Asymptotic analysis of mutual coupling in concave circular cylindrical arrays. II. Near-zone

For pt.I, see ibid., vol.41, no.2, p.121-36 (1993). This work evaluates the near-zone coupling coefficients in large concave arrays. A canonical model of a circular cylindrical concave array of open-ended rectangular waveguides is analyzed. It is shown that in the paraxial region (which also includes the area close to the excited element) the coupling coefficients are identical, to lowest asymptotic order, to those in an equivalent infinite planar array. In the transition region, which lies between the paraxial and the far zone, or the ray region, two representations were developed: one, a transition function, expressed in terms of a canonical integral which must be numerically evaluated, and the other a uniform representation, which consists of a superposition of a planar array contribution and a few periodic structure rays. The uniform representation is valid in the near zone (which includes both the paraxial and the transition region) as well as in the far zone. This form is simple and may be immediately generalized to concave arrays with slowly varying curvature and periodicity