Electromagnetic band gap (EBG) technology has become a significant breakthrough in the radio frequency (RF) and microwave applications due to their unique band gap characteristics at certain frequency ranges. Since 1999, the EBG structures have been investigated for improving performances of numerous RF and microwave devices utilizing the surface wave suppression and the artificial magnetic conductor (AMC) properties of these special type metamaterial. Issues such as compactness, wide bandwidth with low attenuation level, tunability, and suitability with planar circuitry all play an important role in the design of EBG structures. Remarkable efforts have been undertaken for the development of EBG structures to be compatible with a wide range of wireless communication systems. This paper provides a comprehensive review on various EBG structures such as three-, two-, and onedimensional (3D, 2D, and 1D) EBG, mushroom and uniplanar EBG, and their successive advancement. Considering the related fabrication complexities, implementation of vialess EBG is an attractive topic for microwave engineers. For microstrip antennas, EBG structures are used in diversified ways, which of course found to be effective except in some cases. The EBG structures are also successfully utilized in antenna arrays for reducing the mutual coupling between elements of the array. Current challenges and limitations of the typical microstrip antennas and different EBG structures are discussed in details with some possible suggestions. Hopefully, this survey will guide to increasing efforts towards the development of more compact, wideband, and high-efficient uniplanar EBG structures for performance enhancement of antenna and other microwave devices.

Abstract-The periodic structure like electromagnetic band gap (EBG) is a hot research topic in the academia and RF-microwave industry due to their extraordinary surface wave suppression property. This study involved in designing a compact uni-planar type EBG structure for a 2.4 GHz resonant frequency band. Double folded bend metallic connecting lines are successfully utilized to realize a low frequency structure while a size reduction of 61% is achieved compared to the theoretically calculated size. From the transmission response, the surface wave band gap (SWBG) is found to be 1.2 GHz (1.91-3.11 GHz) whereas the artificial magnetic conductor (AMC) characteristic is observed at 3.3 GHz. The FEM based EM simulator HFSS is used to characterize the EBG structure. The SWBG property is utilized for alleviation of mutual coupling between elements of a microstrip antenna array. A 2 × 5 EBG lattice is inserted between the E-plane coupled array which reduced the coupling level by 17 dB without any adverse effect on the radiation performances.

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A planar pattern reconfigurable antenna designed for IEEE 802.11 b/g standard 2.4 GHz WiMax and WLAN applications is presented. The design is realised using a uniform arrangement of eight switch‐controlled tapered strips symmetrically placed around a central circular disc on the top layer of an FR4 board. The antenna has a compact circular structure with overall diameter of 0.64λ0 in the free space for 2.4 GHz. To control the radiation pattern of the antenna, each of the tapered strips is connected to the ground via a PIN diode. Depending on the switching status of the eight PIN diodes, the tapered strips work in grounded or open‐ended mode and thus the antenna offers eight switchable patterns. To validate the design, the antenna is prototyped and its performance is verified in a far‐field anechoic chamber. The simulated and measured results prove the antenna's reconfigurability of the main beam in eight directions with 45° steps in the azimuth plane and a vertical tilting angle of 36°. Over the operating band 2.35–2.61 GHz, the antenna has a stable gain of around 4.5 dBi, and front‐to‐back ratio of more than 18 dB. Compared with recent designs, this antenna is more compact, has larger beam deflection off the boresight and more beam steering states.