The circuit configuration, operational principles, and some test data on three new types of equalizers applicable for use in FM microwave radio links are described. The equalizers are namely of the reflection type, frequency converter type, and AM-PM conversion type. The reflection type delay equalizer permits variation of relative delay time while keeping the absolute delay time constant at the center frequency or permits variation of absolute delay time while keeping the relative delay time constant. The frequency converter type equalizer adopts a principle whereby variation in local frequency (supplied to the frequency converter) facilitates continuous variation of the relative delay time, absolute delay time, and amplitude frequency response. The AM-PM conversion type differential gain equalizer enables equalization of differential gain through the combined use of the AM-PM converter circuit and the delay circuit.