An actively adjustable low-pass and band-pass switchable artificial surface plasmon filter

Abstract

The present invention discloses an active, adjustable low-pass and bandpass switchable artificial surface plasmon filter, comprising a first dielectric plate, a second dielectric plate, and a metal ground between the two. A first metal layer is provided on the front surface of the first dielectric plate, on which a tunable artificial surface plasmon unit is etched. A transition unit and a feeding structure are symmetrically connected at both ends of the tunable artificial surface plasmon unit. The feeding structure is used to connect the signal to be filtered and is connected to the tunable artificial surface plasmon unit through the transition unit. The present invention can switch the artificial surface plasmon filter between low-pass and bandpass effects, adjusting the upper cutoff frequency of the low-pass artificial surface plasmon filter and separately adjusting the upper and lower cutoff frequencies of the bandpass artificial surface plasmon filter.

Description

Technical Field

[0001] The present invention relates to an artificial surface plasmon filter, in particular to an artificial surface plasmon filter with active adjustable low-pass and switchable band-pass. Background Art

[0002] Surface plasmon polaritons (SPPs), originally proposed in the field of optics, are surface electromagnetic waves formed by the interaction between surface charges and the electromagnetic field of light. Surface plasmons generally propagate along the surfaces of two materials with opposite dielectric constants, offering unique advantages such as strong field confinement. Etching arrays of holes on a metal surface can achieve an equivalent negative dielectric constant at low frequencies and produce a dispersion phenomenon similar to that of surface plasmons, resulting in artificial surface plasmons (SSPPs).

[0003] In modern communication systems, microwave filters are widely used to suppress spurious signals, filter out noise, and improve signal quality and transmission efficiency. To meet the requirements of modern intelligent communication systems for receiving and processing signals of varying frequencies, the need for reconfigurable filters is urgent. Numerous tunable filters based on traditional microstrip coupling structures have been proposed, but these typically exhibit narrow bandwidths and complex structures. Filters based on artificial surface plasmons (SPPs) exhibit broadband characteristics, and their dispersion characteristics can be arbitrarily controlled by the geometric features of the unit cell, greatly simplifying the design process. Therefore, reconfigurable communication systems based on SPPs hold broad application prospects.

[0004] The most commonly used filters in communication systems are low-pass and band-pass filters. However, existing filters based on artificial surface plasmons are mostly low-pass filters that cannot be switched to band-pass filters, and the upper cutoff frequency of the low-pass filters cannot be adjusted. Summary of the Invention

[0005] The object of the present invention is to provide an actively adjustable low-pass and band-pass switchable artificial surface plasmon filter, which can switch between low-pass and band-pass, and can adjust the upper cutoff frequency of the low-pass filter and the upper and lower cutoff frequencies of the band-pass filter.

[0006] To achieve the above objectives, the present invention provides an active, adjustable low-pass, band-pass switchable artificial surface plasmon filter, comprising a first dielectric plate, a second dielectric plate, and a metal ground between the first and second dielectric plates. A first layer of metal is provided on the front surface of the first dielectric plate, and a tunable artificial surface plasmon unit is etched on the first layer of metal. A transition unit and a feeding structure are symmetrically connected at both ends of the tunable artificial surface plasmon unit. The feeding structure is used to connect a signal to be filtered and is connected to the tunable artificial surface plasmon unit through the transition unit. DC bias circuit three is respectively provided on the upper and lower sides of the first layer of metal. A third layer of metal is provided on the reverse side of the second dielectric plate, and DC bias circuit one, DC bias circuit two, and DC bias circuit four are provided on the third layer of metal.

[0007] The tunable artificial surface plasmon unit includes a traditional artificial surface plasmon unit, a metal branch, and a first group of varactor diodes. The traditional artificial surface plasmon unit is a square hole etched in a microstrip line, and its two sides are respectively connected to one end of the first group of varactor diodes. The other end of the first group of varactor diodes is connected to one end of the metal branch. The metal branch is a U-shaped structure bent inward. A tunable artificial surface plasmon unit includes four metal branches, which are symmetrically arranged in top, bottom, left and right.

