Why Radar Shows Ghost Targets

A multi-million-dollar radar can plot an enemy jet 10 km away that is not actually there — a "ghost target" conjured by range ambiguity. Starting from that failure we rebuild radar from an echo and a stopwatch: the five-block set and the duplexer, R = c·t/2 and the PPI, the two physical walls (Rmax from PRF and the blind range from pulse width), the slant-range and resolution traps, and why detection ultimately hinges on the radar equation and aspect-dependent RCS.