The matching improvement achieved by using a substrate 230 with lower dielectric constant than that of the substrates used in the other elements for the corner element 200a is further demonstrated by comparing FIGS. 7A and 7B. FIGS. 7A and 7B are Smith charts showing the simulated self-match (solid lines 322, 332) versus the simulated total mutual coupling signal (dashed lines 324, 334) for examples of the sub-array 110 of FIG. 4. FIG. 7A shows data of the corner element 200a for an example of the sub-array 110 in which all six antenna elements 200 were simulated with the substrate 230 having a dielectric constant of 3.0 (corresponding to the simulation data presented in FIG. 3). FIG. 7B shows data of the corner element 200a for an example of the sub-array 110 in which five of the six antenna elements 200 (elements 1-5) were simulated with the substrate 230 having a dielectric constant of 3.0 and the corner antenna element 200a (element-6) was simulated with the substrate 230 having a dielectric constant of 2.4 (corresponding to the simulation data presented in FIG. 6). As can be seen with reference to FIGS. 7A and 7B, the use of a lower dielectric constant substrate applied at the corner element 200a can reduce the self-return signal of the corner element, manifested by the size reduction of the impedance locus 332 in FIG. 7B in comparison with 322 in FIG. 7A.