A Compact Sideband Separating Downconverter With Excellent Return Loss and Good Conversion Gain for the W Band

We have developed a sideband separating receiver module for the W band (75-110 GHz) that has been designed with a scalable and compact architecture allowing easy integration into larger systems, like focal plane arrays. The receiver includes a high-frequency amplification stage giving it a good conversion gain and, most importantly, due to its original architecture, excellent return losses. The latter permits, if needed, efficient incorporation of further amplification prior to mixing. The module is based on a 90° hybrid followed by an amplification stage and broadband mixers. As amplification stage, we rely on commercial low-noise amplifier chips that use the 70-nm metamorphic-highelectron-mobility process from OMMIC. The downconverter is a subharmonic mixer designed as a monolithic microwave integrated circuit and fabricated using the standard gallium-arsenide Schottky diode process from United Monolithic Semiconductor. The size of the module is 50 mm × 25 mm × 20 mm and shows good performance with an input return loss above 12 dB in the entire band, an average conversion gain of 5 dB, and sideband rejection ratio above 10dB in the majority of the band. The primary motivation of this article has been radio astronomy, but other areas like imaging, telecommunications, or remote sensing can benefit from such compactness and integrability into multibeam systems.