Digital signal processing in airborne radar

Abstract

My introduction to the real world of radar digital signal processing occurred in 1959. Our airborne radar design team at General Electric had contracted to design and produce an advanced airborne surveillance radar for the U.S. Navy Hawkeye aircraft (E2A). The design concept called for the integration of the radar return signals to be done digitally. The signals from the analog “front end” of the radar were passed through a threshold detector, and the single-bit stream at a rate of 5 MHz was to be integrated in a range azimuth organized digital memory to enhance the radar sensitivity. The signal processing algorithm was the essence of simplicity; however, the primitive memory technology presented formidable hardware design challenges. A rotating magnetic drum with multiple track recording heads was the only available memory technology that could operate at a bit rate of 5 MHz. The spacing between the recording heads and the surface of the drum had to be maintained at a few mils in order to achieve the necessary bandwidth. Simultaneously, the drum rotation had to be synchronous with the radar trigger in order to hold the range registration over the integration period. All of this magnetic drum control had to be accomplished in the vibration and shock environment of a carrier-based aircraft. Magnetic core memory technology matured during the early 1960s and provided a welcome relief from the limitations of the magnetic drum in performing the noncoherent pulse amplitude integration function. However, the other necessary radar signal processing functions (surface clutter filters and pulse compression filters) were still analog. The real momentum in the application of large scale digital signal processing to airborne radar sys-