This paper deals with evaluation and simulation of direct detection radiometer, which operates in the W-frequency band. Radiometers can be used in wide range applications in industry, military and security as well. One of the possible applications where the radiometers can be used is scanning of concealed dangerous objects. Main part of the article deals with the theoretical analysis of the basic total power radiometer parameters and their evaluation. Subsequently, the outcomes of the analysis are applied in design of radiometer model in Matlab® Simulink. In conclusion, the achieved results from experimental measurements are compared with calculated and simulated.