A Novel Airborne Microwave Sounder Radiometer (Hyms)

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.