This paper presents a novel design method for reducing the complexity of the design procedure for diversity antennas on the hand-held phone. Recently, antenna selection diversity has been widely used for hand-held phones in order to overcome a problem of fading. A monopole antenna and an inverted-F antenna are the typical combination for this purpose. In the case of the conventional design method, the mutual coupling between two antennas are used for improving the diversity performance. However, strong mutual coupling often makes the diversity antenna design difficult and degrades the radiation performance. The proposed design method suppresses this coupling by tuning the terminating impedance on the unselected antenna and improves the diversity performance by modifying the shape of inverted-F antenna. The validity of the proposed method is investigated under the effect of the user's hand and head by FDTD simulation.

Recently, antenna selection diversity has been widely used for hand-held phones to overcome a fading problem. A monopole antenna (MPA) and an inverted-F antenna (IFA) are the typical antennas used for this purpose. However, strong mutual coupling generally appears between these two antennas and often makes the diversity antenna design difficult. In particular, in the case that the MPA is unselected antenna the mutual coupling can be minimized using the open terminating impedance. On the other hand, in the case that the IFA is unselected antenna the terminating impedance, which can minimize the mutual coupling, has not been clarified. This paper presents a novel analytical method for optimizing the terminating impedance of the IFA. The method exploits the Z-matrix, and the final expression of the terminating impedance is expressed by self- and mutual-impedance. The numerical and experimental results confirm that the proposed optimization method is effective for minimizing the mutual coupling.