A reconfigurable differential filter based on hmcsiw

Abstract

The application belongs to the field of microwave technology and discloses a reconfigurable differential filter based on HMCSIW, which comprises a first layer metal layer, a first layer dielectric layer, a second layer metal layer, a second layer dielectric layer and a third layer metal layer, the first layer metal layer is composed of a rectangular patch of a half-mode combline, a pair of trapezoidal microstrip lines, a pair of open-circuit microstrip stubs and a DBCSRR structure, the second layer metal layer is composed of a rectangular slot and a folded SSPPs structure and is a common ground of the structure, and the third layer metal layer is completely consistent with the structure size of the first layer metal layer. The length of the open-circuit stubs connected in parallel on the HMCSIW is controlled by the conduction and shutdown of the PIN diode, so that the resonant frequency of the open-circuit stubs is controlled, then the low-frequency zero point of the filter will change, and the bandwidth and center frequency of the entire filter will change accordingly. The filter can be reconfigured and combined with the differential transmission line, and has a common-mode rejection characteristic.

Description

Technical Field

[0001] This invention belongs to the field of microwave technology, specifically relating to a reconfigurable differential filter based on HMCSIW. Background Technology

[0002] Substrate integrated waveguide (SIW) technology has attracted considerable attention due to its low cost and planar design, and SIW-based integrated circuits are widely used in wireless communication systems. However, the presence of metal vias necessitates complex biasing circuits when active devices are integrated onto the SIW. Comb-like substrate integrated waveguides (CSIW) use a set of quarter-wavelength microstrip open stubs to replace the metal vias in the SIW, forming equivalent electric walls to confine electromagnetic waves within the waveguide. Since the top and bottom metal layers in a CSIW are independent, it facilitates integration with active devices. To further meet the demands of miniaturization, the size of the CSIW circuit is halved, forming a half-mode comb-like substrate integrated waveguide (HMCSIW). Its longitudinal open edge can be directly integrated with active devices, enabling reconfigurable microwave devices.

[0003] Differential transmission lines are widely used in modern wireless communication systems due to their high immunity to environmental noise. The literature "Deng HW, Zhu JM, Sun L, et al. Design of compact multilayer differential CSIW and HMCSIW with high common-mode suppression[J].IEEE Microwave and Wireless Components Letters,2020,30(6):549-552" proposes CSIW differential transmission lines and HMCSIW differential transmission lines with high common-mode suppression.

[0004] Previous research on HMCSIW-based filters has largely failed to combine reconfigurability with common-mode rejection. Therefore, research on HMCSIW-based reconfigurable differential filters is of great significance. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a reconfigurable differential filter based on HMCSIW. This is achieved by connecting a quarter-wavelength open-circuit microstrip stub in parallel on the open edges of the upper and lower HMCSIWs, disconnecting the stub at an appropriate position, and then connecting it again with a PIN diode. By controlling the switching on and off of the diode, the length of the open-circuit stub connected in parallel to the HMCSIW is changed, thereby altering its resonant frequency and causing a change in the frequency of the filter's low-frequency zero.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] This invention relates to a reconfigurable differential filter based on HMCSIW. The reconfigurable differential filter comprises, from top to bottom, a first metal layer, a first dielectric substrate, a second metal layer, another second dielectric substrate, and a third metal layer. The lower surface of the first dielectric substrate and the upper surface of the second dielectric substrate constitute the second metal layer, which is the common ground plane of this structure. The lower surface of the second dielectric layer constitutes the third metal layer, and the structure of the third metal layer is identical to that of the first metal layer. The first metal layer is disposed on the upper surface of the first dielectric substrate and includes an HMCSIW rectangular patch, a trapezoidal microstrip line, and a pair of L-shaped quad... The filter employs a half-wavelength open-circuit stub and a DBCSRR structure. Several comb-like open-circuit stubs and L-shaped quarter-wavelength open-circuit stubs are arranged on a rectangular HMCSIW patch. The L-shaped quarter-wavelength open-circuit stubs are connected in parallel with the rectangular HMCSIW patch and positioned near both edges. Each L-shaped quarter-wavelength open-circuit stub is disconnected and connected with a PIN diode. The length of the L-shaped quarter-wavelength open-circuit stub is controlled by turning the PIN diode on and off, thereby changing its resonant frequency. This alters the low-frequency zero point of the filter, and consequently, the bandwidth and center frequency of the entire filter change accordingly.

