Anomalies observed in wafer level microwave testing

Two anomalies have been observed in the course of developing planar wafer level standards for the testing of GaAs monolithic microwave integrated circuits. The first involves a low-frequency characteristic impedance change of microstrip and coplanar waveguide transmission lines. This effect, which is due to conductor loss of the transmission media, can result in improper/inaccurate calibrations and measurements. The second anomaly results from resonant coupling of the microwave probe into adjacent structures on the wafer. This can occur during calibration or measurement and results in extreme inaccuracies at the resonant frequencies. Methods to eliminate these anomalies are addressed.