On Minimizing the Backscattering by Optimization

It is often suggested to minimize the backscattering from a finite array by a computerized optimization process. (Some people will go to great length to avoid any involvement with the physics of their problem. Some have no choice.) 

While such an approach is feasible, it should be applied with great care. A very simple example will illustrate what can easily go wrong and undetected by operators whose intellectual capacity is limited to comparing numbers. In Fig. 5.37a we show the typical backscattered fields in vector form from each triad similar to the case in Fig. 5.8. Recall that the fields scattered from the two edge triads are quite different from the rest if all the triads are loaded with identical load resistors Rl- This was simply because the terminal impedances of the edge triads were in a different element environment, resulting in terminal impedances different from the rest. 

When applying a computerized approach, we would most likely calculate the total backscattered field—that is, the sum of the triad fields. Typically a computer would then in all likelihood find the simple solution shown in Fig. 5.37b. By variation of the identical load impedances Z, the computer would produce a 

A better solution is shown in Fig. 5.37c. Here the fields from each triad have been forced to be zero by the process discussed earlier in this chapter. It does not rely on simple cancellation and will consequently be more broadbanded and less sensitive to angle of incidence. 

Oh yes, there is more to design than just run a computer, or worse yet, let the computer run itself without any interference from the human brain. 

---