A Low‐Profile Unidirectional Antenna That Uses Folded Dipole With High Input Impedance as the Radiator

ABSTRACT By studying the impedance characteristics of the horizontal half‐wave dipole near the metal reflector, we find that the antenna input impedance decreases when the distance between the dipole and the reflector is reduced. Therefore, a folded dipole with high input impedance is considered to replace the half‐wave dipole to reduce the antenna profile. The folded dipole developed here occupies two connected dipoles with different widths, which is conducive to obtaining a higher input resistance, in other words, to obtaining a lower profile. In the rectangular area enclosed by the folded dipole, a coupling branch is added to extend the bandwidth. The antenna can cover the 2.3–2.62 GHz band, and provide stable directional radiation. Its size is only 0.35 × 0.2 × 0.08λ 3 ( λ is the free space wavelength corresponding to the center frequency of the dipole operating band). We made a prototype of the antenna and tested it. Both the measured and simulated results verify the effectiveness of the method of using such a dipole with high input impedance to reduce the antenna profile. The proposed antenna can be used in base station system.