In many applications, such as radar warning receivers (RWRs), there is a need to detect short-pulse signals with high probability.
Frequency-swept detectors and spectrum monitors are not well-suited to being short-pulse signal detectors since they suffer low dwell times in each frequency band.
Short-pulse signals can be detected using a digital instantaneous frequency measurement (IFM) technique based on an analogue frequency discriminator and reference is made to P. L. Herselman and J. E. Cilliers: “A Digital Instantaneous Frequency Measurement Technique using High-Speed Analogue-to-Digital Converters and Field Programmable Gate Arrays” (2007). A conventional frequency discriminator typically comprises a splitter, a delay line, a mixer and a low-pass filter. Using the splitter, delay line and mixer, an input signal is mixed with a delayed copy. The product is fed through a low-pass filter. The frequency of a single input tone can be found using a look-up table. However, one drawback of such a system is that it can “blinded” by an extra input tone. Another drawback is that such a system tends to suffer from having a limited dynamic range.
US 2011/0053538 A1 describes a high-speed frequency sensor. The sensor comprises a plurality of filters allowing passage of signals over a different band of frequencies and a plurality of detectors, each associated with a respective filter. If the incident RF signal results in a signal in the band of frequencies passed by a particular filter, the detector associated with that filter generates an output signal. This indicates in which of the frequency bands the incident RF signal has been detected. The precision of the frequency estimate is limited to one bin per filter, that is, the sensor determines only a range of frequencies within which the single frequency exists, the range being equal to the band of frequencies passed by the filter.