A linearly polarized antenna includes a
dielectric substrate, a ground conductor which is overlapped on one surface of the
dielectric substrate, an
antenna element made of linearly polarized, which is formed on an opposite surface of the
dielectric substrate, a plurality of
metal posts in which one end side of each of the plurality of
metal posts is connected to the ground conductor, the plurality of
metal posts piercing through the
dielectric substrate along a thickness direction thereof, another end side of each of the plurality of metal posts being extended to the opposite surface of the
dielectric substrate, the plurality of metal posts being provided at predetermined intervals to form a cavity so as to surround the
antenna element, and a conducting rim which short-circuits the other end side of each of the plurality of metal posts along a line direction of the plurality of metal posts on the opposite surface side of the
dielectric substrate, the conducting rim being provided while extended by a predetermined distance toward a direction of the
antenna element, the conducting rim having, e.g., a triangular portion. In the linearly polarized antenna, generation of a
surface wave is suppressed by the cavity and the conducting rim, and the antenna can be set to the desired
radiation characteristic. Additionally, a
frequency characteristic of an
antenna gain can have a steep decline (notch) in an RR radio-wave emission prohibited band by utilizing a
resonance phenomenon of the cavity. Therefore, the linearly polarized antenna is effective in decreasing
radio wave interference with EESS or
radio astronomy service.