A Design of RFID Antenna based on Left—hand Material

ZHANG Yu

【Abstract】Square-shaped Split-ring resonator （SRR） left-hand Material（LHM） is proposed in Radio frequency band and S parameter extraction method was used to extract the effective permittivity and permittivity are all negative， hence verifying the nature of its left-hand properties. LHM is put on to dielectric layer of the center frequency of 920 MHZ microstrip patch antenna with 50 Ω coaxial feed. Then the left-hand microstrip patch antenna and conventional antenna are compared， finding that return loss S11 down from - 30 dB to -60 dB.

【Key words】left-hand material； S parameter；. microstrip patch antenna

Introduction

In 1968， Veselago puts forward the concept of LHM for the first time. In 1999， Pendry proposed a LHM arranged by metal rods arrays and metal resonance rings. Then it is defined as “a non natural media has properties of natural media do not have”.It has negative permittivity（ε）and negative permeability （μ）simultaneously. It can be used to improve microwave and optical frequency device performance， such as optical fiber and waveguide， also used in electromagnetic wave stealth， manufacturing military antenna， etc. In 2000， Dr. Smith make a copper wire array and the metal copper ring resonant together， surprising to find a LHM with negative ε and negative μ simultaneously. Thus we can conclude the thought of a way of making LHM， that is make electric resonance material and magnetic resonance material together， and then use the laboratory methods， numerical methods and software simulation methods to prove that the composite material has negative ε and negative μ simultaneously， so can we determine whether material is LHM.

Square-shaped LHM

30 x 20mm2 SRR is placed on 1 mm Thickness FR4 epoxy resin ， SRR width is 1 mm， SRR gap is 1 mm， SRR opening size is 2 mm， SRR thickness is 0.02 mm. put it Vertically in the rectangular waveguide （247.64 x 123.82 was the central）， which top and bottom is set as the ideal electrical boundary （PEC）， the former and later is set as the ideal magnetic boundary （PMC）.By the theory way of S parameter extraction formula， we can calculate equivalent ε and equivalentμ. Then use S parameter extraction computation formula imported into MATLAB software. After its programming， we can get the equivalent ε and equivalentμ，refractive index n， impedance diagram z.

It shows from S21 curve in figure 1， frequency from 0.87 to 1.05 GHz phase mutation lead to the band having the existence of the left-pass-band. We can see from figure 2， 0.8 to 1.2 GHz of impedance real part is positive， the refractive index imaginary part are negative， which all are LHM properties. It can be seen from figure3， 0.8-1.02 GHz ε and ? are negative. So we can conclude that in from 0.8 to 1.02 GHz frequencies， the square-shaped SRR is in the nature of LHM properties.

1. loading LHM of microstrip patch antenna

Antenna is composed of the thickness of 1.6 mm FR4 epoxy resin board as dielectric layer， with 50 Ω coaxial feed， which relative dielectric constant is 4.4. Length is along with X axis and width is along with Y axis， LHM is along the lower left edge of the dielectric layer.

2. Conclusion

In this paper， Square-shaped SRR is embedded in the dielectric layer， not as a whole cladding， realizing negative permittivity and negative permeability in microwave band. Compared with not joining LHM， S11 can decrease from - 30 dB down to -60 dB. Pattern in H plane antenna gain is pretty， When VSWR is less than 2， the bandwidth is 25 dB， which can improve the directivity， increase the bandwidth.

References：

[1]J B Pendry，A J Holden，D J Robbins，W J Stewart.Magnetism from conductors andenhanced nonlinear phenomena[J].IEEETrans Microw Theory Tech，1999，47（11）：2075-2084.

[2]D R Smith，W J Padilla，D C Vier，et al.Composite medium with simultaneously negative permeability and permittivity[J].Physical Review Letters，2000，84（18）：4184-4187.

作者簡介：張玉（1990-），女，漢族，四川大英人，研究生，光電集成和射頻集成電路設計。