Hertzian Magnetic Dipoles Model of a Quasi-isotropic radiation microstrip patch based Antenna-in-Package

The Internet of Things applications require small wireless sensors with quasi isotropic radiation, so that their placement is orientation insensitive. This paper shows the design steps for a microstrip patch based quasi-isotropic Antenna-in-Package (AiP). The structure proposed is a hollow cube with six microstrip patch radiators, one on each of its faces. The cubes internal walls are metallized to not only act as ground planes for the microstrip patch antennas, but also provide the necessary shielding between the radiators and the future embedded electronics. Thus, the problem in hand is to find the optimal phases to be applied to each patch so that when all six are activated simultaneously, the obtained radiation pattern is quasi-isotropic. Given the complexity of the structure, a simplified model of Hertzian magnetic dipoles was used to determine the phase each patch was to be excited to achieve the closest to an isotropic radiator as possible. A measured gain variation of 6.5 dB has been achieved for the entire 3D sphere after fabrication of a prototype.