Abstract In Electronic Support, periodic search strategies for swept-frequency superheterodyne receivers (SHRs) can cause synchronisation with the radar it seeks to detect. Synchronisation occurs when the periods governing the search strategies of the SHR and radar are commensurate. As a result, the radar may never be detected. In this paper, we find that, under certain conditions, the number of ratios of periods that can cause synchronisation is finite. We develop theory that can enumerate all of the ratios and determine the intercept time. Index Terms Electronic support, superheterodyne receiver, emitter intercept, synchronisation, Farey series, radar warning receiver, scan-on-scan. I. Introduction The superheterodyne receiver (SHR) has long been a primary tool for Electronic Support (ES). The swept-frequency SHR has the advantage of being able to cover a wide bandwidth and, by virtue of its narrow instantaneous bandwidth, it is selective and sensitive. However, a key element to the effectiveness of the swept-frequency SHR in operational environments is its search strategy. The simplest strategy, and traditionally the most widely used, wholly or partly, is a simple periodic strategy, whereby the SHR repeatedly sweeps through the entire band of interest at a constant rate When a swept-frequency SHR is searching for a radar which is also employing a periodic search strategy, such as a circularly scanned or raster scanned radar, it is well known that synchronisation can be a problem [1]
