A Cryogenic 180° Planar Hybrid for High-Sensitivity Radio Astronomy Receivers

A 180° hybrid is a fundamental component in microwave circuits, functioning as both a signal splitter and combiner in radio astronomy and space system applications. An ideal 180° hybrid provides equal power division with a 180° phase shift between the output ports in splitter mode, and coherent signal summation for inputs with a 180° phase difference in combiner mode. These hybrids are commonly employed as combiners in broadband Orthomode Transducers (OMTs). Therefore, the amplitude and phase imbalances of the hybrid directly impact OMT performance, dictating the 180° hybrid design specifications. This paper presents the design, fabrication, and experimental characterization of a planar 180° hybrid specifically developed for integration with an Orthomode Junction (OMJ) to form an OMT operating in the L-band (1.3–1.8 GHz) within a cryogenically cooled (20 K) radio astronomy receiver. The proposed hybrid minimizes physical footprint while ensuring high mechanical stability and reduced microphonic sensitivity — critical factors for preserving receiver sensitivity. The final device dimensions, optimized for integration within a cryostat, are 78 × 57.5 × 13 mm³, ensuring compatibility with space-constrained environments. This work demonstrates the successful realization of a high-performance planar hybrid suitable for cryogenic microwave applications, representing a significant advancement in the design of compact, low-loss components for precision instrumentation.