A diplexer based on equivalent localized surface plasmons

Abstract

The application discloses a diplexer based on equivalent local mode surface plasmons, which is characterized by the following steps: parallelly arranging rectangular resonators with different lengths based on equivalent local mode surface plasmons, designing two band-pass filters with different central frequencies, and then connecting the two band-pass filters through T-shaped joints respectively to form a diplexer based on equivalent local mode surface plasmon structure. For different central frequencies, the length of the connection part of the T-shaped joint and the band-pass filter can be adjusted to meet the isolation requirement of two passbands, thereby reducing the complexity of the design of a traditional diplexer and having wide applicability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of microwave technology, and particularly relates to a diplexer based on equivalent local surface plasmons. BACKGROUND

[0002] The research of spoof surface plasmon polaritons (SSPPs) started from the concept of SSPPs proposed by Professor J.B. Pendry of Imperial College in the UK in 2004. By etching periodic subwavelength holes on the surface of metal, the equivalent plasma frequency of the metal is reduced, and the research field of surface plasmons is expanded. In 2005, Professor Hibbin experimentally verified the existence of SSPPs in the microwave band, providing a basis for the application of SPPs in low-frequency bands. In 2006, Maier and Garcia-Vidal et al. extended the concept of SSPPs to a three-dimensional model, and theoretically proved that an ideal wire etched with subwavelength periodic ring grooves can also transmit SSPPs, realizing subwavelength confinement and energy focusing of the field. In order to make the three-dimensional plasmonic waveguide planar and small, and to be applied to microwave integrated circuits, Professor Cui Tiejun of Southeast University first proposed a conformal surface plasmon (CSP) in 2013, which realized strong confinement and efficient transmission of signals on an ultrathin plasmonic waveguide with arbitrary bending. Subsequently, they also proposed related frequency dividers and resonators. Professor Feng Yijun of Nanjing University analyzed the generation conditions, dispersion and field distribution characteristics of high-order modes of CSPs, and proposed a microwave plasmonic directional coupler and frequency divider based on CSPs. In 2014, Professor Li Tu of Nanjing University of Aeronautics and Astronautics proposed a composite ultrathin plasmonic waveguide structure containing symmetric teeth and a central hole, which can realize efficient transmission of multi-channel signals. Subsequently, they proposed a theoretical model of SSPPs based on high-contrast grating (HCG) structures, and carried out experimental verification work in the microwave band.

[0003] In the aspect of localized spoof surface plasmons (LSSPs), in 2012, Professor Garcia-Vidal first proposed a model of LSSPs. In 2013, Professor Cui Tiejun first experimentally realized an ultrathin LSSPs structure, which can produce multi-mode resonance phenomenon at the microwave frequency band, and the resonance characteristics are related to the surrounding medium characteristics and geometric structure, and can be used for microwave and terahertz band sensors. In 2013, Yang J.J. et al. of Yunnan University proposed an artificial surface echo wall mode sensor. In 2014, Huidobro P.A. et al. found a magnetic artificial localized surface plasmon resonance phenomenon, which coexists with the electric LSSPs. In the same year, Professor Li Tu's research group proposed a multi-frequency resonance model of LSSPs and a slot-in-cavity LSSPs model and a multi-frequency resonance model.

[0004] In the aspect of waveguide mode dispersion induced equivalent surface plasmon polaritons (ESPPs), in 2016, Professor N. Engheta of the University of Pennsylvania first observed a variety of plasmonic phenomena in the waveguide, including SPPs, LSPs, invisibility cloak, tunneling effect, etc. by placing periodic metal wires at the interface of two ordinary dielectric. But this work only observed the related phenomena through simulation, and did not explain the physical mechanism. In 2017, Professor Li Tu's research group established a theoretical model of mode dispersion induced equivalent surface plasmon polaritons, revealed the dispersion and transmission characteristics of ESPPs, and first experimentally verified the existence of ESPPs at the interface of two ordinary dielectric materials. Through the waveguide port and double-layer substrate integrated waveguide, efficient excitation and low-loss transmission of ESPPs were realized. In 2018, they studied the dispersion model and transmission characteristics of ESPPs in equivalent insulator-metal-insulator (IMI) and equivalent metal-insulator-metal (MIM) structures. The results show that the ESPPs in this multilayer system can be decomposed into odd and even modes due to the strong coupling of the structure, and its dispersion characteristics are very similar to the real SPPs in the IMI and MIM structures in the optical band. This work lays the foundation for the application of ESPPs in multilayer systems. In 2019, the resonance of equivalent localized surface plasmons (ELSPs) was first realized experimentally at the interface of two dielectric materials with positive permittivity. A physical model of structure dispersion induced equivalent localized surface plasmons was established, a scattering cross-section equation based on two-dimensional equivalent localized surface plasmons structure was derived, the resonance mechanism of equivalent localized surface plasmons was revealed, and it was verified by numerical simulation and experiment, which expanded a new research direction for LSPs. SUMMARY

