Millimeter wave radiometers for applications in imaging and nondestructive testing

This paper describes the development and characterisation of broadband radiometers centered at 94 and 183 GHz for passive millimeter wave imaging and NDT applications. The W-band radiometer has been built and tested using both fundamental and sub-harmonic mixer configurations. The 183 GHz radiometer uses a sub-harmonic mixer at the front-end and has an LO that is common with the fundamentally pumped W-band receiver. In this case the LO is supplied via a ~30 GHz source which is frequency tripled to 90 GHz with a conversion efficiency of around 10 %. The IF bandwidth for both fundamental and sub-harmonic W-band mixers is about 18 GHz while the 183 GHz mixer is 12 GHz. The room temperature DSB mixer noise temperature was measured to be around 500 K with a conversion loss of approximately 5 dB for 94 GHz and 183 GHz channels. NETD results for these radiometers are also presented.