Design of Improved Micro strip Filter Structures for Wireless Applications

Abstract

Microstrip filters are the essential components for the microwave and millimeter wave applications like these are used in satellite, radar and mobile applications. The conventional filters are being replaced now days by a low loss and the miniaturized filters. Also, there is an increasing interest towards the EBG (Electromagnetic bandgap) structures. As they are capable to reject undesired frequencies therefore certain bandgaps are observed which can be used to make filters. This thesis deals with the filters employing Electromagnetic bandgap structures. The first part deals with the technique to produce large attenuation in the stopband. A DMS (Defected Microstrip Structure) has been employed which causes large attenuation in the stopband. The structure with no DMS causes -20 dB attenuation and the structure with two DMS causes -25 dB attenuation whereas the structure with four DMS causes -30bdB attenuation in the stop-band. The second part deals with the tapering technique which minimizes ripples in the passband. In comparison to the Dolph - Tschebysheff array design, the Dolph - Tschebyscheff array design causes minor lobes with equal level but the Taylor produces inner minor lobe with constant amplitude and remaining minor lobes decrease continuously. The taylor tapering causes smoothening of the passband and produces large side lobe level on comparison with the uniform structure. The third part deals with a bandpass filter for S-Band applications which cover the frequency range from 2-4 GHz.