexible control of the dual-frequency bandwidth,

[0006] Therefore, how to realize low loss while realizing adjustable dual-frequency band and bandwidth in high-frequency and high-power scenarios has become a technical problem to be solved in the field. SUMMARY

[0007] In order to solve the above technical problems, the application provides a zero-point adjustable low-loss dual-frequency filter based on a printed ridge gap waveguide.

[0008] In order to achieve the above purpose, the application is realized by the following technical scheme:

[0009] The application is a zero-point adjustable low-loss dual-frequency filter based on a printed ridge gap waveguide, which comprises two waveguide resonant cavities with a printed ridge gap arranged in a center-symmetrical and back-to-back manner and a shared ground metal plate, the shared ground metal plate is arranged between the two waveguide resonant cavities, a rectangular slot is etched on the shared ground metal plate, the upper and lower waveguide resonant cavities are electrically and magnetically coupled through the rectangular slot of the shared ground metal plate, the waveguide resonant cavity has a three-layer structure, the first layer is an upper artificial magnetic conductor layer, the second layer is a transmission layer, the transmission medium is air, and the third layer is a lower artificial magnetic conductor layer, one side of the upper artificial magnetic conductor layer and the lower artificial magnetic conductor layer is printed with a metal ground plate, a resonant column is arranged through the upper artificial magnetic conductor layer, the transmission layer and the lower artificial magnetic conductor layer, the resonant column is connected with the upper and lower metal ground plates and generates resonance through the resonant column, a slow wave structure is arranged in the middle of the lower artificial magnetic conductor layer, the transmission layer is connected with a microstrip line, the microstrip line and the lower artificial magnetic conductor layer are connected through a slow wave via, the propagation constant is reduced through the slow wave structure, and low-loss transmission is realized in combination with the field binding characteristics of the ridge gap waveguide.

[0010] Further improvement of the application is that the slow wave structure is a periodically arranged slow wave structure metal column embedded on the lower artificial magnetic conductor layer, a metal via and a metal column are arranged on one side of the slow wave structure on the lower artificial magnetic conductor layer, and the periodically arranged slow wave structure metal column is located in the middle of the metal via and the metal column and the slow wave via, different zero-point frequency filters are realized by changing the arrangement position of the metal via and the metal column.

[0011] Further improvement of the application is that the upper artificial magnetic conductor layer and the lower artificial magnetic conductor layer are arranged in a symmetrical manner and the height of the upper artificial magnetic conductor layer is not equal to the height of the lower artificial magnetic conductor layer.

[0012] The further improvement of the application is that the common ground metal plate is etched with a first rectangular window, a second rectangular window and a third rectangular window, the first rectangular window, the second rectangular window and the third rectangular window are symmetrically arranged along the respective longitudinal center lines, and the first rectangular window and the third rectangular window are symmetrically arranged along the longitudinal center line of the common ground metal plate and are arranged on the two sides of the second rectangular window.

[0013] The further improvement of the application is that the microstrip line comprises a start section connected with the input and output ports, an intermediate section and a tail section connected with the slow wave via, the width of the transmission line section is determined according to the medium plate and air medium respectively, the tail section of the microstrip line is a trapezoidal medium plate, and the intermediate section of the microstrip line is provided with a rectangular air window.

[0014] The beneficial effects of the application are:

[0015] The application has the advantages of ingenious structure, easy processing, low cost and saving of additional packaging.

[0016] The small-sized low-loss transition structure of the printed ridge gap waveguide from the microstrip to the loaded slow wave structure has the advantages that the electromagnetic bandgap structure binds the energy in the propagation layer, especially in a specific frequency band, the electromagnetic field propagation leakage is small, low loss is achieved, and the slow wave structure is introduced, which meets the trend of filter development miniaturization.

[0017] The filter has the characteristics of wide frequency band, low loss and small size in combination with the characteristics of the printed ridge gap waveguide. The introduction of the artificial magnetic conductor can suppress the high-frequency radiation loss, reduce the insertion loss and improve the transmission performance.

