A Low-Profile, Vertically Polarized Ultrawideband Antenna With Monopole-Like Radiation Characteristics

A compact, ultrawideband (UWB) antenna with an extremely low profile is presented. The antenna has consistent monopolelike radiation characteristics over approximately an 8.5:1 bandwidth. It consists of two radiators where one radiator is a smaller, slightly different version of the other one. The smaller radiator is partially embedded into the large one to avoid considerable increase in the maximum antenna height. Each radiator has two parallel loops in the shape of a bent diamond connected to the ground plane at their ends. A properly designed feed network is used to feed the larger antenna at lower frequencies while feeding the smaller one at higher frequencies to improve the consistency of the radiation characteristics of the system over a very broad bandwidth. A prototype of the proposed antenna and the feed network are fabricated and experimentally characterized. The fabricated antenna prototype has electrical dimensions of 0.26λ_min × 0.26λ_min × 0.046λ_min at its lowest frequency of operation and demonstrates monopole-like radiation characteristics with consistent, vertically polarized, omni-directional radiation patterns over roughly an 8.5:1 (0.66-5.6 GHz) bandwidth.