High directive compact antenna with non-foster elements

Performance characteristics of passive electrically small antennas are limited by fundamental physics. Using active elements into antenna structures appears like an opportunity to overshoot those limits. Non-Foster elements are classically used in matching networks for electrically small antennas in order to increase their impedance matching bandwidth. In this paper, Non-Foster elements are proposed as innovative method to achieve a broadband high directive compact antenna at 868 MHz. The analysis is computed considering a three-element compact parasitic array. The impedance loads associated to each parasitic element have been calculated using an optimization procedure based on spherical wave expansion. Finally, the concept has been validated by electromagnetic simulations.