Microwave Frequency Measurement Techniques can be done by the use of wavemeters.
A wavemeter is an adjustable resonant circuit provided with a calibration that gives the resonant frequency in terms of the settings of the tuning adjustment.
Wavemeters are used to measure frequency when the higher accuracy of a primary or secondary standard is not required, and where simplicity and portability are important.
A wavemeter may employ any type of resonant circuit that is convenient for the frequency range to be covered. Hence resonant circuit based on lumped constants, co-axial two wire lines and cavities, all are used in a wavemeter.
Wavemeters may employ absorption, reaction or transmission devices.
In the absorption type, the wavemeter is equipped with means for indicating the current induced in it. The wavemeter is then loosely coupled to the whose frequency is to be determined, and is adjusted for maximum response.
In the reaction type, the adjustment of the wavemeter corresponding to the frequency being measured is determined from the reaction produced by the wavemeter upon the system being measured. For example, the resonant frequency of a low power oscillator may be readily measured when loosely coupled to the tank circuit of the oscillator. The dc grid current will drop abruptly when the coupled wavemeter is tuned through resonance with the frequency being generated by the oscillator.
In the transmission type, the wavemeter is used as a coupling device in a system that transmits power from a generator to a load or indicator. Such a system is proportional to the energy transfer, such that appreciable transmission of the energy to the load occurs only when the wavemeter is tuned to the frequency of the energy involved. Transmission wavemeters find considerable use at microwave frequencies.