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Microstrip Antenna Incorporated with Left-Handed Metamaterial at 2.7 GHz

M. K. A. Rahim, H. A. Majid, and T. Masri

Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor, MalaysiaEmail: mkamal@fke.utm.my, huda_set@yahoo.com, ithelaha@yahoo.com.my

ABSTRACT: The scope of this project was to design and simulate left-handed metamaterial structure incorporatedwith a single microstrip patch antenna at 2.7 GHz. The combination of the modified square rectangular split ring (SRR)

and the capacitance loaded strip (CLS) was used to obtain the negative value of permeability, and the negativepermittivity, . From the simulation and fabrication done, the gain of the antenna has been increased up to 4 dB. Thishad proven that the LH MTM can enhance the gain of the antenna.

INTRODUCTION

Metamaterials, also known as left-handed metamaterial(LHM) where the permeability and permittivity aresimultaneously negative. LHM is an interesting material to be investigated where this artificial material has several

unique properties such as the backward wave and the focusing effect inside it slab. The history of LHM was startedfrom Veselago [1] when he made a theoretical speculation of this artificial material that exhibit negative permittivityand negative permeability. Thirty four years later, on 2001, Smith made the first prototype structures of LHM [2]. TheLHM is a combination of Split Ring Resonator (SRR) and thin wire (TW). Since the introduction of LHM twelve yearsago, a lot of researcher interested in investigating this artificial material and several of them was using LHM to improvethe properties of the microwave devices such as antenna and filter [3]. Many papers have been published about the

LHM integrated with antennas and their properties have been analyzed. By 2003, researchers had verified that not onlywere these engineered materials possible, but they also could enable "perfect" lenses that were nevertheless flat. Thefocusing affect of LHM made a low gain antenna becomes directive and have an increment of gain [4 and 5].

This paper discussed and analyzed the properties of the LHM and the microstrip antenna with and without the LHMstructure. The designed LHM is a combination of a modified SRR and capacitance loaded strip (CLS). The LHM andantenna were targeted to operate at 2.4 GHz. The negative permittivity and negative permeability of the simulated LHMstructures were presented.

LHM STRUCTURE

The proposed structure for the LHM is a SRR and two CLS as shown in Figure 1. The modified SRR will producemagnetic material-like responses and exhibit the negative permeability and the CLS will produce strong dielectric-likeresponses and exhibit the negative permittivity [6 and 7].

Figure 1: Front view of LHM

LHM PARAMETRIC STUDIES

The simulation of LHM was done using Computer Simulation Technology (CST) software. Perfect magnetic conductor(PMC) boundary condition was set on the front and back faces of the block and perfect electric conductor (PEC)boundary condition was set on the top and bottom of the block. The E- field of the incident wave is polarized along y-

978-1-4244-4396-3/09/$25.00 2009 IEEE

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axis while the H-field of the incident wave is polarized along z-axis. The LHM structure is printed to a FR4 boardwhere the epsilon is 4.7 with the thickness of 1.6 mm. The LHM structure was put inside a vacuum with a dimension of49x17x9.6 mm. The relative permittivity of the FR4 board is 4.7 and its tangential loss is 0.019.

The observation was first done with a structure consist SRR and thin wire as shown in Figure 2. Parametric study wasdone to get a good S11 and S21 that operate at 2.4 GHz. By changing the length of the SRR, the resonant frequency can

be shift to the desired frequency as shown in Figure 3. The width and gap of the SRR are playing a small part onshifting the resonant frequency.

Figure 2: Construction of SRR and TW during simulation

Figure 3: S11 shift due to SRR length vary

The thin wire where then been replaced with two CLS placed at both side of the SRR. The SRR was then beenoptimized to get the S11 and S21 resonate at 2.4 GHz. By changing the length of the SRR, the resonant frequency can beshift to the desired frequency as shown in Figure 4. The CLS was put alone aside. The final structure of the LHMstructure is shown in Figure 1 before and the value of permittivity and permeability for a single cell are shown in Figure

5(a) and 8 cells of LHM are shown in Figure 5(b). The range of the negative permittivity and negative permeability (-and -) for the 8 cell LHM starts from 2.32 GHz to 2.35 GHz and continues from 2.50 GHz to 2.85 GHz.