[0008] A further improvement of the present invention is that the width of the HMCSIW rectangular patch is determined according to the operating frequency of the filter, specifically:

[0009]

[0010]

[0011] Among them: W eff W is the equivalent width of the rectangular patch. SIW d is the actual width of the rectangular patch, s is the width of the comb-like microstrip stub, h is the spacing between two adjacent microstrip stubs, and the operating frequency band is TE. 10 Cutoff frequency to TE in mode 20 Cutoff frequency in the mode.

[0012] A further improvement of the present invention is that: a rectangular slit is etched on the second metal layer, and a folded SSPPs structure is provided at equal intervals at one end of the rectangular slit (6). The width of the rectangular slit is related to the strength of common mode suppression. The wider the rectangular slit, the stronger the common mode suppression. The length of the folded SSPPs structure is determined according to the frequency range of common mode suppression. The longer the folded SSPPs structure, the lower the frequency range of common mode suppression.

[0013] A further improvement of the present invention is that the length of the L-shaped quarter-wavelength open-circuit stub on the first metal layer and the third metal layer is determined according to the frequency of the low-frequency zero point. The longer the length of the L-shaped quarter-wavelength open-circuit stub, the lower the frequency of the low-frequency zero point.

[0014] A further improvement of the present invention is that: the closer the L-type quarter-wavelength open-circuit stub is to the central axis, the smaller the change in the low-frequency zero point when the PIN diode is turned on and off, and the pole generated by the L-type quarter-wavelength open-circuit stub moves towards the low frequency.

[0015] A further improvement of the present invention is that the DBCSRR structure on the first and third metal layers is placed in the center position, so that the entire filter structure is symmetrical from left to right. The size of the DBCSRR structure is determined according to the frequency of the high-frequency zero point. The larger the size of the DBCSRR structure, the lower the frequency of the high-frequency zero point.

[0016] A further improvement of the present invention is that the DBCSRR structure includes an inner ring and an outer ring, both of which are provided with openings, and the openings of the inner ring and the outer ring do not correspond to each other.

[0017] A further improvement of the present invention is that: there are ports and microstrip lines on both sides of the trapezoidal microstrip line, and the impedance of each is 50Ω.

[0018] The working principle of this invention is as follows: Several quarter-wavelength open-circuit stubs replace metal vias, forming electric walls between the first and second metal layers and between the third and second metal layers, respectively, confining the electromagnetic field and forming two SIW resonant cavities. The HMCSIW is half the size of the CSIW, with one open edge for direct loading of active devices. A pair of open-circuit microstrip stubs are connected in parallel on the open edges of the first and third HMCSIW layers to generate a low-frequency zero. A DBCSRR structure is etched on the HMCSIW metal layer to generate a high-frequency zero. PIN diodes are loaded at the same positions on the two pairs of open-circuit stubs. By controlling the on / off state of the PIN diodes, the length of the parallel open-circuit stubs is controlled, thereby changing the frequency of the low-frequency zero. A rectangular slot is etched on the second metal layer, and an SSPPs structure is loaded on the side near the open edge of the HMCSIW to achieve common-mode rejection. The filter is fed through a trapezoidal microstrip line to achieve impedance matching. The four PIN diodes are simultaneously turned off and on, giving the filter a low-frequency zero with two states. This filter achieves good return loss and insertion loss in both operating states. The isolation coefficient and reflection coefficient are both below -15dB in the low-frequency zero states of 10.05GHz and 11.15GHz, and the common-mode rejection is greater than 40dB in both states. The high-frequency zero is 14GHz in both states. Compared with other types of reconfigurable filters, this invention exhibits good performance in terms of isolation and reflection coefficient in the operating frequency range.

[0019] The beneficial effects of this invention are:

[0020] (1) The present invention changes the frequency of the low-frequency zero point by controlling the on and off of the PIN diode and changing the length of the parallel microstrip stub.

[0021] (2) The present invention generates a stopband by etching a DBCSRR structure on the first and third HMCSIW metal layers, which serves as the high-frequency zero of the filter.

[0022] (3) Based on the HMCSIW differential transmission line, this invention proposes a novel reconfigurable filter that can move the low-frequency zero without changing the filter size, thereby achieving reconfigurable bandwidth and center frequency.

