Microwave directional antenna employing surface wave mode

Claim 1

A microwave directional antenna, comprising: a flat circular metallic ground plate (6) having a flat surface with a central circular opening therein, said ground plate having a circular outer wall extending axially outwardly from said flat surface, a flat circular disc (1) of dielectric material lying over and in contact with said flat surface of said ground plate, said disc covering said central opening and having an outer flat surface facing away from said flat surface of said ground plate, said disc covering said opening and extending to said wall of said ground plate; a hollow circular waveguide (5) made of metal and connected to said ground plate, said hollow waveguide having a central passage communicating with said opening of said ground plate for supplying microwave radiation to said disc; a metal transition member (4) connected to said disc at a center of said disc and overlying said opening of said ground plate for changing a mode of propagation of microwave radiation from said waveguide to said disc; and a plurality of line discontinuities (2) at least at said outer flat surface of said disc, said discontinuities lying in a plurality of concentric radially spaced rings in said outer flat surface of said disc, said rings being radially spaced by an equal selected spacing (d) to effect a radiation characteristic for microwave radiation propagating radially through said disc whereby microwave radiation propagating radially through said disc is deflected to radiate axially from said disc upon approaching said discontinuities.