Circularly-Polarized Antenna Design in Mobile Phones by the Combination of Common and Differential Modes

To meet the coming era of direct satellite-to-handset communication, this paper proposes two design cases of single- fed end-fire circularly-polarized (CP) antennas in mobile phones based on the combination of common mode (CM) and differential mode (DM). By employing a slot-etched planar inverted-F antenna (PIFA) or a slot-etched cavity antenna, a set of orthogonal-polarized modes, i.e., CM and DM, can be excited simultaneously by an asymmetrical feeding port. Then, by finely tuning the resonant frequency of the proposed orthogonal modes, a 90-degree phase shift between two modes can be realized, enabling a good CP performance in the end-fire direction. Simulation results show that a good left-hand CP directivity of 1.62 and 3.09 dBic can be realized for the CP PIFA and cavity antenna design cases, respectively. We predict that the proposed design can be a good candidate for the satellite communication antennas in mobile phones.