A high-performance ultra-narrow bandpass HTS filter and its application in a wind-profilerradar system

Abstract

This paper reports a recent development of a narrowband high-temperaturesuperconducting (HTS) bandpass filter with a fractional bandwidth of 0.35%in the L band. The filter exhibits a 10-pole quasi-elliptic function responseimplemented with a cascaded quadruplet coupling structure. The measuredfilter shows a midband insertion loss of 0.26 dB and a return loss better than−15 dB overthe passband. Steep rejection slopes are obtained at the band edges and the measured skirt slope hasexceeded 120 dB MHz−1, resulting in an excellent out-of-band rejection very close to the band-edge. Combining thisfilter together with a special designed low-noise amplifier (LNA) as well as a cryo-cooler, anHTS subsystem was then constructed and mounted in the front end of a wind-profiler radarsystem, substituting the corresponding conventional parts. A field trial has shown that theHTS filter could markedly improve the sensitivity as well as the anti-interference capabilityof a wind-profiler radar system.