[0018] Based on the vertical coupling theory, the filter can change the zero point through the rectangular slot of the window, realize the adjustable zero point, and achieve the low-loss dual-band filter with controllable bandwidth. The radiation loss is suppressed by adopting the artificial magnetic conductor layer, and the conductor and dielectric loss is reduced by optimizing the slow wave structure and the transmission layer design. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of the filter in the embodiment of the application.

[0020] Figure 2 It is a structural schematic diagram of the waveguide resonant cavity in the embodiment of the application.

[0021] Figure 3 It is a structural schematic diagram of the waveguide resonant cavity in the embodiment of the application.

[0022] Figure 4 It is a top view of the structure of the waveguide resonant cavity in the embodiment of the application.

[0023] Figure 5 This is a schematic diagram of the microstrip lines in an embodiment of this application.

[0024] Figure 6 This is a simulation diagram of an embodiment of this application.

[0025] Figure 7 This is a photograph of the fabricated printed ridge gap waveguide microstrip line with a slow-wave structure in an embodiment of this application.

[0026] Figure 8 This is a schematic diagram of the shared ground metal plate in an embodiment of this application.

[0027] Figure 9 The above is a simulation waveform diagram of the adjustable zero-point S-parameter in the embodiments of this application.

[0028] Figure 10 The above is a simulation waveform diagram of the adjustable zero-point S-parameter in the embodiments of this application. Detailed Implementation

[0029] The embodiments of the present invention will be disclosed below with reference to the drawings. For clarity, many practical details will be described in the following description. However, it should be understood that these practical details are not intended to limit the present invention. That is, in some embodiments of the present invention, these practical details are not essential. In addition, for the sake of simplicity, some conventional structures and components will be shown in the drawings in a simple schematic manner.

[0030] like Figure 1 As shown, this application is a zero-point adjustable low-loss dual-frequency filter based on a printed ridge gap waveguide. The zero-point adjustable low-loss dual-frequency filter includes two waveguide resonant cavities with printed ridge gaps arranged back-to-back along the vertical axis and a common ground metal plate 5, which is disposed between the two waveguide resonant cavities.

[0031] like Figures 1-3As shown, the waveguide resonant cavity has a three-layer structure. The first layer is an upper artificial magnetic conductor layer 1, the second layer is a transmission layer 2 (the transmission medium can be air or a dielectric substrate, but air is preferred in this application), and the third layer is a lower artificial magnetic conductor layer 3. The upper artificial magnetic conductor layer 1 and the lower artificial magnetic conductor layer 3 are arranged symmetrically, and the height of the upper artificial magnetic conductor layer 1 is not equal to the height of the lower artificial magnetic conductor layer 3. Metal ground planes are printed on one side of both the upper and lower artificial magnetic conductor layers 1 and 2. Resonant pillars 4 are arranged through the upper and lower artificial magnetic conductor layers 1, 2, and 3, respectively, and are connected to the upper and lower metal ground planes, generating resonance. The transmission layer 2 is connected to a microstrip line, and the microstrip line and the lower artificial magnetic conductor layer 3 are connected by a slow-wave via 6.

[0032] While ensuring the stability of the transmission layer, the thickness g of the transmission layer is ensured to be sufficiently small by precisely controlling the distance between the upper artificial magnetic conductor layer 1 and the lower artificial magnetic conductor layer 3, thereby obtaining a wider electromagnetic bandgap. For example... Figure 2 As shown, in this embodiment, the transmission layer g = 0.127 mm, the lower artificial magnetic conductor layer 3 is 0.127 mm thick, the upper artificial magnetic conductor layer is 0.787 mm thick, and a = 2 mm.

[0033] like Figure 2 As shown, a first rectangular window, a second rectangular window, and a third rectangular window are etched on the common ground metal plate 5. The first rectangular window, the second rectangular window, and the third rectangular window are symmetrically arranged along their respective longitudinal center lines. The first rectangular window and the third rectangular window are symmetrically arranged along the longitudinal center line of the common ground metal plate 5 and are located on both sides of the second rectangular window. The upper and lower waveguide resonant cavities are electrically and magnetically coupled through the rectangular gap of the common ground metal plate 5.

