RESEARCH ARTICLE Gain enhancement of slot antenna using zero-index metamaterial superstrate Tarakeswar Shaw | Deepanjan Bhattacharjee | Debasis Mitra Department of Electronics & Telecommunication Engineering, Indian Institute of Engineering Science and Technology, Shibpur, Howrah, West Bengal 711103, India Correspondence Tarakeswar Shaw, Department of Electronics & Telecommunication Engineering, Indian Institute of Engineering Science and Technology, Shibpur, Howrah, West Bengal 711103, India. Email: tarakeswar.shaw@gmail.com Funding information For research support T. Shaw acknowledges the Visvesvaraya PhD scheme for Electronics & IT research fellowship award and D. Mitra acknowledges the Visvesvaraya Young Faculty research fellowship award, under DeitY, Govt. of India. Abstract This article presents a technique to enhance the broadside gain of a CPW fed slot antenna using a single layer metamaterial (MTM) superstrate. A finite array of 33 3 ring unit cell has been designed on both sides of a dielectric substrate to form the MTM superstrate. The gain enhancement is obtained using the zero-index property of the metamaterial. The broadside gain enhancement for the proposed antenna is 7.4 dB more in comparison to that of the reference slot antenna. The proposed MTM superstrate loaded antenna provides a minimum overall thickness in the context of using ZIM superstrate for gain enhancement of antennas reported in earlier literatures. The overall thickness of the MTM loaded antenna is 0.13k 0 , where k 0 is the free- space wavelength at the resonance frequency of the antenna. Also, a high efficiency of about 93.2% is obtained in this case. The loading of the MTM superstrate pro- duces a minimal effect on the cross polarization performance of the proposed slot antenna. KEYWORDS slot antenna, coplanar waveguide, zero-index metamaterial (ZIM), metamaterial superstrate, gain enhancement 1 | INTRODUCTION The advancement of wireless communication system demands the design of high gain antennas with maximum possible size reduction for developing compact systems. However, reduction in size unavoidably leads to poor gain of the antenna. Thus, for effective communication, it is extremely important to enhance the gain of the antenna. There are several procedures that have been reported by many authors in context to the gain enhancement of planar antennas. The previous trend to enhance the gain of the pla- nar antennas were the use of a nonmagnetic or a plain dielec- tric, 1 a frequency-selective surface (FSS), 2 or an electromagnetic band-gap (EBG) structures 3 as a superstrate. The FSS and EBG types are exhibiting similar transmission and reflection characteristics which form a Fabry-Perot reso- nant cavity, and hence, the gain of the antenna has been enhanced. In Ref. 4, front to back ratio and gain enhance- ment of planar printed antennas has been elaborated using multilayer ADL structures. However, all these techniques require thick layers, leading to a significant increase of antenna profile. The development of metamaterials opened a new possi- bility for designers to create a novel structure with unusual properties like negative electric permittivity, negative mag- netic permeability and negative refractive index. In Ref. 5, it has been described that materials with near-zero refractive index can convert the diverging wave into plane wave. This property of MTM provides a unique way for enhancing the directivity and/or gain of an antenna. The characteristic of the propagation and scattering of electromagnetic wave in ZIM has been investigated in Ref. 6. The analytical formula- tion for the gain enhancement of patch antenna using MTM superstrate has been described in Ref. 7. Int J RF Microw Comput Aided Eng 2016; e21078 wileyonlinelibrary.com/journal/mmce V C 2016 Wiley Periodicals, Inc. | 1 of 10 Received: 19 July 2016 | Revised: 2 December 2016 | Accepted: 2 December 2016 DOI 10.1002/mmce.21078