To realize the ideal shape of a radiating pattern by arranging a shield plate obtained by laminating a radio wave absorbing layer on the upper surface of a metallic plate between a four-wire fractional turn helical antenna element and a control circuit to be connected to the lower part of the element, to support the lower part of the element by the upper surface of the shield plate.

A shield plate 74 consists of an aluminum substrate 85 and a radio absorber layer 86, such as a ferrite layer laminated on the upper surface of the substrate 85, e.g. The plate 74 is arranged between an antenna main body 75 and control circuits such as a hybrid circuit 76, a matching circuit to absorb radio radiated onto an airframe 71 or a base 72 in the neighborhood of an antenna from the antenna main body by the layer 86. Adverse effects which are given to he radiating characteristic of the antenna from reflected radio wave can be reduced. Electric field shielding effect between the main body and the control circuits is obtained by using an electrically conductive substrate 85, such as aluminum.