Textile antennas directivity

For textile antennas without a ground plane, the presence of the human body produces substantial effects on the antenna performance because it acts as an absorber for the radiated field and represents an additional loading. This mainly alters the antenna input impedance and efficiency. Radiation patterns also change with respect to the free-space situation the human body acts as a lossy reflector, making the radiation pattern more directional in the off-body direction. An example of such a behavior, on a wearable antenna without ground plane, is shown in Fig. 26.5, where the on-body and free-space horizontal pattern of a wearable UWB monopole antenna on a polyi-mide substrate (realized by the EM group of Ghent University), are compared. 

Textile antennae can be incorporated into clothing systems for long-distance communication (Salonen and Rahmat-Samii, 2006). They can be directly printed onto a textile substrate or a micro-patch anteima attached to a vest. Depending on the environment, such antennae can operate in the range of 10-100 m. Longer-distance communication can be achieved by improved technology and the use of laptop computers or mobile phones. Very short distance connections can be made by wireless links using induction. Data can also be transferred by Bluetooth modules if the soldiers are located close to a central control facility. 

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