Radial-free collinear omni-directional triband half wavelength antenna with virtual ground, single coaxial cable feedpoint, and with minimal interaction of adjustment between bands

Abstract

An omni-directional triband antenna operates without ground radials with gain commensurate with a half wavelength vertical on each band. The triband antenna includes a dual-band twinlead J-pole providing half wavelength radiators for UHF and VHF, and an impedance transformer defining feedpoints to which a length Lc of coaxial cable is attached. The Lc lower end is the triband antenna connector port. Intermediate band radiators are first and second wire elements that collectively are a half-wavelength at the intermediate band. The first element is wound helically about the impedance transformer, with upper end floating and lower end connected to a first feedpoint. The second element is wound helically about the Lc upper portion of coaxial cable, with upper end connected to the remaining feedpoint, and lower end of the element floating. The helical windings radiate vertically and there is no cross-interference between antenna radiation in any of the three bands.