Editing Direction finding (section)

=== The new demands on DF systems ===
The move to microwave frequencies meant a reappraisal of the requirements of a DF system.<ref>Woolier D.F., "System considerations for naval ESM", IEE Proc. Vol. 132, Pt. F, No. 4, July 1985.</ref> Now, the receiver could no longer rely on a continuous signal stream on which to carry out measurements. Radars with their narrow beams would only illuminate the antennas of the DF system infrequently. Furthermore, some radars wishing to avoid detection (those of smugglers, hostile ships and missiles) would radiate their signals infrequently and often at low power.<ref>Wise J.C., "A Perspective on EW Receiver Design", Tech. Report APA-TR-2009-1102, J.C. Wise and Associates, Nov. 2009,  Find at:. https://ausairpower.net/APA-Maritime-ESM.html</ref> Such a system is referred to as a [[low-probability-of-intercept radar]].<ref>Davidson K., "Low Probability of Intercept", find at: http://radar-engineer.com/files/Lecture_LPI_Radar.pdf</ref><ref>Stove A.G. Hume A.L. and Baker C.j., "Low probability of intercept radar strategies", IEE Proc. Sonar Navig., Vol. 151, No. 5, October 2004</ref>  In other applications, such as microwave links, the transmitter's antenna may never point at the DF receiver at all, so reception is only possible by means of the signal leakage from antenna [[side lobe]]s.  In addition, covert [[Data link]]s<ref>Mills R.F. and Prescott G.E., "Detectability Models for Multiple Access Low-Probability-of-Intercept Networks", IEEE Trans on Aerospace and Electronic System, Vol.36, No.3, July 2000, pp> 848-858.</ref> may only radiate a high data rate sequence very occasionally.

In general, in order to cater for modern circumstances, a broadband microwave DF system is required to have high sensitivity and have 360° coverage in order to have the ability to detect single pulses  (often called [[amplitude monopulse]]) and achieve a high "Probability of Intercept" (PoI).<ref name = Hatcher>Hatcher B.R., [https://www.rfcafe.com/references/articles/wj-tech-notes/ew-acquisition-systems-probability-intercept-time-v3-3.pdf "EW Acquisition Systems - probability of intercept and intercept times"], Watkins-Johnson Tech-notes Vol. 3, No. 3, May/June 1976</ref>