ially the same as that obtained for the wideband detector in (1) of Section 1.2.2.1. 1.2.2.2 The Problem of Frequency Synchronization (1) Doppler Effects For LPI scenarios in which the interceptor assumes the position of an enemy search aircraft, very significant Doppler shifts over the SS bandwidth can occur due to his velocity. The largest shifts occur for the lowest aircraft altitudes as the aircraft velocity component in the direction of the radiating source is nearly equal to the aircraft velocity. Since typically the interceptor is unable to know his velocity and altitude precisely, and certainly not his range, it should be easily appreciated that a PB-FBC having 125 channels randomly scattered across the frequency band will not have the channel cen- ter frequencies coincident with the received hop frequencies. In fact, if a hit occurs, the frequency error can, in many circumstances, be considered to be more or less any value across the filter passband with a uniform probabil- ity of occurrence. (2) Performance of the FBC with Frequency Error First it should be noted that the performance equation (1.9) for the FBC does not take intoa ccount the hop pulse energy lost due to the channel fil- ter. Thus, the effective signal power at the input to the square-law detector 8Note that, as in the case of the ideal filter bank combiner, the (S/No) result must be multiplied by h, which represents a correction factor from a Gaussian assumption to chi-squared statistics. Interception Detectors following the filter will be reduced by the factor (1.57) where H(f) is the equivalent lowpass transfer function of the bandpass filter. If, for simplicity, an ideal rectangular-shaped filter characteristic is assumed, viz., H(f)| (1.58) otherwise then (1.57) simplifies to = 0.7737 = -1.1 dB. (1.59) Because the channel or filter which coincides with a given hop pulse does not pass all of the pulse power, adjacent channels must contain propor- tional amounts of the "spillover." In particular, the i-th adjacent channel, i = +1,+2,+3