A Uniplanar Dual-Band Quasi-Isotropic Antenna Using 1.5-Wavelength Folded Dipoles

In this letter, a novel uniplanar dual-band quasi-isotropic antenna is proposed. It consists of two folded dipoles, each with a length of 1.5 wavelengths, operating at their respective frequencies. The two arms of each dipole are folded twice, resulting in three pairs of branches. Specifically, two of these pairs function as the out-of-phase current sources and orthogonal current sources, respectively, collectively contributing to a quasi-isotropic radiation pattern. The third pair serves as the pair of feeding parallel transmission lines. By placing the two folded dipoles together, dual-frequency performance is achieved. Both folded dipoles share the same feeding parallel transmission lines, promoting a compact design. Antenna measurements show a uniform radiation pattern, with a maximum gain variation of 3.2 dB at 0.9 GHz and 6.5 dB at 1.8 GHz.