Abstract

Microwave printed filters are preferred in modern mobile and satellite communication systems due to low cost, compact size, and high accuracy. In order to facilitate circuit integration and achieve high information capacity in a communication system, volume miniaturization and bandwidth modulation of the filters becomes critical. Such requirements make design and implementation of filters extremely challenging. Hence, the work presented in this thesis is focused on two aspects, namely, compact printed filter design and effective bandwidth modulation techniques. First, a simple composite right/left handed (CRLH) transmission line (TL) structure is proposed. Based on this structure, a bandpass filter which offers several advantages ( e.g. compact size and low loss over traditional filters) is designed. A CAD algorithm for automated CRLH filter design is also implemented, and demonstrated through a practical example. Second, a set of ring filters with adjustable bandwidths are proposed. These filters are implemented by a combination of hairpin resonators, interdigital capacitors and/or etched slots, leading to considerably wider bandwidths as compared to traditional ring filters. In addition, by changing the geometrical parameters of the interdigital capacitors and etched slots, the bandwidth can be easily adjusted for different applications. The filters feature two transmission zeros, whose locations can be accurately determined by means of the semi-analytical model developed as part of this thesis. The proposed filter units can be cascaded to obtain sharper cutoff frequency responses. Several these filters have been fabricated and tested using Anritsu 37369D vector network analyzer. The frequency responses from measurements are in good agreement with those from simulations in the 5-9 GHz range.