Wearable electronics must be easily integrated into clothing while providing a highly reliable communications link. These requirements have raised the demand for miniaturization of on-body electronic systems. Multiple antennas, for example, can be replaced by a single, broadband radiator. The electronics in support of this antenna can, in turn, be centralized and reduced in size. At Belgium’s Ghent University, Arnaut Dierck, Hendrik Rogier, and Frederick Declercq have experimented with integrating Global Positioning System (GPS) and Iridium satellite-phone antenna capabilities into one active antenna.
This wearable, multiband, circularly polarized active antenna was created using flexible foam and fabric substrates together with conductors etched on thin copper-on-polyimide films. The feed substrate integrates a low-noise-amplifier (LNA) chip directly underneath the antenna patch. That active portion enhances signal reception by amplifying the incoming signal.
Antennas had previously been presented with sufficient bandwidth to cover both the GPS L1 and Iridium bands. However, the techniques used to realize circular polarization led to such polarization covering a small frequency range, which cannot cover both GPS and Iridium bands. By using a hybrid coupler, the researchers sought to increase the bandwidth in which the antenna is circularly polarized. They succeeded in attaining bandwidth of 183 MHz in which the antenna is circularly polarized with an axial ratio (AR) below 3 dB. The extra bandwidth provided by the hybrid coupler also provides robustness against fabrication tolerances.
To eliminate probes through the antenna substrate and raise robustness and flexibility, the researchers chose an aperture-fed topology. Both active and passive antennas were prototyped. The team studied antenna performance under bending conditions and in the presence of a human body. The active antenna realized gain beyond 25 dBi across a 1-dB gain bandwidth of 119 MHz. See “A Wearable Active Antenna for Global Positioning System and Satellite Phone,” IEEE Transactions On Antennas And Propagation, Feb. 2013, p. 532.
