Page 307 - Fundamentals of Radar Signal Processing

FIGURE 4.48 Contour plot of ambiguity function of a 13-bit Barker code.

(4.135)

This constraint limits the Doppler mismatch loss to 1 dB or less.
The limited number and length of Barker codes has led to various
techniques for constructing longer biphase codes with good sidelobe properties.
Combined or nested Barker codes form a longer code as the Kronecker product

of two shorter Barker codes. If an N-bit Barker code sequence is denoted as B ,
N
an MN-bit code can be constructed as B ⊗ B . The Kronecker product is simply
N
M
t he B code repeated M times, with each repetition multiplied by the
N
corresponding element of the B code. For example, a 20-bit code can be
M
constructed as the product B ⊗ B 5
4

(4.136)

These codes have a peak sidelobe higher than 1. The autocorrelation of the code
of Eq. (4.136) is shown in Fig. 4.49. Notice that the magnitude of the peak
sidelobes is 5, so that the PSL compared to the autocorrelation peak is only 1/4