Time-Domain Reflectometer Measurement of Insertion Loss of High-Frequency Switches

High-frequency switches of the reed relay type have insertion losses of the order of 0.1 dB. The insertion loss is primarily the result of large skin effect impedance in the magnetically active portion of the signal path. This paper presents a novel time-domain reflectometer technique for measuring this skin effect impedance in the time domain then shows how a Fourier transform will convert the readings to either an impedance or insertion loss in the frequency domain. The method uses inexpensive equipment, is very accurate, and is fast since only a single voltage measurement at one instant of time is needed for the determination of the insertion loss at a desired frequency. Precision of at least 0.001 dB is achievable.