Two Dimensional Phased Arrays
In this section, we'll look at two-dimensional or planar arrays with uniform spacing and with
phased weights. Fortunately,
two-dimensional phased arrays are not much more difficult to understand than one-dimensional arrays.|
In one-dimensional arrays, the weights are chosen to compensate for the phase propagation of a wave in a desired direction. The extension to two-dimensional arrays is straight forward. Lets assume we have an array in the (x,y) plane, with positions given by:
This array is plotted in Figure 1.
Figure 1. Array geometry for two-dimensional (planar) array.
The phased weights for a two-dimensional planar array steered towards are given by:
In the above equation, the weights are designed to steer the array towards the wave vector in the desired direction, written as .
To illustrate this, we'll assume the array is steered to broadside - . In this case, all of the weights simply become equal to unity (1.0). The array factor becomes:
Applying the sum formula twice, the above reduces to:
To plot this function, we'll introduce simplifying variables, u and v:
The above variables are often used in plotting two-dimensional patterns, and are known as directional cosines. A plot of the AF above is shown in Figure 2:
Figure 2. Magnitude of AF for two-dimensional array described above.
As expected, the array is maximum when (u, v)=(0,0), which corresponds to the desired direction .
Antenna Weighting Page