What question did this study set out to answer?

The research aims to design and characterize a superconducting 90° hybrid for wideband heterodyne receivers.

June 13, 2026Open Access

A 4–20 GHz Superconducting 90◦ Hybrid Using Capacitively Loaded Coupled Lines for 2SB Heterodyne Receivers

Key Points

The research aims to design and characterize a superconducting 90° hybrid for wideband heterodyne receivers.
Designed a broadband superconducting hybrid covering 4–20 GHz using capacitively loaded transmission lines.
Conducted cryogenic measurements with Vector Network Analyser for performance evaluation.
Assessed amplitude and phase imbalance metrics across the frequency band.
Achieved amplitude and phase imbalance of better than 0.6 dB and 6°, respectively.
Observed image-rejection performance in the 10–20 dB range in the full receiver setup.
Demonstrated potential for enhancing spectral grasp in millimeter and submillimeter observational studies.

Abstract

We report the design and cryogenic characterisation of a broadband superconducting 90◦ intermediate-frequency (IF) hybrid covering 4–20 GHz for sideband-separating (2SB) heterodyne receivers. The hybrid is implemented in thin-film niobium using capacitively loaded edge coupled transmission lines, avoiding the air-bridge interconnections required in Lange-coupler layouts while retaining a compact superconducting implementation with low loss and good quadrature balance. Cryogenic measurements using Vector Network Analyser (VNA) show amplitude and phase imbalance better than 0.6 dB and 6◦, respectively, across the full band. When used in a 2SB receiver, this level of IF balance is consistent with the observed image-rejection performance in the 10–20 dB range, for the full receiver. The design supports the development of wide-instantaneous-bandwidth 2SB receivers for millimeter and submillimeter observatories, improving spectral grasp for broadband line surveys and high-redshift line searches.

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