Fifty years of instantaneous frequency measurement

Quadrature phase discriminators, the core of wideband instantaneous frequency measurement (IFM) receivers and multiple base-line interferometry for accurate direction finding (DF), were invented in 1957, by S.J. Robinson of Mullard Research Laboratories (MRL). Digital instantaneous frequency measurement (DIFM) receivers have been universally used operationally for wideband monitoring of radar environments in naval, airborne and ground-based electronic support measures (ESM) systems all over the world for over 50 years. Their importance is such that many countries have developed their own IFM manufacturing capability with just minor architectural changes to the original design. This study describes the invention sequence, the development history, IFM design and performance principles, its general use and limitations in modern electronic warfare (EW) systems and ends with a projection for the future.