Abstract: A method of operating a multibeam radar carried on a platform flying a mission over a prescribed flight path to obtain images of a plurality of target areas, the beams of said radar being the result of respective transmit pulses and beam returns being received by respective receive windows. A range of pulse repetition frequencies and pulse repetition frequency change rates are used in an iterative process to determine non-collision alignments of any combination of transmit pulses and receive windows. When a non-collision alignment is determined the particular arrangement producing that non-collision alignment is used in a simulated flight of the platform to determine dwell time before a collision occurs. An arrangement that produces sufficient dwell time to accomplish a mission is then used in an actual flight of the platform.

Abstract: A coherent signal generated at a precise frequency determined by an atomic clock is transmitted by a moveable object. A receiver station compares the frequency of the coherent signal received from the moving object with a second coherent signal generated at the same precise frequency by an atomic clock in the receiver to determine the radial component of the velocity of the moveable object relative to the receiver as a function of the doppler shift of the transmitted signal. Low cost, low power, miniature atomic clocks with an accuracy of 10.sup.-11 make possible accurate measurements of velocities of only centimeters per second. Such velocity measurement can be used to enhance radar tracking in air traffic control and collision avoidance systems.

Abstract: A secondary radar uses monopulse reception techniques to improve the estimate of the aircraft position and to improve the reliability of the reply decoding process. Digital signal processing techniques are utilized to replace the analog circuit used in the prior implementations. The secondary radar implements monopulse processing using a half angle phase method wherein the sum and difference signals are encoded in a complete phasor. The detection of the signal and extraction of the azimuth angle data is implemented using a digital receiver concept. The complex phasor is sampled at an intermediate frequency, down converted to baseband and detected. The azimuth angle is computed using arithmetic methods implemented by digital signal processing circuitry.

Abstract: A defruiter for filtering fruit replies from a reply data signal in a radar system. The defruiter includes a window memory, a main memory, a counter and a main defruiter. Another version of the defruiter includes the items listed above and, additonally, a data memory and a buffer. The window memory stores reply data for a number of range intervals and a number of pulse repetition times. The main memory provides and receives reply data to and from, respectively, the window memory. The counter determines the number of replies occurring in a number of range intervals and a number of pulse repetition times. The main defruiter allows reply data to be provided to a data processor of the radar system when a reply occurs in the center part of the window memory and when the number of replies determined by the counter is greater than or equal to a window parameter. The number of fruit replies occuring within the reply data supplied to the data processor of the radar system is therefore reduced.

Abstract: A system and method for detecting and removing specular multipath reports from terminal ATCRB systems for aircraft targets having Mode 3/A transponder reporting capabilities. Reports are delayed for a first time, or azimuth, interval to determine whether the report is multipath or to identify future occurrences of multipath reports. After the first azimuth interval, the report is released for display and a fragment of the report is retained for an additional azimuth interval. Of two reports with matching Mode 3/A code, the one with the greater range is considered to be a multipath reply. If the multipath report range falls within a multipath range interval and has not been released for display, it is discarded by the system as an erroneous report.

Abstract: A method and apparatus for prefiltering received target and fruit replies to filter out more obvious occurrences of fruit replies in an air traffic control system. A detector detects reply signals occurring during sweeps of a radar. After each sweep of the radar, the sweep interval is scanned for the occurrences of reply signals. If a received reply is repeated in any of a predetermined number of successive sweep intervals, then standard sequential observer detection is performed on a larger predetermined number of beam sweeps. If, however, the received reply is not repeated in any of the beam sweeps of the first window, then the signal is considered to be a fruit signal and is discarded.