[0008] The first group of varactor diodes is used to adjust the upper cutoff frequency of the band-pass and low-pass filters.

[0009] From left to right, the metal branches of the odd-numbered tunable artificial surface plasmon units are connected to the DC bias circuit three through the DC blocking inductor one; the metal branches of the even-numbered tunable artificial surface plasmon units are connected to the DC bias circuit four through the DC blocking inductor two and the metal through-hole two.

[0010] From left to right, the left center position of the odd-numbered tunable artificial surface plasmon unit is connected to DC bias circuit one through DC blocking inductor three and metal through-hole one; the left center position of the even-numbered tunable artificial surface plasmon unit is connected to DC bias circuit two through DC blocking inductor three and metal through-hole one.

[0011] The tunable artificial surface plasmon units are connected via a second set of varactor diodes, two of which are arranged in parallel. By controlling the on and off of the second set of varactor diodes and different reverse bias voltages, the switching between the low-pass and band-pass filters and the adjustment of the cutoff frequency of the band-pass filter are achieved.

[0012] As a further solution of the present invention: the number of the tunable artificial surface plasmon units is N, the N tunable artificial surface plasmon units are connected in series, the starting end and the tail end of the tunable artificial surface plasmon unit are respectively connected in series with M transition units, the length of the wide side connecting the transition unit and the feeding structure is less than the length of the wide side connecting the transition unit and the tunable artificial surface plasmon unit, the number of the transition units is 2M, and the width of the transition unit gradually increases from the feeding structure to the tunable artificial surface plasmon unit; wherein M and N are both integers greater than or equal to 1, and M <N。

[0013] The tunable artificial surface plasmon unit is used to convert the fed quasi-TEM wave into a TM wave, and to perform dispersion control through a DC bias voltage, thereby changing the upper cutoff frequency.

[0014] As a further solution of the present invention, the potential difference between DC bias circuit one and DC bias circuit two is used to drive a second group of varactor diodes; the potential difference between DC bias circuit one and DC bias circuit three is equal to the potential difference between DC bias circuit two and DC bias circuit four, and are used to drive the first group of varactor diodes of odd-numbered tunable artificial surface plasmon units and the first group of varactor diodes of even-numbered tunable artificial surface plasmon units, respectively.

[0015] As a further solution of the present invention: the first dielectric plate and the second dielectric plate are both made of Rogers RT5880 material, with a relative dielectric constant of 2.2 and a loss tangent of 0.0009. The thickness of the first dielectric plate is 0.787 mm, and the thickness of the second dielectric plate is 0.508 mm.

[0016] As a further solution of the present invention: the distance between the two second groups of variable capacitance diodes (72) connected in parallel is 4 mm.

[0017] Compared with the prior art, the present invention provides an actively adjustable low-pass and bandpass switchable artificial surface plasmon filter. The dispersion characteristics of the artificial surface plasmon waveguide are controlled by a first group of varactor diodes and metal branches, thereby adjusting the upper cutoff frequency of the low-pass and bandpass artificial surface plasmon filters. At the same time, the metal branches are bent inward, which can greatly reduce the overall size and ensure the compactness of the structure. By controlling the on and off of the second group of varactor diodes, the artificial surface plasmon filter can be switched between low-pass and bandpass effects. By controlling the reverse bias voltage of the second group of varactor diodes, the capacitance value of the second group of varactor diodes is changed, thereby adjusting the lower cutoff frequency of the bandpass artificial surface plasmon filter. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of the present invention.

[0019] Figure 2 This is a rear view of the second dielectric plate in the present invention.

[0020] Figure 3 yes Figure 1 Top view of .

[0021] Figure 4 This is a dispersion curve diagram of the tunable artificial surface plasmon unit in the present invention.

[0022] Figure 5 It is a transmission coefficient diagram of the present invention in the low-pass state.

[0023] Figure 6 It is a transmission coefficient diagram of the present invention in the bandpass state.