[0005] The application applies the theory of structure dispersion induced equivalent localized surface plasmons (ELSPs), and two bandpass filters with different center frequencies are composed of equivalent localized surface plasmon resonators, and then a T-junction is connected to realize a small, planar and high-performance diplexer.

[0006] The technical scheme applied in the application is as follows:

[0007] The application discloses a diplexer based on an equivalent local area type surface plasmon structure, characterized by comprising a medium substrate, a T-shaped junction arranged on the front surface of the medium substrate, a first band-pass filter and a second band-pass filter; the first band-pass filter is arranged on the upper half of the medium substrate, the input end of the first band-pass filter is connected with an output end of the T-shaped junction, and the output end of the first band-pass filter is connected with the input end of a first microstrip line; the second band-pass filter is arranged on the lower half of the medium substrate, the input end of the second band-pass filter is connected with another output end of the T-shaped junction, and the output end of the second band-pass filter is connected with the input end of a second microstrip line.

[0008] The first band-pass filter is composed of a plurality of cuboid resonators with a first length arranged in parallel with each other, one end of the cuboid resonator with the first length is short-circuited, and the other end of the cuboid resonators located at the left and right edges of the first band-pass filter is respectively connected with an output end of the T-shaped junction and the input end of the first microstrip line.

[0009] The second band-pass filter is composed of a plurality of cuboid resonators with a second length arranged in parallel with each other, one end of the cuboid resonator with the second length is short-circuited, and the other end of the cuboid resonators located at the left and right edges of the second band-pass filter is respectively connected with another output end of the T-shaped junction and the output end of the second microstrip line.

[0010] The opposite surfaces of the cuboid resonators in the first band-pass filter and the cuboid resonators in the second band-pass filter are open surfaces.

[0011] Preferably, the cuboid resonators are made of high dielectric constant ceramic materials, and the short-circuit surface, the upper surface and the lower surface of the cuboid resonator are respectively plated with silver.

[0012] Preferably, each group of cuboid resonators comprises three cuboid resonators, and the length of the cuboid resonator is determined by the center frequency index of the corresponding band-pass filter.

[0013] Preferably, the length of the part of the T-shaped junction connected with the first band-pass filter is 1 / 4 of the wavelength of the second band-pass filter, the length of the part of the T-shaped junction connected with the second band-pass filter is 1 / 4 of the wavelength of the first band-pass filter, and each band-pass filter is open at the center frequency of the other band-pass filter.

[0014] Preferably, the part of the T-shaped junction connected with the first band-pass filter and the second band-pass filter is bent for multiple times and then connected with the first band-pass filter and the second band-pass filter.

[0015] Preferably, the cuboid resonator is a 1 / 4 wavelength resonator.

[0016] The application has the following beneficial effects:

[0017] The application utilizes the parallel placement of rectangular resonators with different lengths based on equivalent localized surface plasmons, designs two bandpass filters with different center frequencies, and then connects the two bandpass filters through T-junctions respectively to form a diplexer based on equivalent localized surface plasmon structure, and by adjusting the length of the T-junction and the bandpass filter connection part, the isolation requirement of the two passbands can be met, the complexity of the traditional diplexer design is reduced, and the application has wide applicability.

[0018] The diplexer based on equivalent localized surface plasmon structure of the application can be applied in the 5G application frequency band, the center frequencies of the two bandpass filters are adjusted to the required frequency points in the design index by adjusting the length of the cuboid resonator, the coupling coefficient is adjusted by adjusting the distance between the cuboid resonators, and the isolation of the diplexer is optimized by adjusting the length of the T-junction and the bandpass filter connection part, thereby improving the product performance. The diplexer based on equivalent localized surface plasmon structure of the application has simple structure and is easy to manufacture. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is a structure schematic diagram of the diplexer based on equivalent localized surface plasmon of example one.

