Foldable All‐Textile Cavity‐Backed Slot Antennas for Personal UWB Localization

Abstract

An all‐textile multimoded cavity‐backed slot antenna has been designed and fabricated for body‐worn impulse radio ultra‐wideband (IR‐UWB) operation in the 3,744–4,742.4 MHz frequency band, thereby covering Channels 2 and 3 of the IEEE 802.15.4a standard. Its light weight, mechanical flexibility, and small footprint of 35 mm × 56 mm facilitate integration into textile for radio communication equipment for first aid responders, personal locator beacons, and equipment for localization and medical monitoring of children or the elderly. The antenna features a stable radiation pattern and reflection coefficient in diverse operating conditions such as in free space, when subject to diverse bending radii and when deployed on the torso or upper right arm of a test person. The high isolation toward the wearer's body originates from the antenna's hemispherical radiation pattern with a −3 dB beamwidth of 120∘ and a front‐to‐back ratio higher than 11 dB over the entire band. Moreover, the antenna exhibits a measured maximum gain higher than 6.3 dBi and a radiation efficiency over 75%. In addition, orientation‐specific pulse distortion introduced by the antenna element is analyzed by means of the System Fidelity Factor (SFF). The SFF of the communication link between two instances of this antenna is higher than 94% for all directions within the antenna's −3 dB beamwidth. This easily wearable and deployable antenna is suitable to support IR‐UWB localization with an accuracy in the order of 5 cm.

Fully Flexible Textile Antenna-Backed Sensor Node for Body-Worn UWB Localization

“…The results from [ 24 , 25 , 26 ] prove that the cavity-backed slot antenna topology is suitable for the goals stated in Section 2.1 . The antenna topology allows for low pulse distortion, and its distance estimation errors induced by a phase-center shift are in the order of 5 cm in all directions when considering a body-worn scenario [ 26 ], causing it to qualify for the 10 cm criterion. Furthermore, the frequency-domain characteristics of the topology remain stable when such an antenna is subject to bending or when placed in proximity of a human body [ 24 ].…”

“…The antenna is based on the coupled half-mode cavity-backed slot antenna design in [ 26 ]. In this topology, the open ends of two differently dimensioned SIW half-mode cavities are placed in close proximity.…”

“…Through thorough computer-aided design, a suitable choice for the half-mode cavity dimensions and their mutual spacing is found, causing the coupled half-mode cavities to cover the entire desired frequency range. A minor redesign is performed on the antenna from [ 26 ], since the integration of the electronics required a comparatively smaller pin diameter. The resulting antenna dimensions are specified in the caption of Figure 2 .…”

“…The results from [ 24 , 25 , 26 ] show that the antenna topology exhibits a directive radiation pattern oriented away from the human body, with a measured front-to-back ratio (FTBR) higher than 11 dB within the IEEE 802.15.4-2011 Channels 2 and 3. These results also demonstrate that this antenna topology exhibits low coupling with the human body, thereby reducing the wearer’s Specific Absorption Rate (SAR) and limiting the influence of human body proximity on the radiation pattern and impedance matching of the antenna.…”

“…The resulting antenna exhibits a reflection coefficient with respect to 50 lower than −10 dB over both Channels 2 and 3 of the IEEE 802.15.4-2011 standard (3744 MHz–4243.2 MHz and 4243.2 MHz–4742.4 MHz, respectively). Furthermore, the results from [ 26 ] indicate that the selected antenna topology is a suitable choice to reduce the phase center shift as a function of incident angle as much as possible, as is required for accurate localization applications. Moreover, [ 26 ] proves the feasibility of this antenna topology for on-body deployment, as both its reflection coefficient with respect to 50 and its radiation pattern remain stable under diverse deployment circumstances, such as in free space with and without mechanical bending or when worn on the torso or on the upper right arm of a test person.…”