Characterization of 94 GHz and 183 GHz planar schottky diode based radiometer modules

Millimeter wave radiometry is fast becoming a more widespread technique in imaging and non-destructive testing due to its inherent benefits over the visible spectrum. Transparency to most non-conductive materials combined with better spatial resolution of objects are a few underlining features of using millimeter waves. This paper describes the characterization of two broadband, planar Schottky diode based radiometer modules centered at 94 GHz and 183 GHz. The 94 GHz radiometer is built using a W-band fundamental mixer configuration while the 183 GHz radiometer uses a sub-harmonic mixer. The local oscillator scheme consisting of a 30 GHz source which is frequency tripled to 90 GHz is common to both radiometers. The frequency tripler has measured conversion efficiency of 10%. The IF bandwidth for the fundamental mixer is about 18 GHz while the sub-harmonic mixer is 10 GHz. The double-sideband mixer noise temperature for both front end mixers was measured to be around 600 K with a conversion loss of approximately 5-6 dB. Radiometer characterization for noise equivalent temperature difference will also be presented.