A new radio direction-finding (DF) technique which applies matched-filter theory to the DF problem is presented. The new technique, called Matched-Filter Doppler Direction Finding (MFD DF) is based on the doppler DF principle in which a rotating antenna, or its equivalent, superimposes periodic frequency modulation on the received carrier. The phase of the induced modulation contains information on the angle of arrival. It is shown that a bandpass filtering operation, which satisfies the phase-matching requirement of a matched filter, converts the frequency-modulated signal to an amplitude-modulated signal whose envelope is a periodic narrow pulse with no sidelobes. The relative time of occurrence of the pulse is a measure of angle of arrival. Included is the description of and results obtained with an experimental system used to confirm the analytical results, to study the effects of noise, and to explore alternatives available in the design of an operating system. Encouraging results were obtained using this same experimental system with a conventional operating doppler DF set. (Author)This task was supported by: Naval Ship Systems Command (Code 6050)http://archive.org/details/theoryperformanc00orej