Triple-mode dual-band bandpass filter on microstrip-to-CPW structure

A high-selectivity dual-band bandpass filter using a modified triple-mode resonator with two paralleled stubs is proposed. By adding a coplanar waveguide (CPW) structure into a microstrip dual-mode stepped-impedance resonator (SIR), the triple-mode resonator is achieved without significantly increasing the overall circuit size. Five transmission zeros are generated in the desired band so as to improve the filtering selectivity. Simulated and measured results show that the designed filter achieves good performance in terms of compact size and high selectivity.