Log-periodic array of dual-mode patch elements

The antenna presented is an LP (log-periodic) array of dual-mode patches that offers improved performance in a reduced size. A rectangular patch of high aspect ratio is used. This patch is excited simultaneously in two modes from the same feedline, a microstrip line on the opposite side of the ground plane from the patch. A constant-field mode is driven by the capacitively loaded post, which is connected at its base to the microstrip line and is centered under the patch. The post passes through the ground plane in the center of a rectangular slot that serves also to excite the TM/sub 01/ mode. The first array was designed to have a structure bandwidth of two. A scale factor of tau =0.9 was chosen on the basis of the desired overlap of the loading effect of several adjacent elements. The measured S/sub 11/ data (referenced to 50 Omega ) for the array are shown. The operating band of the antenna (1.03 GHz to 1.75 GHz) is reasonably less than the structure bandwidth. Wideband performance at a high-efficiency level has been obtained.<>