PURPOSE: To obtain an excellent directivity in a wide band, by filling up a cavity in such a way that plural ring-shaped wave absorbers are arranged outward from the center of a plane parallel with an antenna base, with the one having the highest frequency characteristic being put at the center.
CONSTITUTION: A cavity 3 is filled up with ring-like wave absorbers 5a, 5b, and 5c, which are arranged in the order of frequency characteristic, with the one having the highest frequency characteristic being put at the center. When such a constitution is used, radio waves radiated to the lower side are absorbed by the absorber 5a and do not give any influences to radio waves radiated to the upper side, because the high frequency side of the frequency band of this antenna is radiated from the central part of an antenna base 1. Moreover, radio waves of intermediate frequency bands are radiated from the intermediate ring-shaped section on the base 1 and, therefore, radio waves radiated to the lower side are absorbed by the absorber 5b and do not give any influences to the radio waves radiated to the upper side. The same thing happens in the case of radio waves on the low frequency side. Since radio waves radiated to the lower side can be absorbed by means of wave absorbers having the highest absorption characteristics against radio waves of various frequencies, radio waves can be radiated under the optimum condition.
MIZUTAME HITOSHI
AKAISHI AKIRA
MITSUBISHI ELECTRIC CORP
| JPS5352339A | 1978-05-12 |