S-Band Voltage Tunable Microstrip Combline Filter Design

Abstract

In this paper, a third order voltage tunable combline microstrip bandpass filter is synthesized and manufactured. Varactor diodes are used as tuning elements. Filter is tunable around 2500 MHz covering approximately the band from 2.2 to 2.9 GHz. Simple design procedure, low insertion loss and small filter size are the main advantages of the proposed filter. Insertion loss changes between −2.79 to −2.26 dB and filter size is $2\mathrm{x}2$ cm2.