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  • Acronym for radio detection and ranging. 1. A radio detection system that transmits short bursts (pulses) of rf energy and detects their echoes from objects (targets) such as aircraft or ships. Note: The round-trip propagation time for the echo return may be used to determine the target's range (distance from the radar's antenna). If the transmitting antenna has a narrow beam (the usual case), the azimuth or elevation of the target may also be determined. Synonym primary radar. 2. A radio detection device that provides information on range, azimuth, and/or elevation of objects. [JP 1-02] 3. A radiodetermination system based on the comparison of reference signals with radio signals reflected, or retransmitted, from the position to be determined. [NTIA] [RR]

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  • The range that corresponds to the situation in which a radar transmitter is on and hence the receiver must be off, so that the radar transmitted signal does not saturate, i.e., does not blind, its own receiver. Note: Radar blind ranges occur because there is a time interval between transmitted pulses that corresponds to the time required for a pulse to propagate to the object, i.e., to the target, and its reflection to travel back. This causes an attempt to measure the range just as the radar transmitter is transmitting the next pulse. However, the receiver is off, therefore this particular range cannot be measured. The width of the range value that cannot be measured depends on the duration of the time that the radar receiver is off, which depends on the duration of the transmitted pulse. The return-time interval could be coincident with the very next radar-transmitted pulse, i.e., the first pulse following a transmitted pulse, or the second, or the third, and so on, giving rise to a succession of blind ranges. The blind ranges are given by rm = (mc)/(2fn), where rm is the blind range for a given value of m, m is a positive integer that indicates which of the blind ranges is being determined, c is the velocity of electromagnetic wave propagation in vacuum (approximately 3 × 108 m/s), f is the radar pulse repetition rate, and n is the refractive index of the transmission medium (nearly 1 for air). The radar blind range is independent of the radar radio frequency (rf) of the radar pulse. [From Weik '89]

  • Browse Related Terms: bouncing busy hour (BBH), FDHM, RADAR, radar blind range, radar mile, ranging, time ambiguity, Turnaround Time

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  • The volume of space that is occupied by a radar pulse and that is determined by the pulse duration and the horizontal and vertical beamwidths of the transmitting radar. Note: The radar cannot distinguish between two separate objects that lie within the same resolution cell. The radar resolution cell depth (RCD) remains constant regardless of the distance from the transmitting antenna. It does not increase with range. The RCD is given by RCD = 150d, where the RCD is in meters and d is the pulse duration in microseconds. The height of the cell and the width of the cell do increase with range. These are given by W = (HBW)(R/57) and H = (VBW)(R/57), where W is the width of the cell, HBW is the horizontal beamwidth in degrees, R is the range, H is the height of the cell, and VBW is the vertical beamwidth in degrees. The range, R, is the distance from the radar antenna to the reflecting object, i.e., the target. The width and height will come out in the same units in which the range is given. For example, if the range is given in meters, the width and height of the radar resolution cell will be in meters. The 57 merely converts degrees to radians. If the beamwidths are given in radian measure, the 57 is omitted. [From Weik '89]

  • Browse Related Terms: blanking, blinking, continuous presence, flicker, panning, quasi-lossless compression, radar resolution cell, regeneration, snow, swim, voice-operated gain-adjusting device, windowing, zooming

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