Asymmetric bandpass filter using a ceramic structure

Abstract
A ceramic bandpass filter with increased selectivity on the lower side of the passband is presented. One application is the receive filter of a mobile radio transceiver operating in the 1.8-GHz bands. Finite transmission zeros have been introduced by using a network with additional cross couplings. The circuit was constructed with four coaxial ceramic resonators capacitively coupled using a microstrip PCB. For a 75-MHz passband filter, a stopband attenuation of 37 dB was attained at 20-MHz offset from the passband. A midband insertion loss of 1.2 dB and bandedge loss of 3 dB were achieved.

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