A new type of alternating code for incoherent scatter measurements

An alternating code set is employed as one of several possible techniques used in incoherent scatter radar transmissions to obtain ambiguity-free measurements of autocorrelation functions or spectra with good range resolution. An alternating code set consists of several codes; typically, each successive radar pulse is modulated with a different code in the sequence. This technique is useful in other types of radar transmissions when the target is overspread, assuming the targets have certain statistical properties. Code sets for a new type of alternating code are presented for code lengths 8-12. This new type of alternating code differs from the first kind in two ways: it is subject to a slightly different condition for the elimination of ambiguity, and it is not restricted to lengths that are powers of 2. The new lengths are useful because they allow greater freedom in designing a multipurpose radar waveform best utilizing the available duty cycle of the radar. The alternating code technique is described in detail sufficient to allow an understanding of the two types and to show that the new condition for ambiguity-free measurements is a useful one. A search program was used to find the new sets; the aspects of the program important for decreasing the size of the search space are described. The code sets are presented, and their significance and uses are discussed.