Theoretical analysis and some experiments on Vierergruppe Antenne (Two-dipole antennas)

A center-fed full-wave dipole antenna located one-quarter wavelength above a reflecting plate has a very low potential relative to the plate, at the center of each half-wave element. When metal support bars are attached between these center points and the reflector plate to support the antenna, the structure is called a "metal supported full-wave dipole antenna." An antenna made up of two such full-wave dipole antennas has four half-wavelength antenna elements and has been named "Vierergruppe Antenne." This antenna and the "Achterergruppe Antenne" were invented in Germany. Vierergruppe antenne (sometimes called two-dipole antennas) can be rugged because they are made entirely of metal and do not require insulator supports. They also have excellent electrical characteristics over a very wide frequency range, and are widely used by TV and FM broadcasting stations around the world. Since the full-wave dipole antenna element is composed of a conductor having a diameter as large as 1/20 of the operating wavelength, it is unsuitable to use conventional thin conductor theory to analyze the antenna behavior. In particular, the current at the end of the thick solid antenna element will not be zero, as in the case of the thin one. Flat end-face currents are determined by using a quasi-static approximation and the moment method of analysis. Accordingly the excellent characteristics of this antenna have been found theoretically and fully clarified in the quarter century since its invention.