Design of single-and dual-band bandpass filters using compact open loop resonator

Abstract

To design a bandpass filter with good performance, an open loop resonator within an inverted Y-type microstrip line is discussed in detail in this paper. Using a microstrip structure, the resonator is introduced in the filter design, and single- and dual-band bandpass filters, with dual-mode and more compact size, have been investigated. The single band bandpass filter is much smaller in size than conventional filter with a single-mode open loop resonator operated around the same frequencies and two transmission zeros existing in the stopband. The position of transmission zeros can be easily adjusted by using a source-load structure. Moreover, based on the research above, two symmetric resonators are combined, and a dual-band bandpass filter is designed with sharp rejection and wide stopband due to four transmission zeros. The fabricated samples are tested to verify the design. Very good results have been obtained.