We present the design, fabrication and characterisation of a broadband leaky
lens antenna for broadband, spectroscopic imaging applications. The antenna is
designed for operation in the 300-900 GHz band. We integrate the antenna
directly into an Al-NbTiN hybrid MKID to measure the beam pattern and absolute
coupling efficiency at three frequency bands centred around 350, 650 and 850
GHz, covering the full antenna band. We find an aperture efficiency ηap≈0.4 over the whole frequency band, limited by lens reflections. We
find a good match with simulations for both the patterns and efficiency,
demonstrating a 1:3 bandwidth in the sub-mm wavelength range for future on-chip
spectrometers.Comment: Accepted for Publication at IEEE Transactions on Antennas and
Propagatio