[0024] In the figure: 1. first dielectric plate, 2. second dielectric plate, 3. feeding structure, 4. transition unit, 5. tunable artificial surface plasmon unit, 11. first metal layer, 21. metal ground, 31. third metal layer, 51. metal branch, 61. metal through hole 1, 62. metal through hole 2, 71. first group of varactor diodes, 72. second group of varactor diodes, 81. DC blocking inductor 1, 82. DC blocking inductor 2, 83. DC blocking inductor 3, 91. DC bias circuit 1, 92. DC bias circuit 2, 93. DC bias circuit 3, 94. DC bias circuit 4. DETAILED DESCRIPTION

[0025] The present invention will be further described below with reference to the accompanying drawings.

[0026] like Figures 1 to 3 As shown, an active, tunable low-pass, bandpass, switchable artificial surface plasmon filter comprises a first dielectric plate 1, a second dielectric plate 2, and a metal ground 21 between the first and second dielectric plates 1 and 2. A first metal layer 11 is provided on the front surface of the first dielectric plate 1, on which a tunable artificial surface plasmon unit 5 is etched. A transition unit 4 and a feed structure 3 are symmetrically connected at both ends of the tunable artificial surface plasmon unit 5. The feed structure 3 is used to receive the signal to be filtered and is connected to the tunable artificial surface plasmon unit 5 through the transition unit 4. A third DC bias circuit 93 is provided on the upper and lower sides of the first metal layer 11, respectively. A third metal layer 31 is provided on the reverse side of the second dielectric plate 2, on which a first DC bias circuit 91, a second DC bias circuit 92, and a fourth DC bias circuit 94 are provided. DC bias circuit three 93 and the tunable artificial surface plasmon unit 5 are located on the same first metal layer 11, and DC bias circuit one 91, DC bias circuit two 92, and DC bias circuit four 94 are located on the third metal layer 31, effectively avoiding the possibility of cross connection between different bias circuits.

[0027] The tunable artificial surface plasmon unit 5 includes a traditional artificial surface plasmon unit, a metal branch 51, and a first group of varactor diodes 71. The traditional artificial surface plasmon unit is a square hole etched in the microstrip line, and its two sides are respectively connected to one end of the first group of varactor diodes 71, and the other end of the first group of varactor diodes 71 is connected to one end of the metal branch 51. The metal branch 51 is a U-shaped structure bent inward, which can reduce the overall size; a tunable artificial surface plasmon unit 5 includes four metal branches 51, which are symmetrically arranged in the upper and lower left and right directions; from left to right, the metal branches 51 of the odd-numbered tunable artificial surface plasmon units 5 are connected to the DC bias circuit three 93 through the DC blocking inductor 1 81; the metal branches 51 of the even-numbered tunable artificial surface plasmon units 5 are connected to the DC bias circuit four 94 through the DC blocking inductor 2 82 and the metal through-hole 2 62.

[0028] The first group of varactor diodes 71 is used to adjust the upper cutoff frequency of the band-pass and low-pass filters.

[0029] From left to right, the left center position of the odd-numbered tunable artificial surface plasmon unit 5 is connected to the DC bias circuit 1 91 through the DC blocking inductor 3 83 and the metal through-hole 1 61; the left center position of the even-numbered tunable artificial surface plasmon unit 5 is connected to the DC bias circuit 2 92 through the DC blocking inductor 3 83 and the metal through-hole 1 61.

[0030] The tunable artificial surface plasmon units 5 are connected through a second group of varactor diodes 72. Two second groups of varactor diodes 72 are arranged in parallel. By controlling the on and off of the second group of varactor diodes 72 and different reverse bias voltages, the switching of the low-pass and band-pass filters and the adjustment of the lower cutoff frequency of the band-pass filter are achieved.

[0031] The potential difference between the DC bias circuit 1 91 and the DC bias circuit 2 92 is used to drive the second set of varactor diodes 72 .

