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We propose a flexible cluster array concept utilizing diverse antenna elements and the mutual coupling among them to improve the spherical coverage. This innovative approach can not only enhance the impedance matching but also improve the beamforming performance across a wide frequency band by adjusting excitation amplitudes and phases. Equations are derived to achieve specific objectives such as minimizing the total active reflection coefficient or maximizing the realized gain of an antenna array. To validate the concept, we employ a cluster array consisting of eight non-identical patch antenna elements with strong mutual coupling. When compared to a conventional four-element patch antenna array of the same size, the cluster array exhibits high beamforming capability over a wider frequency band. Simulated and measured results confirm that the operational frequency band can be extended from 24.5-26.5 GHz to 24.5-29.5 GHz, while maintaining a spherical coverage of over 6 dBi at the 50%-tile cumulative distribution function (CDF) of maximum realized gain.

In this paper, we present a dual-polarized frequencyreconfigurable patch antenna working at millimeter wave frequency bands for 5G applications. A square patch is surrounded by four metallic L-shaped walls. Four ideal varactor diodes are placed between the corners of the square patch and Lshaped walls. Frequency tunability is achieved by adjusting the capacitances of the varactor diodes. Two 50-Ω probes are used to feed the square patch which can excite two orthogonal polarizations. Operating frequency can vary from 23 GHz to 45 GHz with a 10-dB return loss when the capacitance decreases from 0.05 pF to 0.005 pF. The isolation between two polarizations is better than 13 dB over the operating frequency bands. Crosspolarization level is lower than −15 dB. In addition, the quality factor of varactor diodes is studied to demonstrate its influence on antenna efficiency.