[0020] Figure 2 It is a structure schematic diagram of the first and second bandpass filters of example one.

[0021] Figure 3 It is a structure schematic diagram of the diplexer based on equivalent localized surface plasmon of example two.

[0022] Figure 4 It is a principle diagram of the diplexer based on equivalent localized surface plasmon of example two.

[0023] Figure 5 It is a structure and performance schematic diagram of the bandpass filter of example two; wherein (a) shows the structure of the bandpass filter, (b) shows the structure of the bandpass filter, (c) shows the curve of the coupling coefficient changing with the distance s between the resonators, and (d) shows the curve of the quality factor Q value changing with the position d of the microstrip feed.

[0024] Figure 6 It is an S parameter curve of the bandpass filter of example two.

[0025] Figure 7 It is an S parameter curve of the diplexer based on equivalent localized surface plasmon of example two. DETAILED DESCRIPTION

[0026] The specific embodiments of the application will be described in detail below with reference to the accompanying drawings.

[0027] Example 1

[0028] This embodiment provides a duplexer based on an equivalent localized surface plasmon structure, such as... Figure 1 As shown, the system includes: a high-frequency dielectric substrate 1, and a T-junction 2, a first bandpass filter 3, and a second bandpass filter 4 disposed on the front side of the dielectric substrate 1. A copper layer is plated on the back side of the high-frequency dielectric substrate 1 as a ground plane, which is connected to a microstrip line on the front side of the dielectric substrate via a port. The first bandpass filter 3 is disposed in the upper half of the dielectric substrate 1, with its input terminal connected to one output terminal of the T-junction 2 and its output terminal connected to the input terminal of the first microstrip line 5. The second bandpass filter 4 is disposed in the lower half of the dielectric substrate, with its input terminal connected to the other output terminal of the T-junction 2 and its output terminal connected to the input terminal of the second microstrip line 6.

[0029] like Figure 2 The first bandpass filter 3 consists of a set of three parallel cuboid resonators 7 with a first length of 11, the length direction of which is perpendicular to the wave propagation direction. One end of each cuboid resonator 7 with a first length of 11 is short-circuited, and the other ends of the cuboid resonators located on the left and right edges of the first bandpass filter 3 are respectively connected to one output terminal of the T-junction 2 and the input terminal of the first microstrip line 5. The second bandpass filter 4 consists of a set of three parallel cuboid resonators 7 with a second length of 12, the length direction of which is perpendicular to the wave propagation direction. One end of each cuboid resonator 7 with a second length of 12 is short-circuited, and the other ends of the cuboid resonators located on the left and right edges of the second bandpass filter 4 are respectively connected to the other output terminal of the T-junction 2 and the input terminal of the second microstrip line 6. The faces of the cuboid resonators in the first bandpass filter 3 and the second bandpass filter 4 are open surfaces.

[0030] In this embodiment, the cuboid resonator 7 is made of a high dielectric constant ceramic material. The short-circuit surface, upper surface, and lower surface of the cuboid resonator are plated with silver.

[0031] The length of the cuboid resonator 7 in this embodiment is determined by the passband center frequency index of the corresponding bandpass filter.

[0032] In this embodiment, the portion of the T-junction connected to the first bandpass filter 3 has a length that is 1 / 4 of the wavelength of the second bandpass filter 4; the portion of the T-junction connected to the second bandpass filter 4 has a length that is 1 / 4 of the wavelength of the first bandpass filter 3; each bandpass filter is open-circuited at the center frequency of the other bandpass filter.

[0033] The rectangular resonator of the embodiment adopts a 1 / 4 wavelength resonator, the resonant mode of which is not sensitive to the cross-sectional shape, and at the same frequency, the resonator length is half of that of a half wavelength resonator, the size is smaller, the planarization is better, and the integration is easier.

