W-band six-port network analyzer for two-port characterization of millimeter wave transistors

A W-band (75–100 GHz) six-port network analyzer was constructed from discrete WR-10 waveguide components for the two-port S-parameter characterization of state-of-the-art submicron gate length high electron mobility transistors. The six-port was capable of measuring the phase of a circuit’s reflection or transmission coefficient to within a 6° and the magnitude to within 1.5% for large reflections and to within 10% for small reflections (return loss of 20 dB). A comparison between the six-port and a down-converter-type frequency extender for a conventional network analyzer revealed the superior performance of the six-port. To demonstrate the applicability of the six-port network analyzer to device characterization, the S-parameters of 0.1-μm gate length HEMTs were measured and then used to calculate the maximum available gain achievable with these transistors at W-band frequencies. These measurements indicate the important role the six-port network analyzer will play in the future development of millimeter wave transistors.