This paper describes the design and performance of the single-pixel receiver elements in the Cryogenic Array Receiver for Users of the Sardinia Observatory (CARUSO). CARUSO contains an array of 4x4 extended-W-band pixels, covering astronomical source frequencies from 70 to 116 GHz. CARUSO has recently been installed at the Gregorian focus of the 64 m diameter Sardinia Radio Telescope. Each cryogenic receiver pixel comprises a smooth walled feedhorn and a waveguide orthomode transducer for polarization separation. Each polarization channel comprises two low-noise amplification modules with a waveguide isolator between them, and an image-rejecting sub-harmonic mixer delivering the upper and lower sidebands, with a frequency tripler providing the local oscillator signal. The low noise amplifiers are based on two-stage MMIC amplifiers, incorporating InP high electron mobility transistors.

A room temperature sub-millimetre-wave Schottky barrier diode heterodyne receiver system (the Collaborative Heterodyne Astronomical Receiver for Mexico aka CHARM) operating at ~360GHz, has been deployed at the Large Millimetre Telescope, Mexico. The receiver is fully integrated as a turn-key system, and uses a double-sideband subharmonic mixer with an average noise equivalent system temperature of 1,000K. The system back-end signal processing incorporates four wide-band digital spectrometers, with a combined instantaneous IF bandwidth of 10.4GHz for both upper and lower side-bands, and a channel spectral resolution of 1.2MHz. The system has been used to observe first light with the LMT in the sub-millimetre-wave range. It will be further used to perform estimates of the telescope system performance in support of future sub-millimetre-wave observations from the LMT.

RAL Space has delivered four engineering qualification model (EQM) front-end receivers (FERXs) for the Microwave Sounder (MWS) and Microwave Imager (MWI) on-board the MetOp Second Generation (MetOp-SG) satellites. This mission will provide the European and wider global communities with weather forecasting services from 2022 to 2043. The two EQM FERXs developed by RAL for the MWS operate in the 183 and 229 GHz frequency ranges, featuring average double sideband (DSB) noise figures (NFs) of 5.3 and 6.2 dB, respectively. This paper presents the design and main characterisation results of these two state-of-the-art FERXs for the MWS and compares their performance with other in-orbit microwave sounding instruments, including those on-board MetOp.

An airborne heterodyne radiometer has been developed at the Rutherford Appleton Laboratory in order to observe oxygen spectral signatures around 60 GHz at an altitude above 40 km with high spectral resolution. It comprises low noise millimeter-wave amplifiers and a diplexer to split the channel into the lower side band (50.3 GHz - 57.3 GHz) and the upper side band (63.3 GHz - 67.9 GHz). A Schottky mixer in each band dowconverts the incoming signal into the intermediate frequencies (IF) and is then processed using a novel wideband fast Fourier transform digital spectrometer, which has an instantaneous bandwidth of 8 GHz and spectral resolution of 3 MHz. For this radiometer, we have measured a double sideband system noise temperature of less than 200 K and a noise equivalent differential temperature of 0.3 K for a spectral bandwidth of 10 MHz and an integration time of 300 milliseconds. The sideband rejection measured between the upper and lower sidebands is better than -45 dB.

Rutherford Appleton Laboratory Space Department (RAL Space) and Radiometer Physics GmbH are responsible for the provision of millimetre-wave front-end receivers operating from 165 GHz to 664 GHz for three instruments on board the MetOp Second Generation (MetOp-SG) satellites. Qualification of the Engineering Qualification Models (EQMs) is recently completed. This paper presents the results of the EQM qualification for receivers operating at 165 GHz, 183 GHz and 229 GHz for the MWS and MWI instruments.

RAL Space and its project partner PRG are tasked with providing space-qualified heterodyne receiver front-ends operating between 165.5 GHz and 325 GHz for the Microwave Sounder (MWS), the Microwave Imager (MWI) and the Ice Cloud Imager (ICI) of the MetOp Second Generation (MetOp-SG) series of satellites. The preliminary design of the receiver front-ends is now complete. Extensive tests on performance of the individual components, as well as of the assembled breadboard versions of the receiver front-ends, have been performed. The results and conclusions derived from these tests will be presented.