CN110718731B

CN110718731B - Artificial surface plasmon transmission line excitation device based on microstrip line interface

Info

Publication number: CN110718731B
Application number: CN201910862375.1A
Authority: CN
Inventors: 崔铁军; 闫瑞婷; 张浩驰
Original assignee: Southeast University
Current assignee: Southeast University
Priority date: 2019-09-12
Filing date: 2019-09-12
Publication date: 2021-10-19
Anticipated expiration: 2039-09-12
Also published as: CN110718731A

Abstract

The invention discloses an artificial surface plasmon transmission line excitation device based on a microstrip line interface, which is characterized by comprising a metal ground, wherein a medium substrate is arranged above the metal ground, a metal strip is arranged on the medium substrate, one end of the metal strip is provided with a rectangular groove with gradually changed depth, and asymmetric exponential metal flaring ground structures with different curvatures are arranged on the lower metal ground corresponding to the two sides of the metal strip. The artificial surface plasmon excitation device has the characteristics of high efficiency, simple design, compact structure, easiness in processing and the like, is strong in universality and easy to transplant, is suitable for other single-conductor artificial surface plasmon transmission lines with grooves on one side or two sides, and has wide application prospect in the field of novel microwave integrated circuits and devices.

Description

Artificial surface plasmon transmission line excitation device based on microstrip line interface

Technical Field

The invention relates to artificial electromagnetism, in particular to an artificial surface plasmon transmission line excitation device based on a microstrip line interface.

Background

Surface plasmons (SPPs) are surface electromagnetic waves that exist at the interface of two media with opposite dielectric constants, as derived from maxwell's equations. In the visible light frequency band, metal has negative dielectric constant, the free electrons in the metal are in plasma state, and the dielectric constant of air layer is positive value, so that surface plasmon exists on the surface of metal in natural state. Surface plasmons have several unique properties: significant field enhancement effect, strong field confinement capability, and sub-wavelength effect. However, at lower frequencies, such as in the microwave range, metals behave as ideal electrical conductors rather than as plasmas, so that no natural surface plasmons are present at low frequencies.

The artificial surface plasma can be excited in a frequency band below the visible light frequency by applying the concept of the novel artificial electromagnetic material. Research has proved that an ultrathin single-conductor grooved structure can support surface plasmon transmission similar to the visible light frequency band in the microwave and terahertz wave bands, and is called artificial surface plasmon. However, the artificial surface plasmon transmission based on the theory faces a big problem, namely how to perfectly link with the existing double-conductor structure system on a single-conductor structure, realize high-efficiency artificial surface plasmon excitation and make the structure simple and compact, thereby keeping the characteristics of the artificial surface plasmon unchanged.

Disclosure of Invention

The purpose of the invention is as follows: the invention aims to provide an artificial surface plasmon transmission line excitation device based on a microstrip line interface, which solves the problems of poor connection and complex structure of the existing double-conductor structure.

The technical scheme is as follows: the artificial surface plasmon transmission line excitation device based on the microstrip line interface comprises a metal ground, wherein a medium substrate is arranged above the metal ground, a metal strip is arranged on the medium substrate, one end of the metal strip is provided with a rectangular groove with gradually changed depth, and asymmetric exponential metal flaring ground structures with different curvatures are arranged on the metal ground below the metal strip and correspond to the two sides of the metal strip.

Wherein the metal flared structure extends upward and downward, respectively, with the metal strip as a boundary.

The metal strips are arranged longitudinally along the dielectric substrate.

The rectangular groove is formed by etching on the metal strip.

The thickness of the medium substrate is 0.254-1.524 mm.

In order to improve the transmission efficiency, the loss tangent value of the dielectric substrate is less than 0.04.

