A 94 GHz radiometer for noise source calibration

Discusses how to design systems which are independent of the use of tuning elements. This implies that the effects of input mismatch must be accounted for in some other way. This paper describes how the problem has been solved in a 94 GHz radiometer at the National Physical Laboratory (NPL) Noise Standards laboratories based at RSRE Malvern. The author shows a block diagram of the radiometer system employed for calibration of noise sources in the frequency range 75 to 110 GHz. The radiometer is of the total power type. Two known and one unknown noise source are connected in turn to the input of the system using the waveguide switch. The output power as indicated on the power meter is kept constant each time by adjustment of the rotary vane attenuator. The value of the unknown noise temperature is calculated from a knowledge of the two known noise temperatures, ambient temperature and the three attenuator values