High resolution IFMs

In this paper, three type of IFM (instantaneous frequency measurement) systems are presented. Classical IFM, consisting of directional couplers and power dividers, has been modified by applying phase shifters. Two other IFMs are also described. A diode ring was used in one IFM and only power dividers in another. Output signal conversion techniques are detailed. These IFMs, which can reach a frequency resolution better than 1 MHz, were examined practically.