Multilayer Quasi-elliptic filters using dual mode resonators on Liquid Crystal Polymer Technology

Microstrip pseudo-elliptic bandpass filters using dual mode resonators, operating in the X-band, have been designed and implemented on multilayer liquid crystal polymer (LCP) technology. LCP is emerging as an attractive technology for RF/ microwave solutions due to its superior electrical characteristics and its ability to act both as a substrate and package. Slotted patch resonators printed on different dielectric surfaces and sharing the same ground plane are coupled through slots etched in the ground plane. Two different resonator arrangements to realize finite frequency transmission zeros are presented. Multilayer configuration is realized through thermocompression bonding of thin sheets of LCP, giving a 50% size reduction over a 2-D implementation. Fabricated fourth order filter prototypes exhibit good agreement with simulated results with a return loss level better than 10 dB, a 3 dB bandwidth of around 5.5% and an insertion loss of 5 dB. They also exhibit steep rejection in the vicinity of the passband edges with the help of a pair of finite frequency transmission zeros.