Figure 4: S11 shift due to structure size vary

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(a) (b)

Figure 5: (a) Value of permittivity and permeability of single cell LHM Figure and (b) Value of permittivity and

permeability of 8 cells LHM

The S-parameters that was obtained from the simulation were then exported to the MathCAD. Nicholson, Ross andWeir (NRW) approach [6] was used to determine the permittivity and permeability of the LHM.

Figure 7 shows the LHM structure integrated with a 2.7 GHz microstrip antenna. The integration between the designed

LHM with a 2.4 GHz microstrip antenna did not give a good results. The structure was simulated using CST. The samematerial of LHM was used for the microstrip antenna and a coaxial feed was used to feed the patch of microstripantenna. The LHM structure was placed in front of the microstrip antenna with a distance of 6.16 mm. The simulatedreturn loss (S11) of the antenna with and without the LHM structure is shown in Figure 8. The simulated radiationpattern of the antenna is shown in Figure 9 and the radiation pattern of the antenna integrated with LHM structures isshown in Figure 10.

Figure 7: Single patch antenna incorporated with LHM structure

Frequency, GHz

1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2

S11,

dB

-35

-30

-25

-20

-15

-10

-5

0

5

Single patch microstrip antenna

LHM with Single patch microstrip antenna Figure 8: Return losses

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Figure 9: Radiation pattern of single patch microstrip antenna

Figure 10: Radiation pattern of single patch microstrip antenna with LHM structure

DISCUSSION

From observation, the length of the SRR is very crucial where the resonance frequency can be altered to what wedesired. The introduction of CLS make the SRR become smaller and it will reduce the size of the structure and thereturn loss better than before. The range of negative value of permittivity and permeability should be close to the

resonance frequency observed from S11. The radiation pattern of microstrip antenna integrated with LHM structure hasan improved gain compared to the gain of the microstrip antenna without LHM structure. An improvement of the gainby 4.5 dB in simulation is obtained when LHM is placed in front of the microstrip antenna. The increment of gain of the

microstrip antenna shows the LHM structure act as a lens where the wave focus in front of the LHM structure. The half-power beam-width (HPBW) of the single patch microstrip antenna with LHM structure is narrower than the HPBW ofthe single patch microstrip antenna. This also shows that LHM can be a focusing device where the beam becomenarrow and the gain increased. However, despite increasing of gain, the side and back lobe was also increased. If theside and back lobe can be reduce, the gain of the microstrip antenna with LHM structure can be further improved.

REFERENCES

[1] Veselago, V. G. 1968, The Electrodynamics of Substances with Simultaneously Negative Value of Permittivityand Permeability, Sov. Phys-Usp., 10, 509-514

[2] B. Szentpali, Metamaterials: A New Concept In Microwave Technique, Telsiks, 2003[3] S. Gil, J. Bonache, J.Garcia-Garcia, F. Falcone, F. Martin, Metamaterials in Microstrip Technology for Filter

Applications, IEEE, 2005[4] Hu Jun, Yan Chun-sheng, Lin Qing-chun, New Patch Antenna with MTM Cover, J Zhejiang University

SCIENCE A 7(1), 89-94, 2006[5] Shah Nawaz Burokur, Mohamed Latrach and Sergre Toutain, Theoritical Investigation of a Circular Patch

Antenna in the Presence of a Left-Handed Mematerial, IEEE Antennas and Wireless Propagation Letters,Vol. 4, 2005

[6] Richard R. Ziolkowski, Double Negative Metamaterial Design, Experiments and Applications, IEEETransactions on Microwave Theory and Techniques, Vol.51, No. 7, July 2003

[7] C. Caloz, T. Itoh, Electromagnetic Metamaterials Transmission Line and Microwave Applications, WileyInterscience, 2005