Two-element Egyptian axe dipole arrays emphasising their wideband and end-fire radiation performance

Combinations of two metamaterial-inspired electrically small antennas are investigated numerically to achieve high directivity and enhanced bandwidth operation near 300 MHz. Two Egyptian axe dipole (EAD) antennas, one active and one passive, are arranged in an end-fire array configuration. The elements are designed to optimise the out-of-phase current distribution of the parasitic element to achieve enhanced directivity performance characteristics, including a peak gain >4.5 dB, front-to-back ratio >15 dB, and radiation efficiency >74% over a 3.73 MHz frequency range centred at 312.9 MHz when the separation distance between the elements is ~0.04λ_res and the total electrical size of the array is ka = 0.43. By simply increasing the width of both EAD parasitic elements, the array´s end-fire characteristics are transformed into a configuration that has more than a six times increase of the impedance bandwidth. A frequency-agile version of the array is obtained by incorporating a varactor between the two EAD parasitic elements. The simulation studies indicate that this frequency-agile, electrically small, end-fire array provides a much wider effective impedance bandwidth with improved end-fire radiation characteristics.