الفهرس Only 14 pages are availabe for public view
 |  | from | 86 |  |  |
| | | from | 86 | | |
Abstract
‘amming is pro’b\ematic o radar since ie \amrcrng signa’ on\j rieeãs o xa’e one-way (from the jammer to the radar receiver) whereas the radar echoes travel two-ways (radar-target-radar) and are therefore significantly reduced in power by the time they return to the radar receiver. Jammers therefore can be much less powerful than their jammed radars and still effectively mask targets along the line of sight from the jammer to the radar (Mainlobe Jamming). Jammers also contribute to radar signals along other line-of-sights; due to the radar receiver’s sidelobes (Sidelobe Jamming). The jammer frequently remains outside the range of hostile weapons, at ranges greater than the targets it protects. Such sidelobe jammers are called stand off jammers (SOJ). When sidelobe jammers employ pulsed signals to create false targets, there signals may be rejected by using a sidelobe canceller technique. The sidelobe canceller technique is widely used in both military and civil radar to protect against receiving random pulses from near by radars that operates in the same frequency band. A sidelobe canceller technique modifies the main antenna pattern by reducing the sidelobe level (SLL). Sidelobe reduction of 30 dB and greater may be achieved .The goal of this thesis is to study one of the sidelobe canceller techniques, this techniques is based on reducing the antenna SLL by weighting the array elements. The thesis is contains two cases. The first case optimizes the array weighting in order to minimize the SLL of the linear phased array antenna without losing the beam width. The simulated phased antenna is a linear array with 8, 12 and 16 elements. Genetic algorithm (GA) has been used for the optimization process. The weights are chosen to meet any specific criteria and can be implemented using the available attenuators sensitivity. The SLL and beam width (8W) of the optimized weights are compared with those of four famous weights known as Hamming, Kaiser-Bessel, Gaussian and Blackman weights. The results show a good enhancement for the optimized weights.The second case of this thesis investigates an optimization of array weights is also investigated for the planar phased array antenna using genetic algorithms. The aim is to adjust the weight’s coefficients of the array elements to achieve a minimum.