Beamwidth Reduction for Low-Profile Omnidirectional Antennas With an Annular Loading of Parasitic Elements

There is a dilemma for omnidirectional antennas between a narrow beam on the elevation plane and a low-profile antenna configuration. In this communication, an annular loading of parasitic elements mechanism is proposed to circumvent the difficulty. A study for the proposed analytical model shows that the radiation from the parasitic elements can sufficiently cancel the original one in unwanted directions and thus reduce the beamwidth sufficiently. This array-based mechanism is validated for an omnidirectional circular patch antenna. With a proper design of the coplanar parasitic elements, a beamwidth reduction of 50° for the maximum radiation toward the ground plane and 73° for the maximum radiation toward the direction of 45° above the ground plane has been achieved, respectively. Both antennas have a simple configuration, and the total antenna thicknesses are only 0.06 and 0.01 guide wavelength, respectively.