| By means of radar, the existence or presence of an object is discovered. This is done through the release of waves from the radar transmitter and by the analysis of the returned echo through the receiver. The shorter the pulse, the more accurate the range measurement can be and the pulse energy is. Since a short pulse has a wide spectral width (bandwidth), phase modulation is a method to increase pulse bandwidth without the need to modify the pulse width. The signal is coded in a certain way prior to transmission and then compressed by a matched filter after reception; this process is called pulse compression. The pulse compression ratio equals the ratio of the width of the signal before compression to the subpulse width.; Barker codes (binary phase) are a class of binary codes whose autocorrelation or match filtering peak sidelobe is the minimum possible for a given code length. However, no Barker code greater than 13 has been found to exist. So it is vital to suppress the sidelobes to a very low minimum value so that there is no circumstance in which a strong target sidelobe masks the main lobe of a weak target.; Minimum Peak Sidelobe codes (MPS) and combined Barker codes were used and showed no improvement. Complementary sequences did not show good results because of the decorrelation of radar return signals, which prevents complete sidelobe cancellation. Both mismatched and nonmatched filters are investigated. To get satisfactory results the filter length must be long enough. This has a price of high filter hardware complexity (and consequently affects area, cost, performance, and power consumption) and great loss in signal to noise ratio. There have recently been many studies undertaken that are concerned with minimizing the complexity of the digital correlator, such as using a Two-sample sliding window adder TSSWA, which wastes a lot of the bandwidth.; Techniques will be proposed to completely remove these sidelobes or in some cases reduce them with much less circuit and no waste in the bandwidth but sometimes at the cost of SNR. |
