IFM Receiver Based on Microwave Frequency Discriminator That Uses Rat-Race Directional Couplers

Instantaneous frequency measurement (IFM) receivers are used, among other things, to perform fast measurements of very short microwave signals and in reconnaissance receivers of electronic warfare (EW) systems. The important components of an IFM device include a microwave frequency discriminator (MFD) and a microwave phase discriminator (MPhD). The MPhD principle of operation is based on vector summing of microwave signals. The coupled line or branch line directional couplers are often used to quickly handle these operations. As an alternative to these solutions, the authors propose the use of rat-race directional couplers in MFD design, presenting herein an as-built design of a developed device and measurement results.