A Phase-Channel Combiner, Mod. I, for the NRL Space Surveillance System

The Space Surveillance System developed at Naval Research Laboratory (NRL) for the detection of earth satellites forms a fence across the southern part of the United States. Four receiving sites are altered with three transmitting sites which iluminate satellites with radio energy as they traverse the fence. The angle of arrival of the reflected signals is measured at each receiving station by a compound radio interferometer. These signals yield a multiplicity of channels which are normally recorded on paper and analyzed manually by visual aids and special slide rules. With the increasing satellite population and the repetitive nature of their orbits, the number of fence crossings has increased considerably. Automation in the detection process is needed to facilite identification and sorting of satellites from each other (and from refuse) if a large backlog of data is to be avoided. An electronic system has been developed which automatically combines the phase channels into one unambiguous channel and depicts the angles of arrival of the radio energy from the satellites. The basic technique used in the phase-channel combiner is as follows. Since complete a priori information on the incoming signals is known, simulated signal waveforms, locally generated, are correlated channel by channel with each signal channel from the radio interferometer. At the moment of coincidence between each simulated and live signal channel, a "marker" pulse is generated. This process is applied simultaneously to all of the output channels of the multichannel radio interferometer.