Broadband body-worn antenna using a top-loaded pyramidal radiator

A wide-bandwidth low-profile quasi-omnidirectional antenna is presented and experimentally demonstrated when integrated with a helmet for emergency services or military applications. The antenna consists of a pyramid-shaped radiator that is top-loaded with an etched copper-clad microwave laminate with two shorting strips used to improve the input impedance matching, particularly for lower frequencies. The design and operation of the antenna are first introduced using a flat ground plane, and then experimental results are reported when it is installed on a helmet where the outer surface of the helmet is used as the ground plane. The results show a very wide impedance bandwidth from 890 MHz to 13.7 GHz (VSWR $\le $<= 3) and predominately monopole-like radiation patterns up to $\sim $similar to 11 GHz. The antenna has a height of $\lambda $lambda/16 at the lowest operating frequency of 890 MHz (21 mm). Simulation results with a human body model demonstrate the significantly improved omnidirectionality of the proposed helmet antenna compared to more conventional body-worn antennas used in some applications.