With the progress of radar technology, wideband instantaneous frequency measurement is a compulsory functionality of informationization equipment. In the paper the working principles and frequency measurement and application scenarios of an ultra-wideband electronic warfare receiver are studied in the terms of both theory and experiment. A simplification MonoDFT algorithm is proposed. It is realized to high-precision frequency measurement from 2GHz to 18GHz radar signal emitter. It is designed into two application scenarios and realizations. The analysis and experiment results show that the receiver can adapt to the instantaneous bandwidth 16GHz, a sensitivity more than -70dBm, frequency measurement accuracy over 0.4MHz, and a processing delay time of less than 270ns. The receiver is of high engineering application value in the electronic warfare field.