Communications, Radar & Electronic Warfare (201.. - Index of

122Communications, Radar and Electronic Warfare/ [ Element/Array faceAdvancmg wavefrontfrom a targetTime of arrival differencebetween elements= phase differenceFigure 7.22 A waveform arrivIng at the face of a phased array. The advancIng waveform hit, the topelement fir,t SInce It IS the closest. The wavefront then reaches each indIvidual vertical element with afixed time (or more importantly, pha')e) delay.The total coverage of the radar is Ii mi ted by the abi I ity to steer the beams to the edgeof the coverage area.The beamforming of the phased array is illustrated in Figure 7.22. This shows awavefront arriving from a specific target at an angle in the vertical direction. Thewavefront first arrives at the top element first, followed by all the others, with anadditional time delay per element based on the perpendicular distance difference asshown. The time difference is small enough for the delay to be considered as aphase delay.Calculation of the delay time allows beamforming for both the transmit andreceive signals. This is illustrated in Figure 7.23, which shows the system inreceive state.Phase delays are used in the con'elation process to generate beams. Addingsuccessive delays to inputs across a plane of the array directs the beam in the desireddirection, and the line of sensors in the array acts to focus the beam to the desiredbeam width in that plane. Waveforms arriving from different directions are not