A Compact Base Station Antenna Based on Ungrounded Radiator and Capacitive Compensation

In this letter, a novel miniaturization method for base station antennas based on ungrounded radiator and capacitive compensation is introduced. The miniaturization is achieved by loading a slot on the radiating structure of the dipole antenna to provide a capacitive component, thereby neutralizing the inductive component introduced by the ungrounded radiator. To broaden the bandwidth, a coupling layer, consisting of a printed square ring and a square patch, is introduced as a parasitic element above the antenna, inducing a new parasitic mode. In addition, the bandwidth is extended by enhancing the coupling between two pairs of dipole antennas through a downward extension of the radiator. The results reveal that the proposed compact antenna achieves a -10 dB bandwidth of 1.742.2 GHz (23.4%) with a radiator size of only 0.13 $\lambda_{L}^{2}$ and a profile of 0.209 $\lambda_{L}(\lambda_{L}$ is the wavelength at the lowest frequency).