Calibrating network analyzers with imperfect test ports

The test ports on automatic network analyzers are generally built with an impedance that matches the impedance of the calibration standards. Experimental evidence is presented that substantial impedance discontinuities can be tolerated at the test port interface if proper calibration procedures are observed. The 50-Ω test port on one of the six-ports in a dual six-port network analyzer was replaced with a 75-Ω test port. This test port was then calibrated to look like a 50-Ω test port. Measurements on various devices show that it is possible to make a 75-Ω test port indistinguishable from a 50-Ω test port