A novel design approach to high-gain, wideband, dual-resonant, closely-spaced, three-element Yagi-Uda antenna is advanced. The antenna is comprised by a full-wavelength, principal sectorial dipole, a circular metallic flat reflector, and a sectorial director. At first, a multi-source model is developed to predict the initial values of the key antenna parameters, e.g., the flared angle/radius of the director, and the separation between them. Then, as theoretically predicted, numerically simulated and experimentally validated, the flared angles of the principal radiator and the director are eventually determined as 270° and 180°, respectively. They are further tightly coupled at a close separation of 0.024-wavelength to yield relatively compact size and high gain simultaneously. Prototype antenna with a circular metallic reflector successfully exhibits an impedance bandwidth up to about 40%, with in-band maximum gain up to 10.4 dBi and gain fluctuation less than 3 dB. Finally, the antenna is comparatively studied with other Yagi-Uda antennas to highlight its unique wideband and high gain characteristics.