[0034] The embodiment is based on an equivalent local mode surface plasmon, and two bandpass filters with different center frequencies are formed by rectangular resonators with different lengths based on the equivalent local mode surface plasmon, and then connected through a T-junction to form a diplexer with high isolation, low insertion loss and high Q value. By adjusting the length of the part where the T-junction is connected with the bandpass filter, a small, planar and high-performance diplexer can be easily realized.

[0035] Embodiment two

[0036] The embodiment provides a diplexer based on an equivalent local mode surface plasmon structure, as shown in Figure 3 The basic structure of the diplexer is the same as that in embodiment one, but in the embodiment, the part where the T-junction connects the first bandpass filter and the second bandpass filter is bent multiple times before being connected with the first bandpass filter and the second bandpass filter. The use of bent transmission lines can make the diplexer structure more compact, reduce the occupied area, and thus reduce the overall size of the device.

[0037] The rectangular resonator of the embodiment adopts a 1 / 4 wavelength resonator, the resonant mode of which is not sensitive to the cross-sectional shape, and at the same frequency, the resonator length is half of that of a half wavelength resonator, the size is smaller, the planarization is better, and the integration is easier.

[0038] The diplexer of the embodiment has passbands at two center frequencies of 2.6 GHz and 3.1 GHz, and by adjusting the length of the transmission line of the part where the T-junction is connected with the bandpass filter, i.e. Figure 3 the length of (I m1 +I m11 +I m12 +I m13 ) and the length of (I m2 +I m21 +l m22 +I m23 ), the interaction between the two filters can be minimized, thereby reducing the influence on the return loss and insertion loss of the filters, and realizing a diplexer design with high isolation, low insertion loss and high Q value.

[0039] The approximate analytical formula of the resonant frequency fa of the quarter wavelength rectangular resonator of the embodiment is as follows:

[0040]

[0041] where c represents the speed of light in vacuum, and εr is the relative dielectric constant of the medium, and 1 is the length of the resonator. As can be seen from equation (1), the resonant frequency of the resonator dipole mode based on the equivalent localized surface plasmon is independent of the radius r.

[0042] As Figure 4 shown, the connection part of the T-junction and the band-pass filter is equivalent to introducing a microstrip transmission line at the input end of the band-pass filter. By adjusting the length of the microstrip transmission line, the phase of the reflection coefficient and can be changed, so that each band-pass filter is open-circuited at the center frequency of the other band-pass filter, i.e., at the center frequencies f 01 and f 02 , so that the reflection coefficients and are equal to 0°. After parameter optimization, a 50Ω characteristic impedance microstrip transmission line with a length of λ g2 / 4 is connected in series before and after the first band-pass filter (filter 1), and a 50Ω characteristic impedance microstrip transmission line with a length of λ g1 / 4 is connected in series before and after the second band-pass filter (filter 2), and the design effect is as shown in Figure 7 .

[0043] The specific design process of the embodiment is as follows:

[0044] Design index:

[0045] (1) Center frequency: 3.1 GHz

[0046] (2) Relative bandwidth: 7.7%;

[0047] (3) Return loss > 20 dB;

[0048] (4) Insertion loss < 1 dB.

[0049] A three-order Chebyshev low-pass filter prototype with a passband ripple of 0.1 dB is selected. When the normalized low-pass cutoff frequency Ωc = 1, the low-pass prototype parameters are g0 = 1, g1 = 1.0316, g2 = 1.1474, g3 = 1.0316, and g4 = 1. The coupling coefficients M 12 and M 23 and the external quality factor Q e are determined as

[0050]

[0051]

[0052] where FBW is the relative bandwidth. The relative dielectric constant is selected as 12.3, and the loss tangent is selected as 2.36 x 10-4 ceramic material of the application as the material of the cuboid resonator with a cross section of 2mm*2mm. Silver is plated on the upper and lower surfaces of the dielectric and the short-circuit surface. The duplexer structure adopts a microstrip feed excitation mode, and the cuboid resonators are arranged in parallel groups on the substrate. The substrate is made of Rogers RT5880, with a thickness of 0.508mm, a size of 35*33mm, and a relative dielectric constant of 2.2. According to equation (1), the length of the cuboid resonator based on the equivalent localized surface plasmon is 9.5mm.

