Abstract: An array antenna is located on an upper surface of a vehicle. The array antenna is oriented at a right angle to a radio wave blocking obstacle existing in a radio wave transmission path. A diffracted wave is effectively received at the shadowed portion where a direct wave is not transmitted because of the radio wave blocking obstacle. If the antenna dimension of its longitudinal direction is larger than that of the radio wave blocking obstacle, both direct wave and diffracted wave are received and therefore the reception power decrease caused by the radio wave blocking obstacle is further reduced.

Abstract: A branching filter for branching two microwaves from waves having two microwaves and a plurality of milliwaves includes two groups of coupling holes fluidically connected to one or more band-pass filters and a branching waveguide, one group of coupling holes being arranged on the wall of the conical horn so as to be equiangularly disposed thereabout with a 90.degree. interval defined between adjacent coupling holes when, for example, four coupling holes, filters, and waveguides are employed in such group, while the second group of coupling holes, disposed axially downstream of the first group of holes by means of a predetermined distance, is similarly disposed about the horn although angularly offset with respect to the holes of the first group through means of an angle of 45.degree..