Harmonic reduction using EBG structures

Abstract

Microstrip patch antennas are a class of planar antennas which have been researched and developed extensively in the past three decades. They are used in many applications in military and wireless communication systems. They have been an attractive choice in mobile and radio wireless communication. They have advantages of having a low profile, conformal, low cost, and robust and can be designed for dual polarization as well as multiple frequency applications. Out of the many feeding techniques for Microstrip antennas, proximity coupling is preferred because of advantage of high bandwidth, less spurious radiations, good suppression of higher order modes and better high frequency performance. In this technique, two dielectric substrates are used such that the feed line is between the two substrates and the radiating patch is on top of the upper substrate. The Microstrip antennas have disadvantages of low efficiency, narrow bandwidth and surface wave losses. In the 1990s, researchers suggested that electromagnetic bandgap structures or EBG be introduced into the printed antenna substrate, which have the capability of removing unwanted substrate modes. EBG structures operating in the high frequency and the microwave frequency bands are periodic or quasi-periodic patterns which are created by inclusions in dielectric or magnetic materials. When these inclusions are in ground plane and are also periodic in nature, the structure so obtained is known as an EBG structure whereas if these are non periodic in nature, the structure is a defected ground structure or DGS. The present work aims at the designing and implementaion of a simple proximity coupled Microstrip antenna and its integration with EBG and DGS structures. With the use of EBG structure, the harmonics are considerably reduced and the return loss of antenna at resonant frequency is increased without affecting the radiation characteristics. Two different structures are studied one is a perforated EBG structure and the other is a single patch mushroom EBG structure. Also, the behaviour of DGS when used with single patch mushroom EBG structure is analysed. This results into multiple resonant frequencies, giving a triple band. The bandwidth of antenna is enhanced using a slot in the feedline and the ground plane. A simple proximity coupled Microstrip antenna is designed to resonate at 1.52 GHz and the various parameters affecting the behaviour are studied such as patch width and feedline length. A perforated EBG structure with a bandgap between 5-6 and 9-11GHz is used to reduce the harmonic radiation from a PCMA resonating at 3.6GHz. The return loss at fundamental frequency improves by 15dB. A single patch mushroom EBG structure with a bandgap centred at 6.6GHz is used to reduce the third harmonic radiation from a PCMA resonating at 2.2GHz. The return loss at fundamental frequency improves by 15dB. The bandwidth of the conventional PCMA is enhanced by 73% with a slot in the feedline and the ground plane. Also, a DGS is used in PCMA with EBG which results in triple band and resonates at 1.43GHz, 2.61GHz and 3.17GHz.