  This letter presents a recursive technique to synthesize the array factor
(AF) of a concentric ring array. In this method, first, the problem is modeled
using the traditional least square method (LSM). In the second step, a
recursive technique is applied to the defined problem. It is shown that for
many practical ring arrays, only a few iteration number is sufficient to obtain
a solution with high accuracy. To evaluate the performance and benefits of the
proposed method, various concentric ring arrays with different array factor,
including equi-ripple pattern, pattern with deep nulls, flat-top array factor,
are examined. It is shown that the introduced procedure is a very noble
candidate for this purpose.
