Page 203 - Fundamentals of Radar Signal Processing

somewhat less for very short duration sequences (M < 10) but varies little for

larger M.

FIGURE 3.15 Maximum off-peak Doppler spectrum sampling loss for a
sinusoidal slow-time signal sampled at κ M samples per Doppler spectrum
period.

3.3 Sampling in the Spatial and Angle Dimensions

As discussed earlier, two distinct types of spatial sampling are of concern in a
radar system. One type concerns the design of phased array antennas. A phased
array samples the incoming wavefront at the individual array element locations.
Thus, the spacing of these elements must be chosen to adequately sample the
wavefront for any incidence angle. The second concerns beam steering.
Mechanically or electronically steered antennas can change the pointing

direction of their antenna beam. As the beam is scanned to search or map a
region in space, a decision must be made as to how far it is permissible to scan
before another pulse (or burst of pulses) must be emitted by the radar so that the
external environment is adequately sampled. The next two subsections address
these questions.

3.3.1 Spatial Array Sampling
Chapter 1 introduced the concept of spatial frequency and wavenumber.

Consider a uniform linear array with element spacing d, as shown in Fig. 3.16.
The wavenumber (spatial radian frequency) of an RF signal with wavelength λ
impinging on the array antenna from a direction of arrival θ radians off the
normal to the array, as shown in the figure, is