Augmenting a Modified Egyptian Axe Dipole Antenna With Non-Foster Elements to Enlarge Its Directivity Bandwidth

Non-Foster elements are introduced to augment an Egyptian axe dipole (EAD) antenna-based system in order to expand its directivity bandwidth. The frequency-agile properties of the original antenna system are investigated near 300 MHz by linearly and discretely changing the values of its internal reactive element. The curve-fit reactance versus frequency curve is established. It is reproduced approximately by augmenting the antenna system with two non-Foster elements implemented internally in one of its near-field parasitic elements and with negative impedance convertor (NIC) designs. It is demonstrated that the resulting electrically small antenna system is capable of achieving excellent unidirectional radiation performance, including a broadside directivity in the range from 5.78 to 6.24 dB with more than a 20 dB front-to-back ratio (FTBR) over a 13% instantaneous fractional bandwidth. The corresponding half-power beamwidths in the E- and H-planes, respectively, are 78° and 138°; the radiation efficiency exceeds 65%.