Impedance measurements at millimeter wave frequencies (54.2 GHz)

Abstract

A WAVEGUIDE CIRCUIT (Figure 1) has been designed and constructed to measure impedance a t millimeter wave frequencies. To calculate the load impedance, known standards were used to characterize the network transformation between the p l y e of measurement and the load location. Measurements were performed at 54.2 GHz on specially fabricated loads and on mm-wave PIN diodes. A series of independent measurements were made to determine the relative phase and magnitude of the complex reflection coefficient of the load. Bolometer measurements at the output of the 3-dB coupler are essential to the circuit design. The phase was measured by the amount of cancellation which occurs when the reflected signal is fed into the 3-dB four-port directional coupler and compared to a reference signal fed into the other input port. The magnitude was measured by comparing the signal reflected from the load to that reflected by the reference short (waveguide switch #l) . During the latter measurement, the reference signal is terminated (waveguide switch #2).