Design and characterization of purely textile patch antennas

In this paper, we present four purely textile patch antennas for Bluetooth applications in wearable computing using the frequency range around 2.4 GHz. The textile materials and the planar antenna shape provide a smooth integration into clothing while preserving the typical properties of textiles. The four antennas differ in the deployed materials and in the antenna polarization, but all of them feature a microstrip line as antenna feed. We have developed a manufacturing process that guarantees unaffected electrical behavior of the individual materials when composed to an antenna. Thus, the conductive textiles possess a sheet resistance of less than 1 Omega/square in order to keep losses at a minimum. The process also satisfies our requirements in terms of accuracy meeting the Bluetooth specifications. Our investigations not only characterize the performance of the antennas in planar shape, but also under defined bending conditions that resemble those of a worn garment. We show that the antennas can withstand clothing bends down to a radius of 37.5 mm without violating specifications.