Abstract: An image sorting system such as an airborne defense system for receiving and classifying enemy radar signals according to frequency, azimuth angle of arrival, etc. It employs a RAM that is addressed by the frequency and azimuth values of each received signal. If the addressed storage location in the RAM is empty, a number is assigned and stored there to represent the radar that is producing the received signals. The RAM represents a map of the aircraft's environment. Hash addressing, chaining of overlapping radar signals, pipelining to facilitate the blocking of superfluous pulse Doppler signals, etc. enable rapid reliable sorting and identification of hundreds of radar or other signals in the area.

Abstract: The angle of arrival (.theta.) of an RF signal is determined using only two widely spaced antennas (A, B). A coarse/fine measurement system (40) is disclosed wherein the actual time delay between zero-crossings responsive to the same RF carrier cycle within the pulse envelope arriving at each antenna is determined. There is no need for additional antenna pairs with different baselines to otherwise resolve ambiguity.

Abstract: A signal to be measured is limited and supplied to the clock inputs of a series of high speed D-Flip-Flops. The D input of the Flip-Flops are simultaneously supplied with signals from a Clock by way of taps on a Delay Line. The state of the Flip-Flops accurately represent in digital form the time of occurrance of selected leading edges of the signal to be measured with a resolution of one nanosecond. Each such time of occurrance measurement is substracted from the previous measurement to determine the period of the signal to be measured. The resulting period data is stored and scaled, making it available to precisely reproduce the received signal in frequency and phase in one half cycle period steps.

Abstract: Apparatus and method for digitally encoding the frequency and pulse width of a pulse RF signal whereby the pulse is divided into a series of contiguous sampling periods within which the RF frequency is measured and recorded. The pulse width and frequency characteristics including FM and chirp content are encoded using a minimum number of digital bits.