Review of microwave frequency measurement circuits

In this work, microwave frequency measurement (MFM) is reviewed since the early stages using fully analog implementations, including its evolution to analog/digital implementations with high resolutions up to 1 MHz. The review includes fully digital implementations and microwave photonics techniques, with a discussion on achieved devices and the overall field of measuring and identifying unknown signals. Several microwave planar devices such as interferometers, filters, and frequency selective surfaces have been proposed to design low-cost and low-power digital MFM systems. The planar devices presented here show resolutions from 1 MHz to 940 MHz and operate in the frequency range from 0.15 GHz to 11.5 GHz, having typical bandwidths from 1 GHz to 2 GHz. MFM using microwave photonics techniques involve mapping the microwave signal into the optical spectrum to create a frequency-power function, that uniquely identifies the frequency of the unknown signal, with large bandwidths and immunity to electromagnetic interference.