Implementation of Dual Window Tapered Annular-Ring Electromagnetic Bandgap Filter Structures with Varying Aspect Ratio

Abstract

Filtering of undesired frequencies can be done by using shunt stubs and stepped impedance lines. These techniques are typically narrow band and require large circuit area. In order to solve the problem of conventional filters, one possible way to reject a band of frequencies is to use Electromagnetic Bandgap (EBG) Structure. Periodic structures that allow circulation of electromagnetic waves in a specific frequency band for certain angles of incidence and polarization senses are known as electromagnetic band-gap (EBG) structures. The peculiar feature of 2-D EBG structures is the presence of the stopband where electromagnetic waves are prohibited to propagate. It has been widely used as the dielectric material of high frequency circuits such as patch antennas to suppress the interfering waves between two closely placed antennas.2-D EBG structures shows good compatibility with microstrip circuits which make them work efficiently as bandstop filters. In EBG structures a stopband occurs when the periodic elements like circles are etched in the ground along with modulated microstrip line at an upper face of substrate. The behavior of EBG materials can be improved with the proper choice of tapering coefficient in correspondence with aspect ratio control factor. In this thesis, non uniform dual window tapered annular ring EBG structures are designed in order to observe any improvement over the conventional uniform circular-patterned EBGs. The main aim of this thesis is to design a compact EBG based microstrip structure with large bandwidth and stopband attenuation with small ripple level in both the lower and higher passband. In this thesis, the concept of PBG/EBG structure is presented along with the applications and advantages. With this EBG configuration; the proposed structure displays an ultrawide stopband with high attenuation within a small circuit area.The non uniform dual window tapered annular ring EBG structures with aspect ratio 0.4 and 0.25 for outer and inner circles respectively has been designed using the Computer Simulation Technology (CST)-2010 studio suite software and this simulated annular ring EBG Structure has been fabricated using Printed Circuit Board (PCB) technology and in order to have more precise practical results this fabricated design is tested on Agilent Vector Network Analyzer (VNA) of model no : N9917A ,with frequency range 4GHz-16GHz, comparison between the measured results and simulated results are also discussed. A brief summary of the contributions regarding the present work and suggestions for future research work conclude the thesis.