Tunable lumped-element bandpass filters for Cognitive Radio application

Abstract

In this thesis the design of bandpass filters tunable at 400 MHz – 800 MHz was under research. Microwave filters are vital components which provide frequency selectivity in wide variety of electronic systems operating at high frequencies. Due to the occurrence of multi-frequency bands communication and diverse applications of wireless devices, requirement of tunable filters exists. The one of potential implementation of frequency-agile filters is frontends and spectrum sensors in Cognitive Radio (CR). The principle of CR is to detect and operate at a particular available spectrum without interfering with the primary user’s signals. This new method allows improving the efficiency of utilizing allocated spectrum such as TV band (400 MHz – 800 MHz). The focus of this work is development of sufficiently compact, low cost tunable filters with quite narrow bandwidth using currently available lumped-element components and PCB board technology. Filter design, different topologies and methods of tuning of bandpass filters are considered in this work. As a result, three types of topologies of bandpass filter were simulated and realised. They use digitally tunable capacitors (DTCs) for adjusting central frequency at TV "white space" spectrum. Measurements revealed that schematics presented in this work have proper output response and filters are successfully tuned by DTCs.