Filter-bank for broadband sub-mm wave superconducting on-chip spectrometers

DESHIMA 2.0 is a broadband sub-mm wave superconducting on-chip spectrometer for astronomy, targeting an instantaneous octave bandwidth (220 - 440 GHz) sampled with moderate spectral resolution channels (f/df ~ 500). In this work we propose a microstrip filter-bank implementation for DESHIMA 2.0 based on “H-shaped” resonators. These bandpass filters are free from spurious resonances over an octave bandwidth, do not suffer from radiation losses and can be arrayed in large filter-banks thanks to their extremely low reflections off-resonance. The design has been aided by an analytical circuit model that can fast and reliably predict the filter-bank behaviour. Prototype chips have been characterised in terms of frequency response and coupling efficiency.