Design of a wideband balanced waveguide HEB mixer employing a GaN buffer-layer for the 1-1.5 THz band

Paper in proceeding, 2017

We present the design and implementation of a wideband balanced waveguide NbN HEB mixer employing a GaN substrate in the frequency range of 1 - 1.5 THz. The balanced receiver scheme consisting of a 90˚ RF hybrid, a pair of NbN phonon-cooled HEB mixers and a 180˚ IF hybrid has major advantages over the single-ended configuration. The 3 dB RF hybrid is employed to couple the RF and LO signal into the HEBs, and allows for the efficient use of available LO power. Furthermore, the usually small IF bandwidth of phonon-cooled NbN HEB mixers has been addressed by employing a GaN substrate instead of a conventional substrate, e.g., Si or quartz. It has recently been shown that using GaN substrate reduces the escape time of phonons from NbN bridge to the substrate and thus, prospectively enhances the overall cooling rate of hot electrons and yielding higher IF bandwidth. The mixer housing is implemented in a back-end configuration and has been fabricated by means of a micro-machining method, providing excellent control of the dimensions and smoothness of the all-metal waveguide components. The expected RF performance of the proposed HEB design as well as its fabrication and DC characterization are presented