Copyright © 2018 Authors. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. International Journal of Engineering & Technology, 7 (3.6) (2018) 13-20 International Journal of Engineering & Technology Website: www.sciencepubco.com/index.php/IJET Research paper Optimization of Electromangnetic Band Gap Structure for Mutual Coupling Reduction in Antenna Arrays-A Comparative Study K. Praveen Kumar 1 *, Habibullah Khan 2 1 Lecturer, Dept. of Electrical and Electronics Engineering, Eritrea Institute of Tech., Mainafhi, State of Eritrea, East Africa. 2 Professor, Dept. of ECE, KL Deemed to be University, Vaddeswaram, A.P, India. *Corresponding author E-mail:kpraveenkumar24817@gmail.com Abstract In this paper, two new three layer (stacked) Electromagnetic Band Gap structures are proposed, named as Stacked Electromagnetic Band Gap (SEBG) and Progressive Stack Electromagnetic Band Gap (PSEBG) structures. Its electromagnetic (EM) properties are determined by using Finite element method (FEM) based simulator and obtained results are compared with classical mushroom type electromagnetic band gap (MEBG) structure. Both SEBG and PSEBG structures proposed in this paper consists of two layers above the conducting ground plane; a lower layer, contains array of small MEBGs with square patches and an upper layer contains square planar MEBG structure. Vertical conducting stubs passing through substrate shorting all square patches in both the layers with conducting ground. Three EBG structures are exhibiting the property of forbidden band gap (FBG), where surface wave propagation is restricted. The FBG property helps in minimization of mutual coupling between array antennas when electromagnetic band gap structures are incorporated between array elements. In this paper, the level of coefficient of mutual coupling between array antenna in the presence of SEBG and PSEBG are investigated, obtained results are compared with classical MEBG results. The co-efficient of mutual coupling is reduced up to 12dB in the presence of proposed models. 1. Introduction The microstrip patch antennas are arranged in an array, for high gain, beam steering [1] applications. Array architecture of consists of multiple number of antenna elements printed on common substrate. This may cause mutual coupling between antenna elements because of excitation of surface waves, space waves and overlapping of near fields between the array elements. This results in reduction of antenna performance in terms of antenna gain, operational bandwidth and radiation efficiency as well as overall system performance [2]. Practically, the coupling mechanisms depend on several factors such as permittivity and thickness of substrate material, ground plane size, type of excited modes etc. [3]. In generally, physical distance between the antenna elements is maintained half an operating wave length to reduce mutual coupling [4]. Various techniques have been proposed in literature to reduce the mutual coupling between array elements such as: corrugations [5,6], split ring resonators (SRR) [7,8] and Defected Ground Structures (DGS)[9-11]. In [12] MEBG is proposed and applied to improve the isolation of radiating elements in an array by suppressing the surface wave propagation. Various EBG architectures were designed [13-19] and applied to antenna arrays for mutual coupling reduction. In this paper, MEBG surface have been chosen as a base of designing new SEBG and PSEBG surfaces. Both the structures consists of three layers; top layer contains square planar MEBG unit cell, lower layer (middle or hidden layer) contains small square array of MEBG unit cells and bottom layer contains a plane conducting sheet, all the patches are shorted to plane conducting sheet at bottom layer by vertical conducting stubs centrally to the patches through FR4 substrate. The overall size and individual particles of proposed SEBG and PSEBG unit cells are small compared to its operating wavelength. The shape and dimension of individual elements of unit cell plays key role for synthesis of its frequency response, FBG and AMC properties. The FBG property of EBG unit cell permits no surface propagation. The surface wave propagation between antenna elements is root cause for mutual coupling so by introduction of EBGs between array elements one can reduce the co-efficient of mutual coupling or improvise the isolation. The objective of this paper is to introduce two new electromagnetic band gap structures named as SEBG, PSEBG and determine its efficiency in reducing coefficient of mutual coupling in antenna arrays. The first part of the paper contains design procedure of SEBG and PSEBG structures and their emerging from fundamental MEBG is explored and its FBG property is determined using FEM based simulator. In second part, the level of coefficient of mutual coupling between E-plane array antenna by the introduction of new SEBG and PSEBG is studied and obtained results are compared with the results of MEBG model. 2. Unit Cell Design Figure 1 to 3 showing the schematic diagrams of MEBG, SEBG and PSEBG. The MEBG is considered here as reference structure. All EBG models are designed on FR4 substrate, relative permittivity of 4.4, permeability of 1 and loss tangent of 0.02 with a thickness (height) 'H' of 3.2mm (124mil). The lattice in Figure 1 consists of square metal patch of 17.5X17.5 mm 2 printed on one