Radar search, also called radar surveillance, is the process of examining a volume of space with the objective of detecting targets in that volume. The search objectives usually include the search volume, the characteristics of the targets to be detected, and the detection requirements. The detection requirements are often defined by the probability of detection, P _D, and the probability of false alarm, P _FA, or the false alarm rate r _FA. The required P _FA may be calculated from r _FA using the techniques given in Section 6.2.

Common radar search modes include:

• Volume search, where a relatively large volume of space is searched. Volume search using rotating search radars is described in Section 7.2, and using phased-array radars in Section 7.3.

• Cued search, where a search is preformed in a relatively small volume to acquire a target whose position is approximately known. Cued search using phased arrays and dish radars is described in Section 7.4.

• Horizon search, where the radar searches for targets coming over the radar horizon. Horizon search by phased-array radars is described in Section 7.5, and by dish radars in Section 7.6.

7.1 The Search Equation

The radar detection range in a search mode, R _D, is given by general form of the radar search equation [ ^[1], p. 255]:

where:

t S	= search time;
? S	= search solid angle;
?	= target RCS;
S/N	= signal-to-noise ratio;
k	= Boltzmann's constant (1.38 10 ?23