Communications, Radar & Electronic Warfare (201.. - Index of

108Communications, Radar and Electronic Warfare-- - ----Figure 7.6 Ship radar cross-section illustration before and after a missile holes the ship on the starboardside. Radar-guided missiles arriving after this hole has been created will tend to follow the first missile intothe hole.At this point we have not considered the concept that a radar will not illuminate atarget only once during a sweep. The number of successive pulses that the target will beilluminated by is dependent on the Pulse Repetition Frequency, the beamwidth in thedirection of sweep and the speed at which the antenna rotates or repeats the sweep. Fora mechanically rotating antenna, this can be expressed by:M =cp(PRF)6(RPM)cosOeOr, for a mechanically rotated antenna with a vertical as well as horizontal sweep:M = _ _ -,- F __6w" t,,(RPM)cosOewherePRF =Pulse Repetition Frequency per second.RPM =Rotation rate Per Minute.cp =o =Azimuth beamwidth in degrees.Elevation beam width in degrees.Oe = Target elevation angle.Wv =t,. =Vertical scanning speed in degrees per second.Vertical scan time in seconds (including dead time, if any).This equation is in the direction of transmission, and is only valid when cp/cos(Oe) isless than 90 degrees. Both the horizontal (left) and vertical (right) movements areshown in Figure 7.7.When the number of pulses arriving at the target is known, it is theoretically possibleto determine the probability of receiving a target when looking over the received