Abstract: Failure detection in a phased array antenna system is accomplished using a cluster-oriented detection scheme and a mutual coupling test signal injection technique. RF BITE TRM (110) is connected to an RF BITE port (120) on an illuminating means (140). Illuminating means (140) provides a uniform input signal level to many TRMs (150). Each TRM (150) is connected to an antenna element (210). Controller (170) causes one element (220) in a cluster to operate in a transmit mode and causes other elements (230) to operate in a receive mode. Internal detectors in TRMs (150) are used to detect signal levels, and these detected signal levels are used to identify failure modes. This cluster search method operates well for many types of phased arrays including rectangular and triangular lattices, planar and conformal apertures, single frequency and shared aperture types.