A novel design of dual-band antennas with orthogonal radiation patterns for MIMO applications

Differential-mode dual-band antennas with frequency-selective scattering elements are demonstrated for MIMO applications. The input impedance of the small antenna is shown to be approximated with a cascade circuit of the antenna´s conductor and the coupling with the free space. With the results, differential-mode dual-band antennas were designed. Satisfactory return losses and omni-directional radiation patterns were obtained in both 2.5 GHz and 5.5 GHz bands. Using the antennas for both a radiator and a frequency-selective scattering element, pattern orthogonality is shown to be improved with both the simulated array factor and the measured radiation patterns. To obtain better orthogonality, frequency-selective scattering elements dedicated for each band in the shape of a line, an arc, and a parabola were estimated. A dual-band antenna with two scattering elements for the 2.5GHz and 5.5GHz bands exhibited excellent orthogonal patterns in both the bands.