Quadruple-ridged flared horn feed with internal RFI band rejection filter

Abstract

This paper presents a new technique to reject the radio frequency interference (RFI) from the nearby radar at 9.4 GHz, which causes about 20% blockage of the sky coverage in the Very Long Baseline Inter ferometry (VLBI) telescope at the Goddard Geophysical Astronomical Observatory (GGAO), in Greenbelt, MD. An internal notch filter is proposed by inserting and optimizing two-quarter wavelength slots within the wide band Quad-Ridge Flared Horn (QRFH) feed to achieve RFI band rejection at 9.4 GHz. The simulated result shows about 95 % rejection at 9.4 GHz. The estimated attenuation due to the band rejection slots is of the order of .01 dB at frequencies distant from the rejection frequency. This technique will open the door for designing wideband feeds with RFI band rejection characteristics for different RFI sources