A square-law microwave transistor detector for wideband radiometers

This paper describes the design and measurement of a square-law microwave transistor detectors for wideband radiometers. To increase detector dynamic range a negative feedback was used in it. Theoretical analysis and CAD harmonic balance simulation were performed to optimize the detector circuit and find the optimal value of the feedback factor. Two variants of the detector were developed: on BJT and on FET transistors. Experimental hybrid circuits have been realized with discrete transistors, lumped elements and microstrip transmission lines. Results of measurement of detector main characteristics are given: transfer function, tangential sensitivity, dynamic range, frequency response, input VSWR. Dynamic range up to 55 dB was achieved (at 1 dB compression point and 1 kHz video-bandwidth) with flat frequency response up to 4 GHz. These square-law detectors may be used for precision measurements of microwave power, for example in modulation-type wideband microwave radiometers.