[0032] The potential difference between DC bias circuit 1 91 and DC bias circuit 3 93 is equal to the potential difference between DC bias circuit 2 92 and DC bias circuit 4 94 , and they are used to drive the first group of varactor diodes 71 of the odd-numbered tunable artificial surface plasmon units 5 and the first group of varactor diodes 71 of the even-numbered tunable artificial surface plasmon units 5 , respectively.

[0033] The number of tunable artificial surface plasmon units 5 is N, and the N tunable artificial surface plasmon units 5 are connected in series. The starting end and the tail end of the tunable artificial surface plasmon unit 5 are respectively connected in series with M transition units 4, the width length of the transition unit 4 connected to the feeding structure 3 is less than the width length of the transition unit 4 connected to the tunable artificial surface plasmon unit 5, the total number of transition units 4 is 2M, and the width of the transition unit 4 gradually increases from the feeding structure 3 to the tunable artificial surface plasmon unit 5; the starting end and the tail end of the N tunable artificial surface plasmon units 5 are each connected in series with M transition units; wherein M and N are integers greater than or equal to 1, and M <N。

[0034] The tunable artificial surface plasmon unit 5 is used to convert the fed quasi-TEM wave into a TM wave, and to perform dispersion control through a DC bias voltage, thereby changing the upper cutoff frequency of the low-pass and band-pass artificial surface plasmon filters.

[0035] The distance between the two second groups of varactors 72 connected in parallel is 4 mm.

[0036] The first dielectric plate 1 and the second dielectric plate 2 are both made of Rogers RT5880 material, with a relative dielectric constant of 2.2 and a loss tangent of 0.0009. The thickness of the first dielectric plate 1 is 0.787 mm, and the thickness of the second dielectric plate 2 is 0.508 mm.

[0037] Example:

[0038] Set M=2, N=7, such as Figures 1 to 3 As shown, an active adjustable low-pass, band-pass switchable artificial surface plasmon filter includes a first dielectric plate 1, a second dielectric plate 2, and a metal ground 21 between the first dielectric plate 1 and the second dielectric plate 2. A first layer of metal 11 is provided on the front of the first dielectric plate 1, and seven tunable artificial surface plasmon units 5 are etched on the first layer of metal 11. The two ends of the tunable artificial surface plasmon unit 5 are symmetrically connected to a transition unit 4 and a feeding structure 3, wherein there are four transition units 4 in total. 5 is respectively connected in series with two transition units 4 at the starting end and the tail end; the width length of the transition unit 4 connected to the feeding structure 3 is less than the width length of the transition unit 4 connected to the tunable artificial surface plasmon unit 5, and DC bias circuit three 93 are respectively provided on the upper and lower sides of the first layer of metal 11; a third layer of metal 31 is provided on the reverse side of the second dielectric plate 2, and a DC bias circuit one 91, a DC bias circuit two 92, and a DC bias circuit four 94 are provided on the third layer of metal 31, which can provide bias voltages V1, V2, and V4, respectively.

[0039] The feed structure 3 is a microstrip line with a characteristic impedance of 50 ohms. The left and right feed structures 3 are both welded with SMA connectors for connecting to other microwave devices. The first dielectric plate 1 and the second dielectric plate 2 are both made of Rogers RT5880 material with a relative dielectric constant of 2.2 and a loss tangent of 0.0009. The size of the first dielectric plate 1 is 125.3*20*0.787mm. 3 The size of the second dielectric plate 2 is 80*20*0.508mm 3 .

[0040] The tunable artificial surface plasmon unit 5 includes a traditional artificial surface plasmon unit, a metal branch 51, and a first group of varactor diodes 71, wherein the traditional artificial surface plasmon unit is a square hole etched in the microstrip line with a width of 5.62mm, and its two sides are respectively connected to one end of the first group of varactor diodes 71, and the other end of the first group of varactor diodes 71 is connected to one end of the metal branch 51. The metal branch 51 is a U-shaped structure bent inward, with a total length of 9mm and a width of 0.7mm. A tunable artificial surface plasmon unit 5 includes four metal branches 51, which are symmetrically arranged in the upper and lower left and right directions. The dispersion characteristics of the artificial surface plasmon waveguide can be regulated by the first group of varactor diodes 71 and the metal branches 51. Figure 4 As shown, when the capacitance values ​​of the first group of varactor diodes 71 are set to 0.025 pF, 0.1 pF and 0.19 pF respectively, the dispersion curve of the tunable artificial surface plasmon unit gradually deviates from the dispersion curve of the microstrip line and presents different upper cutoff frequencies.