[0034] A slow-wave structure is provided in the middle of the lower artificial magnetic conductor layer 3; for example Figure 3 As shown, the slow wave structure is a periodically arranged slow wave structure metal pillar 8 embedded in the lower artificial magnetic conductor layer 3. A metal through hole and a metal pillar 7 are provided on one side of the slow wave structure on the lower artificial magnetic conductor layer 3, and the periodically arranged slow wave structure metal pillar 8 is located between the metal through hole and the metal pillar 7 and the slow wave through hole 6.

[0035] Resonance is generated by introducing slow-wave vias 6, metal vias, and metal pillars 7 on both sides of the waveguide feed structure. These slow-wave vias and metal vias are connected to the shared ground metal plates above and below, with an overall height of 1.041 mm. At the end of the resonator, a metal via is provided to impede the lateral propagation of electromagnetic waves.

[0036] A top view of the filter after adding metal universal is shown below.Figure 4 As shown, the resonant column 4 is connected with the upper and lower metal ground plate, resonance is generated through the resonant column 4, and the resonance frequency is:

[0037]

[0038] wherein, is the relative dielectric constant, is the relative permeability, is the speed of light, is the length of the resonant structure in the direction, is the resonant column, is the transmission layer thickness, respectively correspond to the resonant mode index in the direction, is the width of the resonant structure in the direction, is the radius of the metal via;

[0039] Neglecting the electromagnetic wave Z-axis separation of the slow wave structure, the expression is simplified as:

[0040]

[0041] The resonant frequency can be changed by adjusting the length and width of the resonator, and the length and width are inversely proportional to the resonant frequency of the resonator, so when the size of the resonator is increased, the resonant frequency will be reduced. Since the width of the slow wave loaded printed ridge gap waveguide transmission transition structure designed in the foregoing is fixed, the value of the length of the resonator can be changed to determine the position of the resonant frequency.

[0042] As shown in Figure 5 , the microstrip line includes a start segment connected with the input and output ports, a middle segment, and a tail segment connected with the slow wave via 6, the width of the transmission line segment is determined according to the dielectric plate and air medium respectively, the tail segment of the microstrip line is a trapezoidal dielectric plate, and the middle segment of the microstrip line is provided with a rectangular air window. The index S of the insertion loss is optimized and improved at 14.21 GHz, which not only reduces the insertion loss at about 14.21 GHz, but also makes the transition matching adjustment more flexible by increasing more variables. The size of the rectangular air window is L2 and W2, the radius of the periodic slow wave structure metal column is R1, the radius of the matching hole is R2, the radius of the slow wave via 6 is R3, and the transverse spacing S1 and the longitudinal spacing S2 of the slow wave structure metal column are 1.25 mm and 1.3 mm.

[0043] The three rows of periodically arranged slow wave structure metal columns 8 on the lower artificial magnetic conductor layer 3 act as a slow wave structure. Since the slow wave effect of the slow wave structure is proportional to the height of the metal column, the height of the upper artificial magnetic conductor layer should be as high as possible, but the height cannot be infinite. If the height is too large, the characteristic impedance of the waveguide will be affected. The transmission layer height g should be as small as possible. Therefore, the waveguide resonant cavity with an asymmetric structure placed face to face in the present application can flexibly adjust the electromagnetic bandgap bandgap range and also make the height design of each layer more flexible. The width of the slow wave structure metal column 8 is W1, which determines the cutoff frequency of the entire printed ridge gap waveguide.

