Enhanced stop-band rejection by symmetric feeding in 1.8 GHz cross-coupled planar HTS microwave filters

Abstract

The superior performance manifested in characteristics of low pass-band insertion loss, high stop-band rejection, and sharp band edge skirt, has led the superconducting microwave filters one of the most attractive candidates for wireless communication applications. In this paper, we report the design and fabrication of the 4-poles cross-coupled planar microwave filters fabricated using YBCO superconducting thin films deposited on both sides of a LAO single crystal substrate by pulsed laser deposition. The resonator geometry allows one to miniaturize the 1.8 GHz filters onto a substrate with dimensions of 1 cm x 1 cm. We also demonstrate that by properly choosing the feeding configuration, filters with better selectivity, in particular with an additional pair of deep transmission zeros (poles) outside both sides of pass-band, can be achieved.