| Phased array antennas consist of multiple stationary antenna elements, which are
fed coherently and use variable phase or time-delay control at each element to scan
a beam to given angles in space. Variable amplitude control is sometimes also
provided for pattern shaping. Arrays are sometimes used in place of fixed aperture
antennas (reflectors, lenses), because the multiplicity of elements allows more precise
control of the radiation pattern, thus resulting in lower sidelobes or careful
pattern shaping. However, the primary reason for using arrays is to produce a
directive beam that can be repositioned (scanned) electronically. Although arrays
with fixed (stationary) beams and multiple stationary beams will be discussed in this
text, the primary emphasis will be on those arrays that are scanned electronically.
The radar or communication system designer sees the array antenna as a
component (with measurable input and output) and a set of specifications. The
array designer sees the details of the array and the physical and electrical limitations
imposed by the radar or communications system, and within those constraints
seeks to optimize the design. This chapter is written from the perspective of, and
for, the system designer. The remainder of the text discusses array design issues. |
