Tunable Microstrip Bandpass Filter with Wide Tuning Range

Abstract

A tunable microstrip bandpass filter is presented. The filter is of a third order and based on general Chebyshev filtering response. It consists of three short-circuited microstrip line resonators whose length is λ/8 at the centre frequency of 1.5 GHz. The frequency tuning is achieved by connecting variable capacitors to the end of the resonators. The tuning range extends from 1.1 to 2.5 GHz. The insertion loss is better than -1 dB within the operating range. The proposed bandpass filter is designed and simulated using CST® software package. The simulated results demonstrate a good frequency selectivity, wide tuning range and low insertion losses.