Synthesis of multilevel and binary sequences with good correlation properties

Abstract

In radar systems the very low side lobes that can be achieved with amplitude and phase modulated pulse trains especially particularly in systems requiring a large dynamic range. Moreover, the excellent self-clutter rejection performance is obtained without sacrificing the ability for the separation of close targets (no main lobe widening). The additional expense of encoding and decoding in amplitude and phase may be justified for radars that must cope with land clutter or operating in a dense-target environment. To choose a suitable transmit waveform is an important problem in radar design. This is so because, the waveform controls resolution, clutter performance and also bears heavily on the system cost. Theoretical studies which provide the basis for technical advances have not so far solved the general signal design problem. The knowledge about the properties of the pulse trains shows that, a class of signals particularly well suited to digital processing of increasing practical importance. Two properties of such sequences are of interest. One is the energy ratio (ER) defined as the ratio of the total energy of the sequence to the energy of the largest pulse. The other property is the total side lobe energy (SLE) which is the energy in the side lobes of the autocorrelation function of the sequency. The work presented in this research is mainly concerned with the synthesis of multilevel and binary waveform of any desired length that has high energy ratio and low side lobe in their autocorrelation function (ACF). For the design of multilevel sequences in iterative technique is proposed, this techniques employed the properties of optimum inverse filtering and shown to be effective for the generation of multilevel sequences in any desired lengths. The method of clipping proposed in this research converts a multilevel sequence to binary sequence in same lengths while it is still retaining at low side lobe in autocorrelation function. It is shown that the iterative method based on inverse filtering and the method of clipping provide effective techniques for the generation of multilevel sequences that have high energy ratio and low side lobe energy in their autocorrelation function. Such sequences can then be effectively used to improve the range and Doppler resolution of radars.