[0041] The transition units 4 are symmetrically distributed at both ends of the tunable artificial surface plasmon unit 5 and connected to the feeding structure 3. The width thereof gradually increases from the feeding structure 3 to the tunable artificial surface plasmon unit 5, which are 3.34 mm and 4.48 mm respectively.

[0042] like Figure 1 As shown, from left to right, the metal branches 51 in the 1st, 3rd, 5th and 7th tunable artificial surface plasmon units 5 are connected to the DC bias circuit 3 93 of the same layer through the DC blocking inductor 1 81, and the bias voltage provided is V3; the metal branches 51 in the 2nd, 4th and 6th tunable artificial surface plasmon units 5 are connected to the DC bias circuit 4 94 through the DC blocking inductor 2 82 and the metal through-hole 2 62, and the bias voltage provided is V4.

[0043] From left to right, the left center positions of the 1st, 3rd, 5th, and 7th tunable artificial surface plasmon units 5 are connected to the DC bias circuit 1 91 through the DC blocking inductor 3 83 and the metal through-hole 1 61, and the bias voltage provided is V1; the left center positions of the 2nd, 4th, and 6th tunable artificial surface plasmon units 5 are connected to the DC bias circuit 2 92 through the DC blocking inductor 3 83 and the metal through-hole 1 61, and the bias voltage provided is V2.

[0044] Each tunable artificial surface plasmon unit 5 is connected via two parallel second sets of varactor diodes 72. The direction of the second set of varactor diodes 72 is positive on the left and negative on the right, and the parallel spacing is 4mm. When the bias voltage V1-V2 is greater than 0, the second set of varactor diodes 72 is turned on. At this time, the filter provided by this embodiment is in a low-pass state. At the same time, the capacitance value of the first set of varactor diodes 71 can be controlled by the bias voltages V1-V3 and V2-V4 to adjust the upper cutoff frequency of the low-pass filter. Figure 5 As shown in FIG. 1 , when the capacitance value of the first group of varactor diodes 71 increases from 0.025 pF to 0.19 pF, the upper cut-off frequency gradually decreases.

[0045] When the bias voltage V1-V2 is less than 0, the second set of varactor diodes 72 is cut off. At this time, the filter provided by this embodiment is in a bandpass state. Different bias voltages V1-V2 make the second set of diodes 72 show different capacitance values, thereby making the bandpass filter show different lower cutoff frequencies. Figure 6 As shown in FIG. 1 , when the capacitance of the second set of varactor diodes 72 increases from 0.4 pF to 1 pF, the lower cutoff frequency gradually decreases. At this time, the upper cutoff frequency of the bandpass filter can still be adjusted by the first set of varactor diodes 71 .

