This paper presents a broadband omnidirectional vertically polarized antenna of only a one eighth wavelength associated to the lowest frequency. This antenna is composed of a conical monopole with metallic parasitic elements, a capacitive disk and a dielectric substrate placed above a square ground plane. This structure provides broadband performances and omnidirectional radiation patterns over the whole bandwidth. Simulations and experiments demonstrate that this structure exhibits a 2.9:1 impedance bandwidth with VSWR below 2:1 and very good radiation patterns and gains in spite of a height extremely reduced.
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