access icon free Varactor-tuned microstrip bandpass filters with different passband characteristics

© The Institution of Engineering and Technology
Received 29/08/2013, Accepted 20/11/2013, Revised 05/11/2013, Published 19/12/2013

Two novel types of tunable bandpass filters are introduced in this study. The first type is composed of varactor-loaded parallel-coupled lines and short-circuited stubs, which allows for the lower passband edge and two transmission zeros around the lower passband skirt to be reconfigured separately while the corresponding upper ones maintain fixed. The second type of tunable bandpass filter is built by cascading the first type of tunable bandpass and another tunable lowpass filter, which results in a great flexibility to tune both centre frequency and passband bandwidth. The designed prototype tunable filters are implemented using liquid crystal polymer (LCP) bonded multilayer printed circuit board (PCB) technology. The measured results demonstrate very promising performance in terms of wide tunability and high selectivity.

Inspec keywords: microstrip filters; circuit tuning; printed circuits; band-pass filters; low-pass filters; poles and zeros; coupled circuits; bonding processes; varactors

Other keywords: passband characteristics; LCP bonded multilayer PCB technology; short-circuited stub; transmission zero; tunable lowpass filter; varactor-loaded parallel-coupled line; varactor-tuned microstrip bandpass filter

Subjects: Printed circuits; Waveguide and microwave transmission line components; Capacitors; Junction and barrier diodes; Filters and other networks

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