Active adjustable low-pass and band-pass switchable artificial surface plasmon filter

Abstract

The invention discloses an active adjustable low-pass and band-pass switchable artificial surface plasmon filter which comprises a first dielectric plate, a second dielectric plate and a metal ground between the first dielectric plate and the second dielectric plate, a first layer of metal is arranged on the front face of the first dielectric plate, a tunable artificial surface plasmon unit is etched on the first layer of metal, and a second layer of metal is etched on the second layer of metal. Two ends of the tunable artificial surface plasmon unit are symmetrically connected with a transition unit and a feed structure, and the feed structure is used for connecting a signal to be filtered and is connected with the tunable artificial surface plasmon unit through the transition unit. Switching of the artificial surface plasmon filter between the low-pass effect and the band-pass effect can be achieved, the upper cut-off frequency of the low-pass artificial surface plasmon filter can be adjusted, and the upper cut-off frequency and the lower cut-off frequency of the band-pass artificial surface plasmon filter can also be adjusted respectively.

Description

Technical Field

[0001] The 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] As a surface electromagnetic wave, surface plasmons (SPPs) were originally proposed in the field of optics. They are composed of 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. They have unique advantages, such as strong field confinement. Etching an array of holes on the surface of a metal can achieve an equivalent negative dielectric constant at low frequencies and produce a dispersion phenomenon similar to surface plasmons, which is called artificial surface plasmons (Spoof Surface Plasmon Polaritons, SSPPs).

[0003] In modern communication systems, microwave filters are widely used to suppress stray signals, filter out noise, and improve signal quality and transmission efficiency. In order to meet the requirements of modern intelligent communication systems for receiving and processing signals of different frequencies, the demand for reconfigurable filters is urgent. At present, many tunable filters based on traditional microstrip coupling structures have been proposed, which usually have narrow bandwidths and complex structures. Filters based on artificial surface plasmons have broadband characteristics, and their dispersion characteristics can be arbitrarily controlled by the geometric characteristics of the unit, which greatly simplifies the design difficulty. Therefore, reconfigurable communication systems based on artificial surface plasmons have broad application prospects.

[0004] The most commonly used filters in communication systems are low-pass and band-pass filters, but the 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 active 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-mentioned purpose, 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 dielectric plate and the second dielectric plate, wherein a first layer of metal is provided on the front side of the first dielectric plate, a tunable artificial surface plasmon unit is etched on the first layer of metal, and transition units and feeding structures 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; a DC bias circuit three is provided on the upper and lower sides of the first layer of metal, respectively, a third layer of metal is provided on the reverse side of the second dielectric plate, and a DC bias circuit one, a DC bias circuit two, and a 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 variable capacitance 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 variable capacitance diodes, and the other end of the first group of variable capacitance 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 the upper and lower left and right directions.

[0008] The first group of varactor diodes is used to adjust the upper cutoff frequency of the bandpass and lowpass 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] 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 with the feeding structure is less than the length of the wide side connecting the transition unit with 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;

[0012] 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.

[0013] As a further solution of the present invention: the tunable artificial surface plasmon units are connected by a second group of varactor diodes, and two of the second group of varactor diodes are arranged in parallel; by controlling the on and off of the second group of varactor diodes and different reverse bias voltages, the switching of low-pass and band-pass filters and the adjustment of the cutoff frequency of the band-pass filter are achieved.

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

[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, a loss tangent of 0.0009, a thickness of the first dielectric plate of 0.787 mm, and a thickness of the second dielectric plate of 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 active adjustable low-pass and band-pass switchable artificial surface plasmon filter of the present invention regulates the dispersion characteristics of the artificial surface plasmon waveguide through a first group of varactor diodes and metal branches, thereby adjusting the upper cutoff frequency of the low-pass and band-pass 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-off of the second group of varactor diodes, the switching of the artificial surface plasmon filter between the low-pass and band-pass effects is achieved; 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 achieving the adjustment of the lower cutoff frequency of the band-pass artificial surface plasmon filter. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0021] Figure 4 It 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 layer of metal, 21. metal ground, 31. third layer of metal, 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 in conjunction with the accompanying drawings.

