Millimeter-Wave Quasi-Elliptic Filters in Groove Gap Waveguide Technology Using Overmoded Cavity with Spurious Coupling Suppression for Next-Generation SATCOM Applications

Abstract

This paper addresses the issue of sidelobe imbalance due to spurious coupling in quasi-elliptic filters designed in groove gap waveguide (GGW) technology using TE102�overmoded cavity based resonator to realize the cross coupling in the cascaded quadruplet topology. The filter is designed at 38 GHz with 750 MHz bandwidth (1.97% fractional bandwidth) to demonstrate its potential as a narrow-band, high-power output filter at mm-wave frequencies in next-generation high throughput satellites. The filter is designed for production yield avoiding any complex structures to realize the negative cross coupling and using an all-capacitive iris structure. Systematic studies have been performed to identify and mitigate the sidelobe imbalance issue, and a final design has been proposed with a very low (<1 dB) sidelobe imbalance. The measured results of the realized hardware closely match simulated ones. The proposed design configuration is an ideal filter option for next generation SATCOM applications as it provides benefits of narrowband symmetrical frequency response with low insertion loss, sharp near band rejection, and high-power handling capability along with the benefits of gap waveguide technology in terms of ease of fabrication, low passive intermodulation (PIM) level, and low sensitivity towards surface imperfections and misalignment issues.