Ultralow-Profile and Flush-Mounted Monopolar Antennas Integrated Into a Metallic Cavity

This letter presents an evolution of a low-profile monopolar antenna specifically designed for the integration onto large vehicles or house roofs. The use of a shallow cavity is investigated for a reduction of the antenna height seen from the ground plane. The tradeoff between the cavity size and effective height of the antenna is studied, where it is demonstrated that the sunken geometry is well suited for applications requiring omnidirectional patterns. Two antenna prototypes were developed: a low-profile one and a flush-mounted device both enclosed in a thin plastic radome. The experimental validation shows satisfactory antenna performance over a larger than 3:1 bandwidth with a monopolar pattern.