[0023] (4) The present invention ultimately enables the reconfigurable differential filter based on HMCSIW to maintain good filtering performance while also having common mode suppression characteristics.

[0024] (5) Without changing the structural dimensions, the present invention achieves the low-frequency zero-point reconfigurable performance of the filter based on the half-mode comb-line substrate integrated waveguide, while maintaining good working performance of the filter in both states.

[0025] (6) The filter of this invention disconnects the original parallel open-circuit stubs and connects them with PIN diodes. The length of the open-circuit stubs connected in parallel to the HMCSIW is controlled by turning the PIN diodes on and off, thereby controlling the resonant frequency of the open circuit. This changes the low-frequency zero point of the filter, and consequently, the bandwidth and center frequency of the entire filter. This filter achieves two different low-frequency zero points through external voltage control without changing the filter's structural dimensions. It is reconfigurable, can be combined with differential transmission lines, has common-mode rejection characteristics, and possesses multiple functions. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the structure of the first metal layer of the present invention.

[0027] Figure 2 This is a structural diagram of the PIN diode on the first metal layer of this invention.

[0028] Figure 3 This is a schematic diagram of the structure of the second metal layer of the present invention.

[0029] Figure 4 This is a graph showing the relationship between S-parameters and frequency during differential simulation of the present invention.

[0030] Figure 5 This is a graph showing the relationship between S-parameters and frequency during the simulation of this invention.

[0031] Figure 6 This is a schematic diagram of the structure of the present invention. Detailed Implementation

[0032] 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 invention. That is, in some embodiments of the invention, these practical details are not essential.

[0033] like Figure 1-3As shown, this invention is a reconfigurable differential filter based on HMCSIW. The reconfigurable differential filter comprises, from top to bottom, a first metal layer, a first dielectric substrate, a second metal layer, another second dielectric substrate, and a third metal layer. The lower surface of the first dielectric substrate and the upper surface of the second dielectric substrate form the second metal layer, and the lower surface of the second dielectric layer forms the third metal layer. The structure of the third metal layer is the same as that of the first metal layer. The first metal layer is disposed on the upper surface of the first dielectric substrate and includes an HMCSIW rectangular patch 1, a pair of trapezoidal microstrip lines 2, a pair of L-shaped quarter-wavelength open-circuit stubs 3, and a DBCSRR structure. 4. Several comb-like open-circuit stubs 8 and L-shaped quarter-wavelength open-circuit stubs 3 are provided on the HMCSIW rectangular patch 1. The L-shaped quarter-wavelength open-circuit stubs 3 are connected in parallel with the HMCSIW rectangular patch 1 and placed near the two side edges of the HMCSIW rectangular patch 1. This is because the position of the open-circuit stub is related to the number and position of poles in the passband. When the position of the open-circuit stub is closer to the central axis, its resonant point and the resonant point of DBCSRR will affect each other, causing the poles of the two to approach each other. When they reach a certain position, the poles of the two will coincide. In order to make the passband have two poles, the passband is wider, and the rectangularity factor is better, the open-circuit stubs are placed near the two side edges of the rectangular patch.

[0034] Each of the L-shaped quarter-wavelength open-circuit stubs 3 is disconnected and connected with a PIN diode 5. The length of the L-shaped quarter-wavelength open-circuit stub 3 is controlled by turning the PIN diode 5 on and off, thereby controlling the resonant frequency of the open-circuit stub. The low-frequency zero point of the filter will change, and the bandwidth and center frequency of the entire filter will change accordingly. There are ports and microstrip lines on both sides of the trapezoidal microstrip line 2, and the impedance of each is 50Ω.

[0035] A rectangular slot 6 is etched on the second metal layer. A folded SSPPs structure 7 is disposed on one side of the rectangular slot 6 near the open edge. The width of the rectangular slot 6 is related to the strength of common-mode suppression; the wider the rectangular slot 6, the stronger the common-mode suppression. At its strongest, its width is the same as the width of the rectangular patch. The total length of the folded SSPPs structure 7 is determined according to the frequency range of common-mode suppression. The longer the folded SSPPs structure 7, the lower the frequency range of common-mode suppression. Its total length is adjusted between 5.5-6 mm. The width of the rectangular slot 6 is 13.5 mm, the length of the rectangular slot 6 is 20 mm, and the total length of the folded SSPPs structure 7 is 5.6 mm. The spacing between two adjacent branches in the folded SSPPs structure 7 is adjusted between 1.4-1.6 mm, preferably 1.5 mm.

