  This letter presents an experimental characterization technique for assessing
the performance of terahertz harmonic mixers across a wide frequency range. The
total signal transfer loss of three mixers was measured in both up- and
down-conversion configurations, and the conversion loss was determined through
the solution of a linear system of equations. The proposed method uses LO
signals with a frequency offset to ensure single sideband measurements, thereby
eliminating the need for image-reject filters. The three-mixer method was
verified by measurements of millimeter-wave mixers, which matched the
traditional characterization method using a calibrated source and power meter.
Given this successful millimeter-wave demonstration, we characterized three
WM-86 Schottky diode x4-harmonic mixers from 2.2 to 3 THz. This technique
presents a notable advantage for conducting broadband mixer characterizations,
particularly in the terahertz frequency regime which lacks tunable, wide-band
sources.
