A bandpass filter with cross-coupled L-shape folded resonators for compact size and spurious suppression

This paper proposes a new microstrip resonator consisting of L-shape folded stepped-impedance line sections. The resonator has been applied for designing a four-pole cross-coupled bandpass filter. The full-wave simulator IE3D has been used to design and optimize the proposed L-shape folded stepped-impedance resonator and the four-pole cross-coupled bandpass filter. It has been found that the designed filter has a compact size and a low spurious response. Moreover, using the L-shape resonator, transmission zero levels of the frequency response can be adjusted. Experiments have been carried out and it has been found that the results are in good agreement with simulated expectations.