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Fourier Transforms in Radar And Signal Processing_8

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Tham khảo tài liệu 'fourier transforms in radar and signal processing_8', công nghệ thông tin, kỹ thuật lập trình phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Equalization 141 Figure 6.7 Array response with equalization a five taps 20 oversampling and b four taps 50 oversampling. 142 Fourier Transforms in Radar and Signal Processing Figure 6.8 Sum beam frequency response effect of bandwidth a 10 bandwidth and b 200 bandwidth. Equalization 143 equalization and the dotted response is that for the case of only integer delay compensation in units of the sampling interval . In Figure 6.8 a this curve is identical to the dashed curve as all the delays are within 0.5 sampling intervals so no integer compensation is feasible. We note that with the same set of parameters the response is essentially independent of the fractional bandwidth the shapes of the responses are virtually identical. In the second case the sampling rate is much higher of course in this case as the bandwidth is 2fo where f0 is the center frequency the sampling rate is 2.4f . To sample at this rate may be impracticable at radar frequencies but may well be feasible for sonar where broadband or even wideband operation is much more commonly required and the actual signal frequencies are much lower. The fact that these responses are very similar is not a coincidence but illustrates the fact that the response is essentially independent of the fractional bandwidth and only depends on how well the delays are matched. This depends for a given set of equalization filter parameters m and q on how close the required delays are to integer multiples of the sampling period. This will vary in general from one element to another and will depend on the beam steered direction and the element separation. In particular cases the delays required may all be integral in sampling periods in which case the matching will be exact in principle and the response will be completely flat. At the other extreme the delays required might all be half-integral which is the worst case for matching. In general however there will be a spread of delays and the performance will be intermediate. This