Tunable Band-stop Filter for Radiation Emission Test of Railway Locomotive Radio

Abstract

This paper designs a tunable narrow-band bandstop filter for radiation emission (RE) test of 450 MHz railway locomotive radio. The loading capacitance of the cavity is changed by the screw, and the center frequency of the band rejection filter is adjustable from 457.9 MHz to 467.9 MHz. Its narrow bandwidth is achieved by weak coupling between the main transmission and the cavity, and the stopband bandwidth can be adjusted by the coupling distance. When the center frequency changes, the stopband bandwidth remains the same with a 30 dB rejection bandwidth of 0.8 MHz. Using Step impedance resonator (SIR) structure, its volume is only half of the traditional cavity band stop filter, and its spurious stop-band is higher than 2 GHz, while the quality factor (Q-value) is very high, and its passband insertion loss is less than 1 dB.