Compact antenna for circular polarization

Claim 1

A compact antenna for circular polarization comprising: a substrate made of a dielectric material and having a top surface and a bottom surface; a ground plane on the bottom surface of said substrate; four planar and rectangular patches made of an electrically conductive material and defined as first, second, third and fourth patches which are mounted in a coplanar relation on the top surface of said substrate, the lengths of said rectangular patches being substantially equal, the widths of said rectangular patches being substantially equal, said four patches being arranged in a square pattern such that a longitudinal axis of said first patch extends parallel to that of said third patch and perpendicularly to that of each of said second and fourth patches, and that each said patch is separated from two adjacent patches by a distance, said square pattern having four sides each of which is equal to the sum of said distance, length and width of said rectangular patch; shorting means for shorting each of said four patches to said ground plane at a shorting point which is located at a corner of said patch; and feed means for directly feeding only each of said first and second patches at a feed point located near said shorting point, thereby defining said first and second patches as active antenna elements and defining said third and fourth patches as parasitic antenna elements, said feed means comprising a 90° hybrid circuit for providing a first signal to said first patch and providing a second signal which is 90° out of phase with said first signal to said second patch, and two feed lines extending from said 90° hybrid circuit to said feed point of each of said active antenna elements through said substrate without interfering with said parasitic antenna elements, said parasitic antenna elements being electromagnetically excited by said active antenna elements fed with said first and second signals to develop third and fourth signals which are cooperative with said first and second signals to achieve circular polarization, said third patch providing said third signal which is 180° out of phase with said first signal, said fourth patch providing said fourth signal which is 270° out of phase with said first signal, all of said first, second, third and fourth patches operating at a single resonance frequency for transmitting a circular polarization wave.