Planar Electrically Small Folded Dipole Antenna

This paper presents a novel planar electrically small folded dipole antenna, which combines metamaterials theory with normal folded dipole's broadband, high-gain features. The whole structure simply incorporates a short folded dipole surrounded by two hat-shaped split semi rings. Due to the small dimension of short folded dipole, it cannot produce enough radiation resistance. Therefore, a pair of split rings serving as near-field resonant parasitic (NFRP) elements are proposed to increase the resistance and improve the impedance matching. Compared with smaller inside current in the driven elements, the parasitic elements function as the main radiation elements, forming a compact antenna array to improve the radiation. The simulated and experimental results that are in good agreement confirm the characteristic of electrically small antenna with only 0.17 lambda(0) x 0.43 lambda(0). total electrical size, 3 dBi directivity and about 50% radiation efficiency. Besides, this antenna is sensitive to the variation of environment, such as the thickness of surrounding materials. The proposed antenna owns characteristics such as electrically small, gain-enhanced, bandwidth-broadened, single layer, ultra-thin, sensitive to environment, which could be used for environment sensors or detecting applications.