[0036] The length of the L-shaped quarter-wavelength open-circuit stub 3 on the first and third metal layers is determined according to the frequency of the low-frequency zero and is adjusted between 5.3-5.7 mm. The preferred length of the L-shaped quarter-wavelength open-circuit stub 3 is 5.7 mm. The longer the L-shaped quarter-wavelength open-circuit stub 3, the lower the frequency of the low-frequency zero. The position of the L-shaped quarter-wavelength open-circuit stub 3 is related to the number and position of the poles in the passband. The distance from the center is determined according to the position of the poles in the passband and is adjusted between 8.1-9.7 mm, preferably 8.1 mm. When the position of the L-shaped quarter-wavelength open-circuit stub 3 moves closer to the central axis, its resonant point and the resonant point of the DBCSRR will affect each other, causing their poles to approach each other. When they reach a certain position, their poles will coincide. In order to have two poles in the passband, a wider passband, and a better rectangularity factor, the open-circuit stub is placed close to the two edges of the rectangular patch.

[0037] The position of PIN diode 5 is determined based on the frequency difference of the low-frequency zero point when the PIN diode is turned on and off, and the magnitude of the return loss in the passband. In order to make the return loss in the passband lower than -15dB, the length of the disconnected microstrip that is not connected to the open edge of HMCSIW is adjusted between 0.7-1.1mm. The PIN diode 5 is all of the MADP-000907-14020 type. When turned on, the PIN diode 5 is equivalent to a 5.2Ω resistor, and when turned off, the PIN diode 5 is equivalent to a 0.025pF capacitor.

[0038] The DBCSRR structure 4 on the first and third metal layers is placed in the center, making the entire filter structure symmetrical. The size of the DBCSRR structure 4 is determined by the frequency of the high-frequency zero. The larger the size of the DBCSRR structure 4, the lower the frequency of the high-frequency zero. To obtain a large bandwidth, it is often desirable to have a high frequency of the high-frequency zero and a low frequency of the low-frequency zero. However, if the size of the DBCSRR is too small, it will be difficult to manufacture. The DBCSRR structure 4 includes an inner ring and an outer ring. Both the inner and outer rings have openings, but the openings of the inner ring and the outer ring do not correspond. The diameter of the outer ring of the DBCSRR structure 4 is adjusted between 3.1-3.5 mm, preferably 3.2 mm. The width of both the inner and outer rings is 0.2 mm, the distance between the inner and outer rings is 0.2 mm, and the distance between the openings is 0.2 mm.

[0039] The length of the HMCSIW rectangular patch 1 is 20mm, and the width of the HMCSIW rectangular patch 1 is determined according to the operating frequency range of the filter, and is adjusted between 13-14mm, preferably 13.5mm. The length of the comb-like open stub 8 is 5.5mm, the width of the comb-like open stub 8 is 0.5mm, the distance between two adjacent comb-like open stubs 8 is 1mm, and the lower base of the trapezoidal microstrip line 2 is 4.5mm, the upper base is 1.5mm, and the height is 15mm.

[0040] Both the first and second dielectric substrates are made of Rogers 5880 material, and both have a thickness of 0.508 mm.

[0041] The simulation results of this invention are as follows: Figures 4-5 As shown, Figure 4 For differential simulation, a comparison diagram of the S-parameters of the PIN diode 5 when it is on and off is provided. When all four PIN diodes are on, the filter has a low-frequency zero of 10.05 GHz, a relative bandwidth of 20.7%, and a center frequency of 12.1 GHz. When all four PIN diodes are off, the low-frequency zero is 11.15 GHz, the relative bandwidth is 13.8%, and the center frequency is 12.5 GHz. The return loss is less than -15 dB in the passband frequency range under both states.

[0042] Figure 5 The S-parameter comparison diagrams for the PIN diode during common-mode simulation show that the common-mode rejection is below -40dB across the frequency range in both states, demonstrating excellent common-mode rejection characteristics. The filter exhibits good filtering performance in all states, indicating that the structure of this invention not only achieves adjustable low-frequency zero-point but also possesses high common-mode rejection and performs well across all states.

