Linear patch array pattern degradation due to corporate feed radiation
A specific linear array of square patches is considered. The array, measured feed radiation, and sources of feed radiation are examined. It is shown that radiation from a coplanar microstrip feed network can degrade the patterns of a linear patch array to an extent that is unacceptable in many applications. The problem arises when the microstrip substrate parameters are chosen to maximize radiation at the patch edges, thus undermining the ability of the feed network to guide waves. One solution is to use a relatively thin, high-relative-permittivity substrate. This has the disadvantage of reduced bandwidth. Another approach is to sacrifice the low-cost coplanar feed by placing the feed on the opposite side of the ground plane from the radiating elements, and using coaxial pins to drive the patches. In this way, the radiation and guided wave functions are separated and the substrate parameters can be separately optimized for each. The feed can also be screened.