4-WIRE HELICAL ANTENNA

摘要

The first embodiment is a 4-wire fractional-winding helical antenna in which a spiral conductor pattern is formed easily and precisely on the surface of a supporting member in the form of a cylindrical tube or a stepped cylindrical tube form by the photoetching technology. This 4-wire fractionalwinding helical antenna has an improved characteristics, in particular broader frequency bandwidth. Further, it can solve the problems with the winding of the helical conductors. The second embodiment is an antenna unit in which a shield plate is provided between the antenna and coupling and conversion circuits, the antenna-side face of the shield plate is coated with a material for absorbing electromagnetic waves, and the antenna plate comprises an aluminum or copper plate and a layer of ferrite on the antenna-side face of the aluminum or copper plate. This antenna unit can prevent the reflection by the components at the antenna base and the airframe of the electromagnetic wave from the antenna and hence deterioration of the directivity pattern.