8th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics – Metamaterials 2014 Copenhagen, Denmark, 25-30 August 2014

Compact Novel Coaxial Fed Planar Metamaterial Antenna

Sameer Kumar Sharma1 and Raghvendra Kumar Chaudhary 2

Department of Electronics Engineering, Indian School of Mines, Dhanbad, Dhanbad-826004, INDIA

1sharma.sameer16@gmail.com

Abstract – In this paper, a compact novel coaxial fed planar metamaterial antenna is proposed. The proposed structure shows compact nature having an antenna size of 0.29λo × 0.14λo × 0.02λo and radiating element size of 0.22λo × 0.09λo × 0.02λo with an impedance bandwidth of 118.6 MHz (at centre frequency of 4.32 GHz). The proposed antenna shows excellent monopole-like radiation pattern in H-plane at frequency of 4.32 GHz with low cross polar component in E-plane as well.

I. INTRODUCTION

After 1980’s wireless technology has undergone a lot of modernization which has led to large scale

miniaturization of antennas in order to be used with integrated devices. Planar microstrip antennas for monopole patterns in wireless applications have attracted researchers greatly due to their simple, low cost, and low profile design specifications [1]. But problems with these antennas are either size or frequency of operation. Size of microstrip antenna is about half of guided wavelength λg. If dimensions of such antennas are reduced then they resonate at higher frequency which is also not desirable [1]. Conventional ways such as shorting posts and slots also do not change the dimensions significantly [2, 3]. As a result scientists and researchers are now focusing on the use of MTM’s for reduction in size of such antennas to make them useful in wireless domain [4-9]. MTM’s are defined as artificially made homogenous materials (size < λg/4) which show unusual properties (µ, ε<0) [10].With the use of such MTM’s antenna structures can be made to resonate at lower frequency or result in reduction of size as well. But sometimes there is a trade-off between miniaturization and radiation patterns. [11, 12]

In this paper, a compact planar coaxial fed metamaterial antenna is proposed. Antenna geometry along with simulation results is presented and simulation analysis has been performed by using Ansys high frequency structural simulator (HFSS).

II. ANTENNA GEOMETRY

The antenna is designed on FR4 substrate (with relative permittivity (εr) = 4.4, dielectric loss tangent= 0.025) and dimensions of 20 mm×10 mm×1.6 mm. Fig. 1(a) shows the 3D view while 1(b) depicts top view of the proposed antenna. On the top of substrate digital A type structure is printed with legs forming an interdigital capacitor. A rectangular patch is also printed in the gap region where coaxial feed in centre is provided. Parametric analysis has been performed to obtain optimal antenna design parameters which are listed in Table I.

(a) (b)

Fig. 1. Proposed compact coaxial fed planar metamaterial antenna (a). 3D view (b). top view

978-1-4799-3452-2/14/$31.00 ©2014 IEEE 274

8th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics – Metamaterials 2014 Copenhagen, Denmark, 25-30 August 2014

TABLE I OPTIMAL ANTENNA PARAMETERS

Parameter Lp Wp L W Lr Wr Ls Ts g1 g2 g3 Hs Unit(mm) 15 6 5 4 4.1 2.7 3.25 0.4 1 0.6 1.6 1.6

III. RESULTS AND DISCUSSIONS

Fig. 2. shows the simulated input reflection coefficient (S11) of proposed metamaterial antenna. It is evident

that proposed antenna has a centre frequency of 4.32 GHz and shows input impedance bandwidth of 118.6 MHz below -10dB.

Fig. 2. Simulated input reflection coefficient (S11) of proposed compact coaxial fed planar metamaterial antenna.

(a) (b) Fig. 3. Simulated radiation patterns of proposed compact coaxial fed planar metamaterial antenna in (dB) (a). E-plane at 4.32 GHz (b). H-plane at 4.32 GHz

The simulated normalized co- and cross- polar radiation patterns of proposed compact coaxial fed planar

metamaterial antenna are shown in Fig. 3(a) and 3(b). At 4.32 GHz, H-plane pattern demonstrate monopole-like radiation with low cross polar component going down by 48 dB at 0˚ and 180˚ degree while for E-plane cross polar component is very low around 56 dB at 140˚.

Peak gain profile and radiation pattern are presented in Fig. 4(a) and 4(b) respectively. It is clear that structure

has an average peak gain of approximately 2 dB for the band of 4.258 GHz - 4.377 GHz and radiation efficiency of 87% at centre frequency.

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8th International Congress on Advanced Electromagnetic Materials in Microwaves and Optics – Metamaterials 2014 Copenhagen, Denmark, 25-30 August 2014

(a) (b)

Fig. 4. Simulated profiles of proposed compact coaxial fed planar metamaterial antenna (a). gain profile (b). radiation efficiency profile.

IV. CONCLUSION

A compact novel coaxial fed planar metamaterial antenna has been presented. The structure exhibits similar electrical circuit as that of conventional MTM along with small size. The single-cell metamaterial based antenna has an impedance bandwidth of 118.6 MHz (at centre frequency of 4.32 GHz) and peak gain of 2.03 dB with radiation efficiency of 87%. The proposed antenna structure with an antenna dimensions of 0.29λo × 0.14λo × 0.02λo and radiating element size of 0.22λo × 0.09λo × 0.02λo shows compact size and excellent monopole type radiation pattern in H-plane and very low cross polar component in E-plane. So, proposed antenna shows compact size, excellent radiation patterns with high radiation efficiency, which is suitable for the applications in wireless communication domain.

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