Simple Front-End Concept for the Complex Challenges of Multi-Band Communications

This paper proposes a new architecture for mobile phone front-ends that dramatically reduces the complexity of multi-band smart phones. Traditional smart phone front-ends consist of many parallel transmit (Tx) and receive (Rx) chains each dedicated to a single band. The proposed architecture simplifies this by making few fully frequency tunable Tx and Rx chains that each cover multiple bands. Three implementations of antenna systems for the proposed architecture are shown and discussed. They all consist of separate Rx and Tx antennas with more than 25 dB of isolation in between. Combined with additional tunable Rx and Tx filters the Rx/Tx isolation reaches 50 dB which is comparable with the isolation achieved with commercially available static duplex filters. Based on these antenna designs it is concluded that the proposed architecture is feasible for LTE phones and makes full coverage of all LTE bands realistic. Current 5G investigations show that the advantages of flexible front-ends will be even bigger as technology moves toward software defined radio.