Ultra-wideband conformal helmet antenna

Abstract

This paper presents the development of an ultra-wideband (300 to 3000 MHz), vertically polarized, nearly omni-directional (in azimuth) communications antenna integrated into the camouflage cover of a standard military-issue Kevlar helmet. The Helmet Camouflage Cover Antenna (referred to as the "helmet antenna") is one of three antennas (with the combined frequency coverage from 2 to 2000 MHz) based on the antenna COMbat Wear INtegration (COMWIN) concept developed at the Naval Postgraduate School (NPS) for the man-portable implementation of the new Joint Tactical Radio System (JTRS). The results of computer simulations and prototype measurements for the helmet antenna are presented. The helmet antenna is conformal to the shape of the Kevlar ballistic helmet. It is constructed of conducting cloth (polyester interwoven with nickel/copper fibers) and attached as a liner to the helmet's camouflage cover. The helmet antenna is therefore visually undetectable, except for the connector in the back of the helmet. Several variants of the helmet antenna have been designed and simulated at NPS using the High Frequency Structure Simulator (HFSS) software, with different trade-offs between the low frequency cut-off and the maximum VSWR "ripple" within the operational band. Two prototypes, Mk I and Mk II, have been built and measured at the NPS. Measurements of the input impedance/VSWR as a function of frequency for the Mk II prototype show performance exceeding the HFSS computer model predictions. The VSWR is less than 3:1 for all frequencies between 300 and 3000 MHz. The presence of an operator wearing the helmet does not affect the VSWR significantly.