June 30, 2011

T-shirt Antenna

NPL (National Physical Laboratory) worked with BAE Systems Advanced Technology Centre, to measure the pattern and efficiency of radiation emitted from next generation wearable antennas embedded in T-shirts.

Wearable antennas could be the future of wireless technology and have important applications in communications, security and healthcare, but as they are worn on the body it is particularly important to understand their performance. The human body absorbs electromagnetic signals and so there are concerns that the emitted signal from the antenna could suffer from power losses if worn too close.

There is an optimum distance for the position of the antenna in relation to the body, which can improve the antenna's efficiency.

Explaining Antenna Gain

dB is a logarithmic unit and every 3 dB increase is a doubling of the power (intensity). This means that if you switch out your theoretic 0 dBi antenna for a 3 dBi antenna you will gain the same amount of extra range as doubling your transmitter output power. A 3 dB increment means an extended range by 1.414, a 6 dB increment means an extended range by 2 (1.414*1.414)

Here is a link to another site that explains antenna gain.

Existing Commercial wearable antenna system for about $600

The Tactical Vest Antenna System (TVAS) is a concealable antenna designed for military applications. The radiating elements slide smoothly over the SAPI plates inside the plate carrier, consequently placing the antenna out of enemy's sight, and out of the radio operator's way. The antenna system consists of two antenna inserts, two interconnecting cables, and a cable for radio connection. The TVAS also contains a quick release mechanism which allows the operator to disconnect the system in emergency situations. The system has 10 dBi gain which means about triple the range.

Optimal Frequency Range: 30 - 100Mhz
Total Frequency Range: 30 - 512Mhz
Gain: -10dBi at 30.00Mhz
Power Input: 7 Watts
Weight: 9oz / 255.14 grams
Coverage: Omni-directional
Interconnect Wire Length: 12"
Radio Compatibility: PRC-148, PRC-152, PRC-117, etc.
Radio Connector: TNC
Vest Type: Any with SAPI/ESAPI Pouches
Impedance: 50ohm

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