Design and performance of 90 GHz radiometer front ends

Results of prototype radiometer frontends at 90 GHz are described, using encapsulated whisker diodes. The diodes were embedded in a commonly used reduced height waveguide, but in addition, a special fixture was allowed to move the diodes up and down in respect to the waveguide or to turn it. This led to a very simple matching procedure. The mixers were easy to balance. LO-power was achieved using a 45 GHz-Gunn-oscillator followed by a varactor-doubler. The unit has a effeciency of 14 percent delivering an output power of about 10 mW at 90 GHz. Including isolator losses (0.6 dB) and IF-noise figure (2.5 dB), the dsb noise figure of the entire front end was about 9 dB, whereas the single mixers dsb noise figure was less than 4 dB.