Has the advantages that: the invention uses the microstrip as a feed interface, and realizes the high-efficiency excitation of the double-conductor transmission line structure with universality to the artificial surface plasmon single-conductor transmission line by designing the feed device. The excitation device has the advantages of simple and compact structure, convenient processing, low cost and light weight. The traditional microstrip excitation device needs to perform complex conversion between a microstrip-coplanar waveguide-artificial surface plasmon transmission line or needs large-area metal ground connection, so that smooth connection between a double conductor and a single conductor cannot be really realized. The artificial surface plasmon transmission line excitation device directly excited by the microstrip line provided by the invention has a relatively simple manufacturing process, not only saves the manufacturing cost, but also avoids the processing error caused by complex process steps. The invention has the characteristic of broadband high efficiency. The C wave band and the X wave band are covered in the frequency band from 4GHz to 12GHz, and the transmission requirements of equipment such as satellite communication and the like can be met. The insertion loss of the single-port excitation device of the artificial surface plasmon transmission line is 1dB, and the broadband high-efficiency characteristic of the single-port excitation device is displayed. The dielectric substrate adopted by the invention is very thin, so that the whole array has the characteristic of being light and thin, and can be widely applied to a plurality of projects with limited weight. The excitation device adopted by the invention is simple in design, is convenient to transplant to different types of single-conductor artificial surface plasmon transmission lines with different sizes as the excitation device, and is convenient to optimize structural parameters to realize efficient excitation.

Drawings

FIG. 1 is a schematic structural view of the present invention;

fig. 2 (a) is a schematic diagram of the structure of an artificial surface plasmon transmission line unit to which the present invention is applied, and (b) is a dispersion curve diagram for different groove depths d;

FIG. 3 is a full wave simulation and experimental test scattering parameters of a dual-port artificial surface plasmon transmission line fed by an excitation device according to the present invention;

fig. 4 is a schematic diagram of near-field simulation of electric fields on an artificial surface plasmon transmission line fed by using the excitation device provided by the invention at different frequencies.

Detailed Description

The invention is further described below with reference to the accompanying drawings.

As shown in fig. 1, the artificial surface plasmon transmission line excitation device based on the microstrip line interface comprises a metal ground 6, a dielectric substrate 7 is arranged above the metal ground 6, a metal strip 2 is arranged on the dielectric substrate 7, a rectangular groove 3 with gradually changing depth is arranged at one end of the metal strip, the rectangular groove arrangement mode is the same as that of the artificial surface plasmon unit structure, the groove depth gradually increases in sequence according to gradient until the depth of the last groove is the same as that of the artificial surface plasmon unit structure, asymmetric index metal flaring ground structures with different curvatures are arranged on the lower metal ground 6 corresponding to two sides of the metal strip 2, the asymmetric index metal flaring ground structures comprise a first index metal flaring ground structure 4 and a second index metal flaring ground structure 5, the asymmetric index metal flaring ground structures with different curvatures are distributed on two sides of the metal strip as a boundary and respectively extend upwards, the first index type metal flaring ground structure 4 is positioned on one side above the upper groove of the metal strip, and the second index type metal flaring ground structure 5 is positioned on one side below the upper groove of the metal strip and is in metal connection with the microstrip line on the lower layer of the dielectric substrate. The first exponential metal flared ground structure 4 has a large curvature and a small occupied area because the metal strip has strong field binding capability near the artificial surface plasmon transmission line on one side of the groove. The second exponential metal flaring ground structure 5 is a flaring ground structure at one side far away from the groove in the metal strip, and because the field constraint of the artificial surface plasmon transmission line part corresponding to the non-groove side is relatively weak, the curvature is small, and the occupied area is relatively large. Wherein the thickness of the dielectric substrate is 0.254-1.524mm, and the loss tangent value of the dielectric substrate is less than 0.04.

