Design of hexa-band microwave bandpass filter using modified T shaped multimode resonator

Abstract

Modern communication systems offer multiservice communication and they function in more than one frequency band. The transceivers of such multiservice communication systems require multiband microwave filters. Multiband filters are bandpass filters with more than one passband. Microstrips have been commonly preferred by engineers to fabricate microwave bandpass filters. The design of multiband filters using microstrips imposes several challenges. Dual band, tri band and quad band filters designed using microstrips can be found in the literature but their operating range span only up to 6 GHz. Also modern applications demand the number of passbands to be as high as seven. Accommodating several passbands within the microwave spectrum without affecting the insertion loss and return loss characteristics is a challenging task. In this paper a ‘T’ shaped microstrip resonator is designed and then modified to increase the number of passbands. The initial T shaped resonator possessed two passbands centered at 2.4 GHz and 5 GHz. The resonator dimensions and the substrate parameters are modified so that the derived filter possessed five passbands between 1 GHz to 14 GHz. A microstrip spurline is cascaded with the microstrip resonator to enhance the return loss characteristics at 13.3 GHz. A hexa-band microwave filter is thus achieved with satisfactory performance in terms of insertion loss and return loss at all six bands.