Annular microstrip antenna element and radial line antenna system employing the same

A radial line antenna system comprising:

• a radial waveguide including a pair of conductor plates situated opposite to each other with some space there between, the space being small relative to a wavelength of an electromagnetic wave to be transmitted, for transmitting the electromagnetic wave from a central part of the radial waveguide to a peripheral part of the radial waveguide,
• a plurality of annular microstrip antenna elements formed on an outer surface of one of the pair of conductor plates, said plurality of annular microstrip antenna elements are disposed having equal spaces between them,
• connecting means for connecting the annular microstrip antenna element and the radial waveguide by electromagnetic coupling,
• feeding means for connecting the coaxial transmission line and the radial waveguide by electromagnetic coupling, wherein
• the annular microstrip antenna element comprises,
• (a) a dielectric layer,
• (b) a ground conductor plate mounted on one surface of the dielectric layer,
• (c) an annular radiant conductor plate formed on the other surface of the dielectric layer so as to surround an area which is symmetrical with respect to a predetermined reference line on the surface of the dielectric layer,
• (d) a feeding point located on the reference line, and
• (e) a pair of microstrip lines mounted within the area in a symmetrical manner with respect to the reference line, for connecting the feeding point to two connecting points on an inner edge of the annular radiant conductor plate.