| 摘要 |
PURPOSE:To obtain a spiral antenna which is hardly affected by a higher order mode and reflecting waves from the bottom, has a wide band directivity, and is light in weight, by constituting a conductive cavity by using a CFRP. CONSTITUTION:A conductive cavity 3 is constitute by using a CFRP. When the cavity 3 is constituted in such a way, radio waves are radiated to both upper and lower sides of an antenna base 1 by a high-frequency electric current flowing to a spiral arm 2 through a connector 6 and balun 4, but the radio waves radiated to the lower side reach the base of the CFRP cavity 3 after they are damped by a wave absorber 5. However influences of the radio waves reaching the base of the cavity 3 to the radio waves radiated to the upper side become less, because the conductivity of the CFRP is lower than that of a metal by several figures. In addition, the degree of the influence to the radiation pattern also becomes less, since a higher order mode produced due to the existence of the side face of the cavity is also damped on account of the low conductivity of the CFRP. Furthermore, because of the CFRP being about a half of aluminum in specific gravity and equivalent to the aluminum in strength, the antenna can be reduced in weight. |