[0044] In order to obtain a cutoff frequency of about 24GHz, the initial width obtained by simulation is 3.4mm. The asymmetric waveguide resonant cavities distributed on both sides have electromagnetic bandgap and co-directional reflection characteristics, and can thus suppress the transverse propagation of electromagnetic waves. According to the electric field and magnetic field distribution, the PRGW electric field loaded with the slow wave structure is concentrated in the transmission layer and the lower artificial magnetic conductor layer. The specific parameters are as follows: L1=6.6mm, L2=1mm, L3=3.7mm, L4=5.15mm, L5=5.95mm, L=18.9mm, W1=3.4mm, W2=0.7mm, W3=0.81mm, W4=0.3mm, W=12.46mm, WP=0.68mm, Wair=0.8mm, R1=0.42mm, R2=0.26mm, S1=1.25mm, S2=1.3mm, R3=0.64mm, wherein L2 is the length of the microstrip line matching the rectangular air window, W2 is the width of the microstrip line matching the rectangular air window, W1 is the width of the slow wave structure metal column 8, S1 is the lateral spacing of the slow wave structure metal column, S2 is the longitudinal spacing of the slow wave structure metal column, R1 is the radius of the periodic slow wave structure metal column, R2 is the radius of the matching hole, R3 is the radius of the slow wave through hole 6, L1 is the length of the slow wave structure, L3 is the length of the middle section of the microstrip line, L4 is the length of the middle section and the tail section of the microstrip line, L5 is the length of the microstrip line, L is the length of the waveguide resonant cavity, W is the width of the waveguide resonant cavity, W3 is the width of the middle section of the microstrip line, W4 is the width of the tail section of the microstrip line, WP is the width of the microstrip line, and Wair is the thickness of the air layer thickness.

[0045] The slow wave structure is loaded in the lower artificial magnetic conductor layer, and the electric field is confined in the upper air. By adjusting the spacing of the slow wave structure metal hole, the magnetic field distribution is not significantly disturbed.

[0046] The present application is simulated and analyzed.

[0047] The 3dB bandwidth of the passband is in the range of 11.61-24.06GHz, and the insertion loss is better than 0.01dB in the range of 13-22GHz, which has a significant advantage at high frequencies. The final optimized insertion loss index S is as follows:Figure 6 As shown. Due to the loading of the slow-wave structure, compared with the printed ridge gap waveguide at the same lateral width, the printed ridge gap waveguide with the loading of the slow-wave structure... Value compared to unloaded The value is reduced by more than 50%. Therefore, at the same cutoff frequency, using a printed ridge gap waveguide loaded with a slow wave can reduce the lateral dimension by more than 50%.

[0048] Figure 7 This image shows a fabricated physical model of a transition structure based on a printed ridge gap waveguide. It comprises three layers: a bottom layer is an artificial magnetic conductor structure with loaded metal vias, a middle layer is a microstrip-fed structure, and a top layer consists of face-to-face artificial magnetic conductor structures. Considering the influence of conductive metal screws on the device, this application uses plastic screws to secure the three-layer structure. Simulation and measurement results are basically consistent. Inner S11 remains the following.

[0049] Based on the electromagnetic field distribution of the single-layer resonator, the final windowing diagram is as follows: Figure 8 As shown. At the second rectangular window, The electric field strength is strongest there, introducing electrical coupling. A rectangular window is etched at the microstrip line, where... The magnetic field strength is the strongest, introducing magnetic coupling. For The mode is one in which electrical coupling and magnetic coupling coexist.

[0050] Electro-coupling and magnetic coupling have different impedance characteristics. The impedance of electro-coupling is a complex, purely imaginary number, often referred to as negative coupling; while the impedance of magnetic coupling is positive, referred to as positive coupling. When an electromagnetic wave signal propagates within a resonant cavity, it is subjected to the combined effects of electro-coupling and magnetic coupling, resulting in a phase superposition on the signal. At a specific frequency or under certain conditions, the phase superposition of electro-coupling and magnetic coupling may reach zero, meaning their phase difference exactly cancels each other out, creating a transmission zero point, effectively suppressing or blocking signal transmission. According to theory:

[0051]

[0052]

[0053] in, Showing the coupling coefficient With negative electrical coupling and positive magnetic coupling The relationship between them The resonant frequency, The cutoff frequency, This relates to the relationship between zero point and resonant point and electromagnetic hybrid coupling. If remain unchanged. increases, the transmission zero point will shift to low frequency. Similarly, if increases, the transmission zero point will appear at high frequency. Thus, in the actual design, the size and position of the rectangular slot can be changed to flexibly adjust and , so as to realize the adjustable zero point, as shown in Figure 9 .

