This paper presents the recent research of the COMbat

The Mobile User Objective System (IMUOS) is the Navy's next generation narrowband tactical communications system that will provide a significant increase in capacity and link availability to disadvantaged users, including handheld terminals. Future MUOS antennas will have a receive band of 243 MHz -270 MHz and a transmit band of 292 MHz -31 7 MHz with a voltage standing wave ratio (VSWR) of less than three across both bands. Additionally, the antenna should be circularly polarized with a nearly omni-directional radiation pattern above I O degrees in elevation for optimum satellite coverage. A helmet-mounted antenna that can meet the space and weight constraints imposed b, v the application is a twoturn spiral with a different pitch to each turn. Our design is a two-arm Archimedes spiral encapsulated in a nylon shell that fits over the standard-issue US Kevlar helmet.The antenna was modeled and simulated using Ansoft's High Frequency Structure Sinzulator (HFSS) software. A half-power beamwidth of I20 degrees, a front-to-back (zenith-to-nadir) ratio of 3.6 dB, and a VSWR of less than three were achieved using a feed port impedance of I50 ohms. Recent work includes spec@ absorption rate (SAR) calculations and the addition of a reflector ring, which increases the front-to-back ratio and reduces the feedport impedance to the standard 50 ohms.

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