Helmet mounted UHF antenna for Mobile User Objective System (MUOS)

Abstract

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.

Wearable Antennas for Off-Body Radio Links at VHF and UHF Bands: Challenges, the state of the art, and future trends below 1 GHz

“…A helmet antenna experiences a little interference from the wearer's body and equipment as body, head and shoulders help to reduce back radiation toward nadir direction. In [79], human head and shoulders increase the F/B ratio by 3dB, but the half-power beamwidth decreases from 120 to 90 degrees. Also, the asymmetrical configuration (the spiral turn at the top of the helmet has a different pitch with respect to the lower spiral turn) helps to increase the F/B ratio (zenith-to-nadir ratio).…”

“…A circularly-polarized helmet antenna that covers the 243-317MHz band of the Mobile User Objective System (MUOS) for narrowband tactical satellite communications, has been designed and tested in [79]. The semi-conical asymmetrical antenna is a two-turn two-arm Archimedes spiral antenna.…”

“…At the UHF lower band, wearable antennas have been designed for personal and professional mobile radio systems operating around 400MHz [63]- [78] (as for example the TETRA [70] and TETRAPOL systems [73] [74]) and digital television (DTV) broadcasting reception (470-770 MHz) [81]- [88]. Helmet antennas for narrowband tactical satellite communications at around 300MHz [79] as well as antennas to be integrated into soldier/police armor vests [69]- [70] have also been designed. Wearable antennas for the user terminal of satellite-based search-and-rescue systems (Cospas-Sarsat system at 406MHz) have been proposed in [89]- [93].…”

“…The body effect is substantial for VHF antennas [62], since the wearer's body is entirely inside the antenna reactive near-field region. Also, some radiation absorption resonances are located exactly in the VHF band [55]: [70][71][72][73][74][75][76][77][78][79][80] MHz for whole-body SAR (Specific Absorption Rate), and around 300MHz for head SAR [10].…”

“…Several papers have been devoted to the analysis and design of VHF/UHF antennas integrated on helmets ( [60]- [61], [79]- [80], [104], [145]- [148], [155]- [156]), as any soldier, policeman, firefighter, as well as motorcycle riders and bikers, wear such a head protection. The main advantages of a helmet antenna are related to its "prime location", represented by the body head.…”