Dual frequency circularly polarized microwave antenna

A microwave antenna operable at two different frequencies simultaneously, comprising:

• (a) a first substantially planar dielectric layer having a top face and a bottom face;
• (b) a substantially planar, square conductive radiating patch mounted on the top face of the dielectric layer, having a center and two coplanar diagonal axes passing through the center;
• (c) a first substantially planar conductive ground plane abutting the bottom face of the dielectric layer, having first and second elongated apertures which intersect each other at their respective midpoints and which are positioned orthogonal to each other, the ground plane being positioned such that the midponts of the apertures are aligned with the center of the patch along an axis that is perpendicular to both the patch and the ground plane, and each of the apertures is parallel to one of the diagonal axes of the radiating patch;
• (d) tuning means electrically connected to the patch for converting two linearly polarized orthogonal field mode signals into circularly polarized signals and vice versa;
• (e) a second substantially planar dielectric layer having a top face contacting the ground plane, and a bottom face;
• and
• (f) a third substantially planar dielectric layer having a top face and a bottom face, with a first conductive planar feed network attached to the top face, and a second conductive planar feed network attached to the bottom face, the top face of the third dielectric layer being attached to the bottom face of the second dielectric layer;
• wherein
• the first feed network is symmetric about a first center plane which is orthogonal to the ground plane, to the radiating patch, and to the third dielectric layer, and which bisects the first aperture, said first feed network comprising at least two elongated substantially identical parallel conductive microstrip elements positioned equidistant from the first center plane, the microstrip elements being positioned so as to orthogonally intersect a projection of the first aperture onto the plane of the third dielectric layer in at least two distinct locations;
• and
• the second feed network is symmetric about a second center plane which is orthogonal to the ground plane, to the radiating patch, to the third layer, and to the first center plane, and which bisects the second aperture, said second feed network comprising at least two elongated substantially identical parallel conductive microstrip elements positioned equidistant from the second center plane, the microstrip elements being positioned so as to orthogonally intersect a projection of the second aperture onto the plane of the third dielectric layer in at least two distinct locations.