A High-Directivity, Wideband, Efficient, Electrically Small Antenna System

A high-directivity, wideband, efficient, near-field resonant parasitic, electrically small antenna system is presented. By introducing two different near-field resonant parasitic (NFRP) Egyptian axe dipole elements oriented in parallel in the near field of a traditional small dipole antenna, two nearby fundamental resonance modes are produced. Both are much lower in frequency than the fundamental mode of the driven dipole. The corresponding frequency bands of both resonators are optimized to be overlapping in order to create a wide operating bandwidth. The resulting antenna has linear polarization radiation characteristics broadside to the stack of planes containing the radiating elements. The currents on the NFRP elements dominate the radiation process and are designed to be out-of-phase to achieve a high directivity endfire effect perpendicular to the element stack. A prototype of the antenna is fabricated and tested to demonstrate the effectiveness of this design. The measured results show that this low-profile ( total height = 0.092 λL, where λL indicates the free-space wavelength corresponding to the lower bound of the operating frequency band) and electrically small ( ka = 0.679) antenna provides broadside realized gains in the range of 2.62 ±0.99 dB with ~ 10% fractional bandwidth. The performance characteristics of a yet smaller version ( ka = 0.494) are also explored numerically.