Page 289 - Fundamentals of Radar Signal Processing

weighting result but with some differences in details of the sidelobe structure.

The peak is reduced from 60 to 54.64 dB with weighting, a nearly identical LPG
of 5.36 dB. The peak sidelobe of the weighted response is 40.7 dB below the
corresponding mainlobe peak, 3.5 dB better than the frequency-domain case.
The Rayleigh width has increased 97 versus 93 percent in the frequency domain
weighted case. This is consistent with the better sidelobe performance of the
time-domain case. Additional detail on frequency- and time-domain weighting

of LFM waveforms is available in Richards (2006).

FIGURE 4.36 Comparison of the receiver filter output with (black curve) and

without (gray curve) time-domain Hamming weighting of the matched filter. See
text for details.

4.7.3 Waveform Spectrum Shaping
The principal limitation of the receiver weighting approach to range sidelobe
control is that the resulting filter is not matched to the transmitted waveform,
resulting in an SNR loss. An alternative approach is to design a modified pulse
compression waveform whose matched filter output inherently has lower
sidelobes than the standard LFM. The waveform should be designed to have a

spectrum shaped like that of a window function with the desired sidelobe
behavior. Such a waveform would combine the maximized SNR of a truly
matched filter with low sidelobes. There are two common ways to shape the
spectrum. Both start with the idea that the LFM spectrum’s relatively square
shape is the result of a linear sweep rate combined with a constant pulse
amplitude, resulting in a fairly uniform distribution of the signal energy across

the spectral bandwidth. The spectral energy could be reduced at the edges,
giving a “window-shaped” spectrum, by reducing the signal amplitude at the
pulse edges while maintaining a constant sweep rate, by using a faster sweep