Microwave Attenuation Measurement by Time-Interval Ratio

A new method of measuring microwave attenuation using time or frequency as the reference is described. It is a power ratio type of system in which power flowing through the unknown attenuator is controlled by a constant pulsewidth, variable period, and pulse-modulated p-i-n diode switch. This power is detected by a thin-film thermocouple (TFT), the output of which is compared with that of a similar reference thermocouple whose input is a small constant fraction of the source power. The duty cycle required for equal thermocouple outputs is simply related to the unknown attenuation. The method is independent of detector linearity, and when compared with precise measurement standards, the system was found to be capable of measuring attenuation of up to at least 20 dB with an accuracy of ±0.001 dB/10 dB.