Overview

A hypothetical interception situation can serve to illustrate a probability of intercept calculation without using the window function approach. Assume that there is a radar whose radio frequency (RF) is changed randomly to one of N frequencies on a pulse-to-pulse basis, and that we wish to intercept this signal and learn as much as possible using a relatively slowly sweeping narrowband receiver. The receiver sweeps a band, B, corresponding to the band over which the radar s frequency hops. The receiver instantaneous bandwidth ? is equal to the spacing of the N radar frequencies (i.e., N ~ B/ ?). Suppose further that the receiver s sweep time is such that it stays open to receive a specified frequency for a time during which R pulses are transmitted by the radar.

The frequency scanning receiver can receive signals at essentially one frequency at a given time. If such a receiver is operating in the frequency range of a random frequency hopping radar, certain information concerning this radar will be available to the receiver. The calculations below predict the type and amounts of data that would be expected.

The only pulses of interest to the scanning receiver are those occurring at the frequency to which the receiver is tuned. Suppose the radar transmits on N discrete frequencies (or the receiver resolves N frequencies). Assuming the receiver is tuned to one of the N frequencies, then the probability that a particular pulse occurs...