A Low-Profile 1 × 2 Filtering Dipole Array With Small Unit Space and Closely Placed Ground

For the traditional 1 × 2 dipole array with a ground, the height should be about 0.25 wavelength, the distance between the dipole units needs to be 0.5 wavelength, and a traditional power divider is also required. The proposed 1 × 2 antenna array has an inserted stub-loaded resonator between dipoles and the closely placed ground. The signal can be coupled to the two dipoles through the resonator operating at odd mode. Therefore, the proposed 1 × 2 array exhibits low profile (0.1 wavelength) and a compact structure without power divider. Furthermore, the gain is a little higher than the traditional dipole array even though the distance between the dipole units is just 0.37 wavelength. In addition, the frequency selectivity can be enhanced by two radiation nulls near the band edge, which are caused by two even modes of the resonator. The bandwidth of the proposed array can be controlled by the couplings between the inserted resonator and the dipole array, while the radiation nulls can be controlled by the loaded stub of the resonator. A prototype is exemplified at 2.6 GHz with the measured 10 dB bandwidth of 8.8%, the gain of 8.2 dBi, and two radiation nulls at 2.1 and 4 GHz, respectively.