[0043] The filter of this invention disconnects the original parallel open-circuit stub and connects it with a PIN diode. The length of the open-circuit stub connected in parallel to the HMCSIW is controlled by turning the PIN diode on and off, thereby controlling the resonant frequency of the open-circuit stub. This changes the low-frequency zero point of the filter, and consequently, the bandwidth and center frequency of the entire filter. This filter can achieve two different low-frequency zero points through external voltage control without changing the filter's structural dimensions. It is reconfigurable, can be combined with differential transmission lines, has common-mode rejection characteristics, and possesses multiple functions.

[0044] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A reconfigurable differential filter based on HMCSIW, wherein the reconfigurable differential filter is provided with a first metal layer, a first dielectric substrate, a second metal layer, a second dielectric substrate, and a third metal layer sequentially from top to bottom, wherein the lower surface of the first dielectric substrate and the upper surface of the second dielectric substrate constitute the second metal layer, and the lower surface of the second dielectric substrate constitutes the third metal layer, wherein the structure of the third metal layer is the same as the structure of the first metal layer, characterized in that: The first metal layer is disposed on the upper surface of the first dielectric substrate. The first metal layer includes an HMCSIW rectangular patch (1), a trapezoidal microstrip line (2), a pair of L-shaped quarter-wavelength open-circuit stubs (3), and a DBCSRR structure (4). Several comb-like open-circuit stubs (8) and L-shaped quarter-wavelength open-circuit stubs (3) are disposed on the HMCSIW rectangular patch (1). The L-shaped quarter-wavelength open-circuit stubs (3) are connected in parallel with the HMCSIW rectangular patch (1) and are disposed near the two side edges of the HMCSIW rectangular patch (1). Each L-shaped quarter-wavelength open-circuit stub (3) is arranged in parallel with the HMCSIW rectangular patch (1). The wavelength open-circuit stub (3) is disconnected and connected with a PIN diode (5). The length of the L-type quarter-wavelength open-circuit stub (3) is controlled by the conduction and turn-off of the PIN diode (5), thereby controlling its resonant frequency. The low-frequency zero point of the filter will change, and the bandwidth and center frequency of the entire filter will change accordingly. The DBCSRR structure (4) on the first and third metal layers is placed in the center position, making the entire filter structure symmetrical from left to right. The size of the DBCSRR structure (4) is determined according to the frequency of the high-frequency zero point. The larger the size of the DBCSRR structure (4), the lower the frequency of the high-frequency zero point.

2. The reconfigurable differential filter based on HMCSIW according to claim 1, characterized in that: The width of the HMCSIW rectangular patch (1) is determined according to the operating frequency of the filter, specifically: in: The equivalent width of the rectangular patch. d is the actual width of the rectangular patch, s is the width of the comb-like microstrip stub, h is the spacing between two adjacent microstrip stubs, and the operating frequency band is TE. 10 Cutoff frequency to TE in mode 20 Cutoff frequency in the mode.

3. A reconfigurable differential filter based on HMCSIW according to claim 1, characterized in that: A rectangular slit (6) is etched on the second metal layer. Folded SSPPs structures (7) are equidistantly arranged at one end of the rectangular slit (6). The width of the rectangular slit (6) is related to the strength of common mode suppression. The wider the rectangular slit (6), the stronger the common mode suppression. The length of the folded SSPPs structure (7) is determined according to the frequency range of common mode suppression. The longer the length of the folded SSPPs structure (7), the lower the frequency range of common mode suppression.

4. A reconfigurable differential filter based on HMCSIW according to claim 1, characterized in that: The length of the L-shaped quarter-wavelength open stub (3) on the first and third metal layers is determined according to the frequency of the low-frequency zero. The longer the L-shaped quarter-wavelength open stub (3), the lower the frequency of the low-frequency zero.

5. A reconfigurable differential filter based on HMCSIW according to claim 1 or 4, characterized in that: The closer the disconnection position of the L-type quarter-wavelength open-circuit stub (3) is to the central axis, the smaller the change in the low-frequency zero point when the PIN diode (5) is turned on and off.

6. A reconfigurable differential filter based on HMCSIW according to claim 1, characterized in that: The DBCSRR structure (4) includes an inner ring and an outer ring, both of which have openings, and the openings of the inner ring and the outer ring do not correspond to each other.

7. A reconfigurable differential filter based on HMCSIW according to claim 1, characterized in that: There are ports and microstrip lines on both sides of the trapezoidal microstrip line (2), and both have an impedance of 50Ω.

Images