[0026] like Figures 1 to 3 As shown, an active adjustable low-pass, band-pass switchable artificial surface plasmon filter comprises 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 a tunable artificial surface plasmon unit 5 is etched on the first layer of metal 11. Transition units 4 and feeding structures 3 are symmetrically connected at both ends of the tunable artificial surface plasmon unit 5. 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. DC bias circuit three 93 are 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 DC bias circuit one 91, DC bias circuit two 92, and DC bias circuit four 94 are provided on the third layer of metal 31. The DC bias circuit three 93 and the tunable artificial surface plasmon unit 5 are located on the same first metal layer 11, and the DC bias circuit one 91, the DC bias circuit two 92, and the DC bias circuit four 94 are located on the third metal layer 31, which effectively avoids 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 a 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 and 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 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.

[0028] The first group of varactor diodes 71 is used to adjust the upper cut-off 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 via a second group of varactor diodes 72, two of which 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 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.

[0033] The number of tunable artificial surface plasmon units 5 is N, 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 length of the wide side connecting the transition unit 4 with the feeding structure 3 is less than the length of the wide side connecting the transition unit 4 with 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 head and tail ends of the N tunable artificial surface plasmon units 5 are each connected in series with M transition units; wherein M and N are both 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 and band-pass switchable artificial surface plasmon filter comprises 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 metal layer 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 metal layer 11. Transition units 4 and feeding structures 3 are symmetrically connected at both ends of the tunable artificial surface plasmon unit 5, wherein there are four transition units 4 in total. 5 has two transition units 4 connected in series at the starting end and the tail end respectively; 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 the upper and lower sides of the first metal layer 11 are respectively provided with DC bias circuit three 93; the reverse side of the second dielectric plate 2 is provided with a third metal layer 31, and the third metal layer 31 is provided with a DC bias circuit one 91, a DC bias circuit two 92, and a DC bias circuit four 94, which can provide bias voltages V1, V2, and V4, respectively.

[0039] The feeding structure 3 is a microstrip line with a characteristic impedance of 50 ohms. The left and right feeding structures 3 are both welded with SMA connectors for connecting 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 a microstrip line with a width of 5.62 mm, 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, and the metal branch 51 is a U-shaped structure bent inward, with a total length of 9 mm and a width of 0.7 mm; a tunable artificial surface plasmon unit 5 includes four metal branches 51, which are symmetrically arranged up and down and left and right; the dispersion characteristics of the artificial surface plasmon waveguide can be adjusted 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 first, third, fifth, and seventh tunable artificial surface plasmon units 5 are connected to the DC bias circuit three 93 of the same layer through the DC blocking inductor 81, and the bias voltage provided is V3; the metal branches 5 in the second, fourth, and sixth 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, 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 dispersion 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 by two parallel second groups of varactor diodes 72, the direction of the second group 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 group of varactor diodes 72 is turned on, and the filter provided in this embodiment is in a low-pass state. At the same time, the capacitance value of the first group 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, 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 group 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 group of diodes 72 show different capacitance values, so that the bandpass filter presents different lower cutoff frequencies. Figure 6 As shown in FIG. 1 , when the capacitance value of the second group 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 group 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 with 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 respectively provided on the upper and lower sides of the first layer of metal (11), and a third layer of metal (31) is provided on the back surface 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) comprises 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, two sides of which 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 (55) comprises four metal branches (51) which are symmetrically arranged vertically and horizontally; The first group of varactor diodes (71) is used to adjust the upper cut-off frequency of the band-pass and low-pass 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) via 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) via 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).

2. The active adjustable 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 length of the wide side connecting the transition unit (4) and the feeding structure (3) is less than the length of the wide side connecting the transition unit (4) and 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 direct current bias voltage, thereby changing the upper cut-off frequency.

3. An active adjustable low-pass and band-pass switchable artificial surface plasmon filter according to claim 1 or 2, characterized in that: 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 and different reverse bias voltages of the second group of variable capacitance diodes (72), the switching of low-pass and band-pass filters and the adjustment of the lower cut-off frequency of the band-pass filter are achieved.

4. 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.

5. The active adjustable 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.

6. The active adjustable low-pass and band-pass switchable artificial surface plasmon filter according to claim 3, characterized in that: The distance between the two second groups of varactors (72) connected in parallel is 4 mm.

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