Q-band bandpass filter designs in heterodyne receiver for radio astronomy

This paper presents two Q-band bandpass filter designs that are targeted for application in the Atacama large millimeter-wave and submillimeter-wave array (ALMA) radio telescope. The bandpass filter is required to reject the lower side band from 15.2~29 GHz and retain minimum loss across the passband of 31.3~45 GHz. The bandpass filter based on WR22 waveguide is first presented. Specifically, the measured in-band insertion loss is around 0.4 dB, and the rejection of lower sideband is better than 34 dB. To further reduce the circuit size and to ease the integration with other MMICs in the receiver, a planar filter design based on GaAs process is also demonstrated. It will be applied to the multi-chip module version of the heterodyne receiver design to achieve more compact module size.