With the growth of electromagnetic traffic, Electronic Warfare (EW) systems need to be more accurate or to use new characterizing parameters in order to discriminate radar pulses. Studying the signal frequency by estimating the Instantaneous Frequency Law (IFL) and Rate (IFR) offers some new opportunities that actual EW systems do not embed. From our knowledge, the use of multi-linear methods such as General Representation of Phase Derivatives (GRPD) in EW context has never been done. In this article, we describe the assumptions we must have for radar signals, especially the pulse width, to estimate the IFL and the IFR. Then, we show the potential contribution of multi-linear functions to EW by applying those functions to three different radar waveforms, particularly to waveform emitted by a Low Probability of Interception (LPI) Radar.