PURPOSE: To obtain an antenna in common use as two-frequency band possible for changing the angle of elevation and the azimuth angle, by performing beam wave guide feeding from an electromagnetic horn having mutually different frequency band via two concave reflecting mirrors and a frequency selecting reflecting plate.

CONSTITUTION: The beam wave guide feeding possible for changing the angle of elevation and the azimuth angle is performed from a main reflecting mirror 1, a subreflecting mirror 2 of a Cassegrain antenna section with reflecting mirrors 3, 4 of an angle of elevation turning section and reflecting mirrors 5, 6 of an azimuth angle turning section. A guide system for a beam wave through the concave reflecting mirrors 21, 22 and the frequency selecting reflecting mirror 23 is formed between a flat reflecting mirror 6 and the electromagnetic horns 24, 25 in a buidling 300 in which a transmitter/ receiver is installed. The transmission wave of a low frequency band is radiated from the horn 24 in this way, reflected on the reflecting plate 23 and led to the reflecting mirror 6 via the reflecting mirrors 22, 21. The transmission wave of a high frequency band is reflected on the horn 25, transmits the reflecting plate 23 and is led to the reflecting mirror 6 via the reflecting mirrors 22, 21. The two-frequency band is used in common in this way.