In a system for determining a location of an emitter, a mobile frame is configured for movement relative to the emitter. A main receiver and a frequency mixing antenna are supported on the mobile frame at different locations on the frame but so that both move with the frame relative to the emitter. The frequency mixing antenna is configured to receive an emitter signal and output a frequency-mixed signal. The main receiver is configured to directly receive the emitter signal and receive the frequency-mixed signal. A processor is configured to determine a first Doppler frequency from the direct emitter signal and a second Doppler frequency from the frequency-mixed signal and to determine the location of the emitter in a defined search area based on the first and second Doppler frequencies. Multiple Doppler frequencies can be created also using multiple frequency mixing antennas to improve the localization resolution.