[0053] The coupling coefficient M between resonators i and j is found by using the eigenmode solver in CST STUDIO ij , where M can be extracted from the following relationship ij :

[0054]

[0055] where fp1 and fp2 represent the two resonance frequencies of two parallel coupled resonators based on the equivalent localized surface plasmon. Using the eigenmode solver in CST STUDIO, the variation curve of the external quality factor (as shown in (d) of Figure 5 ) is found, and the variation of the feed position (denoted by d) is found, where Qe can be extracted by the following way:

[0056]

[0057] where ω0 is the resonance angular frequency, should be determined by the absolute bandwidth corresponding to the actual phase shift of 90° in positive and negative directions at the resonance frequency ω0. By fitting the value in equation (2) to (c) in Figure 5 , the initial value of s = 1.7mm is obtained, and by fitting the value in equation (3) to (d) in Figure 5 , the value of d = 1.7mm is obtained.

[0058] The S parameters of the filter are optimized by fine-tuning s and d. Finally, the expected design indicators are achieved, and the S parameter simulation result is shown in Figure 6 , with a center frequency of 3.1GHz, a relative bandwidth of 7.7%, and a return loss greater than 23dB.

[0059] In other embodiments, the substrate substrate is not limited to the Rogers RT5880 plate, as long as it can well support the resonator structure, is not easy to deform, has a relatively low relative dielectric constant value, and has a small effect on the width of the microstrip feed line.

[0060] In other embodiments, the cuboid resonator structure cross section is not limited to square due to the insensitivity of the equivalent localized surface plasmon based resonator structure to cross section variations.

[0061] In other embodiments, the resonator length is also not limited to 9.5 mm, and can be adjusted according to the design index of the center frequency.

[0062] The above embodiments only illustrate the technical ideas of the present application, and cannot limit the protection scope of the present application. Any modification made according to the technical ideas of the present application on the basis of the technical solutions falls within the protection scope of the present application.

Claims

1. A diplexer based on equivalent localized surface plasmon structure, characterized in that, The application relates to a medium substrate, a T-shaped junction arranged on the front surface of the medium substrate, a first band-pass filter and a second band-pass filter. The first band-pass filter is arranged on the upper half of the medium substrate, the input end of the first band-pass filter is connected with an output end of the T-shaped junction, and the output end of the first band-pass filter is connected with the input end of a first microstrip line; the second band-pass filter is arranged on the lower half of the medium substrate, the input end of the second band-pass filter is connected with another output end of the T-shaped junction, and the output end of the second band-pass filter is connected with the input end of a second microstrip line. The first band-pass filter is composed of a group of paralleled cuboid resonators with a first length, one end of the cuboid resonator with the first length is short-circuited, and the other end of the cuboid resonators located at the left and right edges of the first band-pass filter is respectively connected with an output end of the T-shaped junction and the input end of the first microstrip line. The second band-pass filter is composed of a group of paralleled cuboid resonators with a second length, one end of the cuboid resonator with the second length is short-circuited, and the other end of the cuboid resonators located at the left and right edges of the second band-pass filter is respectively connected with another output end of the T-shaped junction and the output end of the second microstrip line. The opposite surfaces of the cuboid resonators in the first band-pass filter and the second band-pass filter are open surfaces. The cuboid resonators are made of high dielectric constant ceramic materials, and the short-circuit surface, the upper surface and the lower surface of the cuboid resonator are respectively plated with silver. Each group of cuboid resonators comprises three cuboid resonators, and the length of the cuboid resonator is determined by the passband center frequency index of the corresponding band-pass filter.

2. The equivalent localized surface plasmon structure-based diplexer according to claim 1, wherein The length of the part of the T-shaped junction connected with the first band-pass filter is 1 / 4 of the wavelength of the second band-pass filter, the length of the part of the T-shaped junction connected with the second band-pass filter is 1 / 4 of the wavelength of the first band-pass filter, and each band-pass filter is open at the center frequency of the other band-pass filter.

3. The equivalent localized surface plasmon structure-based diplexer according to claim 1, wherein The parts of the T-shaped junction connected with the first band-pass filter and the second band-pass filter are respectively connected with the first band-pass filter and the second band-pass filter after being bent for multiple times.

4. The equivalent localized surface plasmon structure-based diplexer according to claim 1, wherein, The cuboid resonator is a 1 / 4 wavelength resonator.

5. The equivalent localized surface plasmon structure-based diplexer according to claim 1, wherein ​

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