Claims

1. An active adjustable low-pass and band-pass switchable artificial surface plasmon filter, comprising a first dielectric plate (1), a second dielectric plate (2), and a metal ground (21) between the first dielectric plate (1) and the second dielectric plate (2), characterized in that: The front surface of the first dielectric plate (1) is provided with a first layer of metal (11), a tunable artificial surface plasmon unit (5) is etched on the first layer of metal (11), and the two ends of the tunable artificial surface plasmon unit (5) are symmetrically connected to a transition unit (4) and a feeding structure (3), the feeding structure (3) is used to connect the signal to be filtered and is connected to the tunable artificial surface plasmon unit (5) through the transition unit (4); a DC bias circuit three (93) is provided on the upper and lower sides of the first layer of metal (11), respectively; a third layer of metal (31) is provided on the reverse side of the second dielectric plate (2), and a DC bias circuit one (91), a DC bias circuit two (92), and a DC bias circuit four (94) are provided on the third layer of metal (31); The tunable artificial surface plasmon unit (5) includes a conventional artificial surface plasmon unit, a metal branch (51), and a first group of variable capacitance diodes (71). The conventional artificial surface plasmon unit is a square hole etched in a microstrip line, and its two sides are respectively connected to one end of the first group of variable capacitance diodes (71). The other end of the first group of variable capacitance diodes (71) is connected to one end of the metal branch (51). The metal branch (51) is a U-shaped structure bent inward. A tunable artificial surface plasmon unit (5) includes four metal branches (51) that are symmetrically arranged in the upper and lower directions. The first group of varactor diodes (71) is used to adjust the upper cutoff frequency of the bandpass and lowpass filters; From left to right, the metal branches (51) of the odd-numbered tunable artificial surface plasmon units (5) are connected to the DC bias circuit three (93) through the DC blocking inductor one (81); the metal branches (51) of the even-numbered tunable artificial surface plasmon units (5) are connected to the DC bias circuit four (94) through the DC blocking inductor two (82) and the metal through hole two (62); From left to right, the left center position of the odd-numbered tunable artificial surface plasmon unit (5) is connected to the DC bias circuit one (91) through the DC blocking inductor three (83) and the metal through hole one (61); the left center position of the even-numbered tunable artificial surface plasmon unit (5) is connected to the DC bias circuit two (92) through the DC blocking inductor three (83) and the metal through hole one (61); The tunable artificial surface plasmon units (5) are connected via a second group of variable capacitance diodes (72), two of which are arranged in parallel; by controlling the on / off state of the second group of variable capacitance diodes (72) and different reverse bias voltages, the switching between the low-pass and band-pass filters and the adjustment of the cut-off frequency of the band-pass filter are achieved.

2. The active tunable low-pass and band-pass switchable artificial surface plasmon filter according to claim 1, characterized in that: The number of the tunable artificial surface plasmon units (5) is N, and the N tunable artificial surface plasmon units (5) are connected in series; the starting end and the tail end of the tunable artificial surface plasmon unit (5) are respectively connected in series with M transition units (4), the width length of the transition unit (4) connected to the feeding structure (3) is less than the width length of the transition unit (4) connected to the tunable artificial surface plasmon unit (5), the total number of the transition units (4) is 2M, and the width of the transition unit (4) gradually increases from the feeding structure (3) to the tunable artificial surface plasmon unit (5); wherein M and N are both integers greater than or equal to 1, and M <N; The tunable artificial surface plasmon unit (5) is used to convert the fed quasi-TEM wave into a TM wave, and to perform dispersion control through a DC bias voltage, thereby changing the upper cutoff frequency.

3. The active adjustable low-pass and band-pass switchable artificial surface plasmon filter according to claim 1, characterized in that: The potential difference between the DC bias circuit 1 (91) and the DC bias circuit 2 (92) is used to drive the second group of variable capacitance diodes (72); the potential difference between the DC bias circuit 1 (91) and the DC bias circuit 3 (93) is equal to the potential difference between the DC bias circuit 2 (92) and the DC bias circuit 4 (94), and is used to drive the first group of variable capacitance diodes (71) of the odd-numbered tunable artificial surface plasmon units (5) and the first group of variable capacitance diodes (71) of the even-numbered tunable artificial surface plasmon units (5), respectively.

4. The active tunable low-pass and band-pass switchable artificial surface plasmon filter according to claim 1, characterized in that: The first dielectric plate (1) and the second dielectric plate (2) are both made of Rogers RT5880 material, with a relative dielectric constant of 2.2 and a loss tangent of 0.0009. The thickness of the first dielectric plate (1) is 0.787 mm, and the thickness of the second dielectric plate (2) is 0.508 mm.

5. The active adjustable low-pass and band-pass switchable artificial surface plasmon filter according to claim 1, characterized in that: The distance between the two second groups of varactor diodes (72) connected in parallel is 4 mm.

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