Millimetre-Wave Direct Detection Receivers for Earth Observation Instruments – Trends and Challenges

Advances in semiconductor technologies and integration techniques have paved way for continuous performance improvements in passive mm-wave instruments and sensors. Extending the operating frequencies towards the THz region and improvements of noise Figure and 1/f noise performance have become possible through continuous developments in very short gate-length low-noise metamorphic GaAs and InP MMIC processes and in Schottky detector technologies. While these technologies are the keys for heterodyne radiometers, they are in fact enablers for direct detection (DD) receivers. Concept of direct detection is one of the current trends which is dependent on developments in mmwave and sub-mm wave LNA technologies, zero-bias Schottky detector devices and RF channel filters. These blocks shall offer adequate sensitivity, low power consumption and minimum volume tojustify the development and inclusion of the receivers in focal arrays and in small satellites. In this paper, we will refer to the latest achievements and justify the future development plans and specifications of direct detection radiometer developments for future ESA missions.