ASYMPTOTIC ANALYSIS OF MUTUAL COUPLING IN CONCAVE CIRCULAR CYLINDRICAL ARRAYS .2. NEAR-ZONE

This paper evaluates the near-zone coupling coefficients in large conc ave 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 asymptoti c order, to those in an equivalent infinite planar array. In the trans ition region, which lies between the paraxial and the far-zone, or the ray region, two representations were developed: one, a transition fun ction, expressed in terms of a canonical integral which must be numeri cally evaluated, the other a uniform representation, which consists of a superposition of a planar array contribution and a few periodic str ucture rays. The uniform representation is valid in the near-zone (whi ch 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.