| abstract |
A plurality of insulators are disposed in holes, respectively, defined in a metal plate of a waveguide of a circularly-polarized-wave flat antenna. Each insulator has a through-hole and a protrusion. The through-hole extends from the outside of the metal plate to the inside of the waveguide. The protrusion protrudes outward beyond the metal plate. The protrusion has a groove which is open to the outside. Curl antenna elements each have a shaft portion, an arm portion, and a curl portion. The shaft portion is fitted in the through-hole of the insulator and partly protrudes outward from the metal plate. The arm portion extends from the protruded end of the shaft portion. The curl portion is in a substantially helical shape and connected to the top of the arm portion. When the arm portion is engaged with the groove of the insulator, provided that the position of the groove of the insulator has been set in accordance with a desired orientation of the curl portion of the curl antenna element, the orientation of the curl portion is automatically set to a predetermined direction. Thus, the orientation of the curl portion can be precisely set to the predetermined direction. As a result, the operation for mounting a large number of curl antenna elements on the insulators in different directions according to the positions thereof can be easily performed. |