Abstract: A ground based radar antenna system and method for determining the elevation angle .phi. of a tracked target having a shaped reflector and a pair of spaced feedhorns for transmitting radiated energy to and receiving returned signals from the tracked target T, the shaped reflector and feedhorns cooperating to increase the range of coverage of the elevation angle .phi. beyond the coverage previously available with a standard parabolic reflector and to increase the gain of the signals returned to the ground based radar antenna system while simultaneously eliminating elevation angle ambiguities over prior systems employing only feedhorns for collecting returned signals. The radar system includes a construction which approximates a cosecant-squared antenna pattern, permits the calculation of the target height and three-dimensional position, and is economical to manufacture.

Abstract: A terrain height radar system and processing method comprising a high resolution synthetic aperture radar (SAR) mounted on an air vehicle and a SAR signal processor containing a signal processing algorithm or method for computing terrain height and radar backscatter power. The system contains motion sensing and navigation functions that also provide data to the signal processor to provide motion compensation. Signal processing algorithms in the method compensate for planar motion of the air vehicle for variations of terrain height in the field of view. The algorithms also compensate for nonplanar motion of the radar, and for scatterers in or very near to a reference plane in the field of view. The algorithms exploit defocusing due to displacement from the reference plane to estimate the terrain height above the reference plane. The algorithm is computationally efficient because the bulk of the radar signal processing is common to both the SAR function and the terrain height estimation function.

Abstract: The calibration apparatus (16) includes a recirculating optical delay loop (22) constituted by two delaying fibers (F2, F3), an optical amplifier (28), and a coupler (26) for providing a succession of a plurality of delayed optical signals (OR) in response to a single initial signal (OA). The invention is particularly to radars.

Abstract: It is determined that an altitude of a vehicle can not be calculated from data applied from satellites. When the calculation can not be performed, a provisional altitude is obtained with a following equation:H=(1-.alpha.)H.sub.G +.alpha.H.sub.Owhere H.sub.G is an altitude obtained by the GPS, H.sub.O is a reference altitude obtained by the outside means, .alpha. (O<.alpha.<1) is a predetermined smoothing coefficient.

Abstract: Radar apparatus for determining the height of a low-elevation target, the target being illuminated by a transmitter (7) and an antenna (3) via a TR-switch (6). Electromagnetic radiation reflected directly by the target and indirectly by the target via the earth surface is received by the antenna (3) and processed in a sum receiver (9, 10, 11), connected via the TR-switch (6) to the antenna (3), into complex sum signals, and in a difference receiver (12, 13, 14), into complex difference signals. A signal processor (15), receiving the complex sum signals and the complex difference signals, is provided with an algorithm which determines the height of the target. The algorithm enables the determination of the target height while the antenna remains directed at the target.

Abstract: A range dispersion sensor operative to detect objects of a preselected height "h" operates on quarterwave interference principles. Electromagnetic energy is modulated at a first frequency f.sub.1 such that objects of the preselected height h disposed upon a background create a quarter-wave length reflector. A beam of electromagnetic energy reflected from an object of height h and its proximate background interferes destructively to create a null signal. Effects of non-uniform reflectivity are normalized by modulating the beam at a second frequency f.sub.2 selected to not create constructive or destructive interference effects with objects of the preselected height. The ratio of the two signals is taken thereby normalizing the effects of non-uniform reflectivity, and the resultant ratio is indicative of the height of the objects.

Abstract: A radar having a multiplicity of receive beams stacked in elevation and a target height extractor especially for use therein are disclosed. In operation, a set of range sweeps corresponding to an azimuth scan of the stacked receive beams across a detected target is established. A range cell interval corresponding to the detected target is estimated for each range sweep of the set. A target range measurement is computed from a set of estimated range intervals. Only the radar receive beam echo information corresponding to the estimated range cell interval for each range sweep of the established set is used by the height extractor to compute a corresponding set of elevation angles. A target elevation angle is formed as the weighted average of this computed set. Only one height computation is performed for each established set of range sweeps based on a function of factors including the computed target elevation angle and computed range measurement of the corresponding established set of range sweeps.