Size Optimized Antenna-in-Package with Quasi-Isotropic Radiation Pattern

The Internet of Things applications require small wireless sensors with quasi-isotropic radiation, so that their communication is orientation insensitive. A method to realize quasi-isotropic antenna is by placing multiple radiators on the faces of a cube, which also acts as a package for the embedded electronics. In this work, we demonstrate quasi-isotropic radiation through a 3D Antenna-in-Package with multiple magnetic Hertzian dipole radiators. For quasi-isotropy, the dipoles on four faces of the cube must be in phase, while the dipoles orthogonal to the plane carrying the other four dipoles must be 60° out of phase. With this feeding arrangement, an isotropy of 7.3 dB has been achieved in the whole radiation sphere in simulations and 6.5 dB in a prototype where the ideal dipoles were replaced by practical microstrip patch antennas. The inner walls of the cube have been metallized to provide effective shielding between the antennas and the embedded electronics. We also optimized the size of the cube while maintaining a decent isolation between the adjacent patches so that the required quasi-isotropic radiation can be achieved. It is observed that the isotropy increases by reducing the size of the cube until the coupling between the multiple radiators starts to negatively affect it. As a trade-off between size, acceptable coupling and decent isotropy, a cube with
$\frac{\lambda_{o}}{2}$
sides has been designed, prototyped and tested.