Electro-Optics - Applied Optics Fundamentals and Device Applications - page 8

x

γ

d

θ

z

I 1 I 2 I 3 I 4 I n

y

I n = A n e ja n

FIGURE 2.3
Excitation current relationship of a linear phased array.

arranged along the z -axis. Following the analysis in Stutzman and Thiele [9],
the current in each element is represented as

− ia n

I

0 =

A e
n

(2.1)

The array is of linear phase if the elements are phased so that

a = − Bz cos θ (2.2)

n n

It follows from Figure 2.3 and Equations 2.1 and 2.2 that if the phase of
each element is changed with time, the direction of the main beam θ is
scanned. The ability to alter the direction of the main beam electronically
provides the radar designer with a myriad of scanning options from which
to choose.
A typical phased array radar configuration is shown in Figure 2.4, with
a typical conventional radar system block diagram for comparison shown
in Figure 2.5. All of the functional areas outlined in Figure 2.5 are main-
tained by the phased array system, but the distribution of duties has been
modified. The T/R modules perform several functions that are taken care
of in the beam steering, transmission, and reception functional areas in the
generic radar system of Figure 2.5. The array processor performs the func-
tions of the processor in Figure 2.5 as well as handles some of the demodula-
tion and detection functions that were performed by the receiver. The signal
generator in Figure 2.4 is accountable for the transmitter duties that are not
carried out by the T/R modules. The array controller in the phased array
configuration generates the phase shifting and transmits/receives switch-
ing information required by the T/R modules, and for controlling the signal
generator and array processor. In addition, the array controller converts the