Miniature Antenna for Circularly Polarized Quasi Isotropic Coverage

A novel miniature antenna with quasi-isotropic radiation pattern and optimized circular polarization is presented. This structure is well suited for small wireless devices whose orientation is arbitrary with respect to each other, especially for future applications such as wireless sensor networks. The miniature antenna (lambda/5 x lambda/5 x lambda/38) consists of 4 Inverted-F Antennas (IFA) arranged in a rotational symmetry and mounted on a small dual layer PCB. IFA elements are fed by a micro-strip network etched on the bottom layer. We obtain a total efficiency of more than 65% on a 100MHz bandwidth, a quasi-isotropic radiation pattern with an absolute maximum 3.6dB deviation relative to the ideal isotropic pattern and circular polarization in two large circular sectors pointing upward and downward with an average -3dB axial ratio beam width of 105deg. Finally, according to a previously published criterion, the isotropic coverage, radiation performances of this antenna are evaluated and compared to common antennas in the typical context of devices communicating together with arbitrary orientations with respect to each others.