Broadband, efficient, electrically small metamaterial-inspired antennas facilitated by active near-field resonant parasitic elements

The possibility of using an active internal matching element in several types of metamaterial-inspired, electrically small antennas (ESAs) to overcome their inherent narrow bandwidths is demonstrated. Beginning with the Z antenna, which is frequency tunable through its internal lumped element inductor, a circuit model is developed to determine an internal matching network, i.e., a frequency dependent inductor, which leads to the desired enhanced bandwidth performance. An analytical relation between the resonant frequency and the inductor value is determined via curve fitting of the associated HFSS simulation results. With this inductance-frequency relation defining the inductor values, a broad bandwidth, electrically small Z antenna is established. This internal matching network paradigm is then confirmed by applying it to the electrically small stub and canopy antennas. An electrically small canopy antenna with ka=0.0467 that has over a 10% bandwidth is finally demonstrated. The potential implementation of the required frequency dependent inductor is also explored with a well-defined active negative impedance converter circuit that reproduces the requisite inductance-frequency relations.