[0054] The simulation results are shown in Figure 10 , and the return loss is less than-25dB in the passband. Through optimization, the final size of the rectangular slot is , . The center frequency of the passband is at 14.63Ghz and 21.55Ghz, respectively, and the 3dB bandwidth of the two passbands is 1.3GHz and 1.8GHz, respectively.

[0055] In summary, in order to reduce the transverse volume, the vertical stacking technology is used, and the electromagnetic coupling is realized by opening the rectangular slot in the middle common ground plane of the upper and lower resonators. The double-band filter of the present application is completed. The 3dB bandwidth of the two passbands of the double-band filter is 1.3GHz and 1.8GHz, respectively, and the zero point is adjustable and the bandwidth is controllable by opening the rectangular slot.

[0056] In summary, the filter designed by the symmetric non-elevated electromagnetic bandgap structure unit combined with the metal column slow wave structure in the present application effectively reduces the physical size without affecting the bandwidth of the electromagnetic bandgap; the proposed transition structure from microstrip to cavity has extremely low insertion loss and bandwidth, and is suitable for microwave device design. The structure of the present application is ingenious, easy to integrate with other circuits, and has a wide application in future millimeter wave communication transmission.

[0057] The above only describes the embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of the claims of the present application.

Claims

1. A zero-adjustable low-loss dual-band filter based on printed ridge gap waveguide, characterized by: The zero adjustable low-loss dual-frequency filter comprises two waveguide resonant cavities which are arranged in a center-symmetrical and back-to-back mode along a vertical axis and a common ground metal plate (5) arranged between the two waveguide resonant cavities, A rectangular slot is etched on the common ground metal plate (5), and the upper and lower waveguide resonant cavities are electrically and magnetically coupled through the rectangular slot of the common ground metal plate (5), The waveguide resonant cavity is a three-layer structure, the first layer is an upper artificial magnetic conductor layer (1), the second layer is a transmission layer (2), the transmission medium is air, and the third layer is a lower artificial magnetic conductor layer (3), one side of the upper artificial magnetic conductor layer (1) and the lower artificial magnetic conductor layer (3) is printed with a metal ground plate, a resonant column (4) is arranged through the upper artificial magnetic conductor layer (1), the transmission layer (2) and the lower artificial magnetic conductor layer (3), the resonant column (4) is connected with the upper and lower metal ground plates, and resonance is generated through the resonant column (4); A slow wave structure is arranged in the middle of the lower artificial magnetic conductor layer (3); The transmission layer (2) is connected with a microstrip line, the microstrip line and the lower artificial magnetic conductor layer (3) are connected through a slow wave via hole (6), the propagation constant is reduced through the slow wave structure, the field confinement of the ridge gap waveguide is combined, and low-loss transmission is realized, wherein, The slow wave structure is a periodically arranged slow wave structure metal column (8) embedded on the lower artificial magnetic conductor layer (3), a metal via hole and a metal column (7) are arranged on the lower artificial magnetic conductor layer (3) on one side of the slow wave structure, and the periodically arranged slow wave structure metal column (8) is located in the middle of the metal via hole and the metal column (7) and the slow wave via hole (6), different zero frequency filtering is realized by changing the arrangement position of the metal via hole and the metal column (7); A first rectangular window, a second rectangular window and a third rectangular window are etched on the common ground metal plate (5), the first rectangular window, the second rectangular window and the third rectangular window are respectively arranged symmetrically along respective longitudinal center lines, and the first rectangular window and the third rectangular window are arranged symmetrically along the longitudinal center line of the common ground metal plate (5) and are arranged on both sides of the second rectangular window; The microstrip line comprises a start segment connected with an input / output port, a middle segment and a tail segment connected with the slow wave via hole (6), the tail segment of the microstrip line is a trapezoidal dielectric plate, and the middle segment of the microstrip line is provided with a rectangular empty window.

2. The zero-adjustable low-loss dual-band filter based on printed ridge gap waveguide according to claim 1, characterized in that: The upper artificial magnetic conductor layer (1) and the lower artificial magnetic conductor layer (3) are arranged in a symmetrical mode, and the height of the upper artificial magnetic conductor layer (1) is not equal to the height of the lower artificial magnetic conductor layer (3).

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