The upper layer conduction band of the microstrip line dielectric substrate is connected with the groove with gradually changed depth, and the lower layer metal ground is split from the conduction band and is respectively expanded along the longitudinal direction of the transmission line according to different exponential forms to form an asymmetric expanded ground structure, so that the efficient excitation of the single-conductor artificial surface plasmon transmission line by utilizing the microstrip line in a microwave frequency band is realized. According to the intrinsic mode simulation, the dispersion characteristic of the metal structure of the etched rectangular groove printed on the ultrathin medium substrate is very obvious, and the dispersion degree is increased along with the increase of the depth of the groove, so that the wave vector matching between the microstrip and the artificial surface plasmon transmission line unit structure can be realized by utilizing the groove with gradually changed depth. The asymmetric flaring ground structure realizes impedance matching and field type conversion between the microstrip line and the artificial surface plasmon, the asymmetric structure is suitable for the artificial surface plasmon transmission line excitation device with unilateral grooving, and for the symmetric artificial surface plasmon transmission line with bilateral grooving, the flaring ground structure is designed to be symmetric, namely, the flaring ground curvatures are the same, so that efficient artificial surface plasmon excitation can be realized. The results of numerical simulation and experimental test show the broadband and high-efficiency characteristics of the invention.

Fig. 2 is a schematic diagram of the structure of an artificial surface plasmon transmission line unit applied to the present invention and a dispersion curve diagram for different groove depths d. The unit structure is composed of metal strip etched rectangular grooves printed on a medium substrate, wherein the length of a unit period is p which is 3mm, the width of the unit period is h which is 3.6mm, the groove depth is d which is 3mm, the groove width is a which is 1.5mm, the medium substrate is Rogers RT5880, and the thickness of the groove is ts which is 0.508 mm. The dispersion curves corresponding to the unit structures with different groove depths d, which are obtained by an eigenmode solver in a commercial software CST microwave working chamber, show that the depth gradient grooves can be used for connecting the microstrip line conduction band and the artificial surface plasmon transmission line to realize wave vector matching.

Fig. 3 is a graph comparing scattering parameters from full wave numerical simulations and experimental tests of the two-port transmission line including the feeder shown in fig. 1. The numerical simulation and experimental test results are basically consistent, wherein the transmission coefficient S21 can reach-1.5 dB in the pass band from 4GHz to 12GHz, and the reflection coefficient S11 is lower than-10 dB, which shows that the insertion loss of the artificial surface plasmon transmission line including the feeding device is maintained within 1dB in the broadband range from 4GHz to 12GHz, and the broadband and high-efficiency characteristics of the invention are verified.

FIG. 4 is an electric field near-field distribution diagram obtained by numerical simulation software for the two-port artificial surface plasmon transmission line shown in FIG. 1 at 4GHz, 8GHz and 12 GHz. The near field distribution diagram can obviously observe the field binding effect and good transmission performance of the artificial surface plasmon, and the phenomenon of field pattern disturbance exists at the

flaring ground structures

4 and 5 due to the certain radiation effect of the flaring ground structure of the feeding device, but the overall excitation efficiency is still kept above 89.1%. The field patterns of the feed devices and the artificial surface plasmon transmission line at other frequency points in the passband are smoothly converted, the excitation efficiency is high, and the requirements of the bandwidth and the efficiency of a communication system can be met.

Claims

1. The artificial surface plasmon transmission line excitation device based on the microstrip line interface is characterized by comprising a metal ground (6), wherein a dielectric substrate (7) is arranged above the metal ground (6), a metal strip (2) is arranged on the dielectric substrate (7), one end of the metal strip (2) is provided with a rectangular groove (3) with gradually changed depth, asymmetric index type metal flaring ground structures with different curvatures are arranged on the metal ground below the metal strip (2) corresponding to the two sides, and the metal flaring ground structures respectively extend upwards and downwards by taking the metal strip as a boundary.

2. The microstrip line interface-based artificial surface plasmon transmission line excitation device according to claim 1, characterized in that said metal strip (2) is arranged longitudinally along the dielectric substrate (7).

3. The microstrip line interface-based artificial surface plasmon transmission line excitation device according to claim 1, wherein the rectangular groove is formed by etching on a metal strip.

4. The microstrip line interface-based artificial surface plasmon transmission line excitation device according to claim 1, wherein the thickness of the dielectric substrate (7) is 0.254-1.524 mm.

5. The microstrip line interface-based artificial surface plasmon transmission line excitation device according to claim 1, wherein the dielectric substrate (7) has a loss tangent value of less than 0.04.