AM/FM noise in the target illumination signal for semi-active missiles

In semi-active missile guidance, a high-power transmitter not collocated wi th the missile generates continuous wave or interrupted continuous wave ill umination that is reflected from the target to the homing missile. Noise in troduced into this illumination, which is reflected from rain, chaff, land, or sea clutter or is carried on spillover, can compete with the target ret urn. The Navy has tasked API. to specify allowable illuminator AM/FM noise and to work with its contractors to design stable oscillators and noise tes t equipment to meet these noise requirements. This article focuses on the e ffects of noise on system performance, the specification of noise requireme nts, low-noise X-band sources, and test equipment used to measure noise.