Classic EW relies on a threat library (or mission data file): a pre-programmed list of known threats with their characteristics and the matching countermeasure. An ESM system (EW: Electronic Support Measures) picks up a signal, looks it up in the library, and the jammer (Electronic Counter Measures) applies the right, pre-planned technique. That works fine — as long as you know the threat in advance.
Modern radars undermine that assumption. They are agile, multifunctional and software-defined: they change their waveform in milliseconds, combine functions and can transmit completely unknown signals. A fixed library is then by definition behind the times — and a threat that is not in it gets no countermeasure. This chapter covers two modern answers that you have not yet come across in the earlier chapters.