In this article, a novel design approach to wide beamwidth dual-resonant, wideband sectorial dipole antennas is advanced. At first, a 1-D, full-wavelength dipole is evolved into a 2-D, sectorial dipole, so as to determine its two usable resonant modes. Then, both wideband and wide beamwidth characteristics are simultaneously attained under dual-mode resonance. Next, dual-resonant sectorial dipole antennas with flared angle of 270° and 240° are designed and studied. As experimentally validated, the proposed antenna exhibits an omnidirectional pattern with its impedance bandwidth over 70.4%. A few prototypes mounted above a ground plane are further investigated, so as to achieve a broad H-plane half-power beamwidth (HPBW) to over 120°. In addition, the antennas exhibit stable gain frequency response with fluctuation less than 2.2 dB within the entire impedance bandwidth. Thus, the advanced design approach based on 2-D dual-resonant, full-wavelength dipole leads to the formulation of novel wide beamwidth antennas with low frequency dispersion and simple configuration within a wide radiation bandwidth over 53.3%. Finally, a dual-polarized dipole antenna with port-To-port isolation higher than 34.5 dB and available radiation bandwidth of over 49% is implemented to further validate its potential for practical applications.