Alternative duplexing for LTE FDD using the theory of characteristic modes

In this paper, we are investigating an alternative architecture for the RF transceiver of mobile phones which is capable of supporting the latest features and bands used for LTE. In this work, the duplex filter is replaced by equipping the Rx and Tx branch of the front-end with dedicated antennas. Duplexing is achieved by the less demanding tunable filters and the electromagnetic isolation between the two antennas. In order to satisfy the requirements of carrier aggregation (CA) and maintain the required antenna isolation, the theory of characteristic modes (TCM) has been used to obtain wideband antenna isolation. Both antennas are extremely compact in order to keep the overall antenna volume small. A wideband antenna has been used for the Rx whereas the Tx is equipped with a narrowband tunable antenna. This topology is dictated by the TCM analysis. The concept´s performance has been investigated through the measurements of prototypes. The results indicate that acceptable performance can achieved even for the more demanding tunable antenna.