Multiple Antenna Concept based on Characteristic Modes of Mobile Phone Chassis

All the concepts of multiple antenna for a small device are backed by the idea that the radiation properties are dominantly controlled by an antenna structure which is attached to the device. However, for typical handheld devices this assumption is no more valid. It is known that radiation from small devices is dominated by contributions from the chassis. This fact is used in our novel concept which considers the chassis as an antenna. Selective excitation of individual orthogonal characteristic mode currents on the chassis constitute the basis for a multiple antenna system. A feed network composed of 180deg hybrid couplers provide very good isolation between system ports. However, due to difference in mode impedances special measure must be taken to simultaneously match all the ports.