A tunable RF Front-End with Narrowband Antennas for Mobile Devices

In the conventional full-duplex radio communication systems the Transmitter (Tx) is active at the same time as the Receiver (Rx). The isolation between the Tx and the Rx is ensured by duplex filters. However, increasing number of LTE
bands crave for multiband operation. Therefore, a new front-end architecture, addressing the increasing number of LTE bands as well as multiple standards, is presented. In such an architecture the Tx and Rx chains are separated throughout the front-end. Addition of bands is solved by making the antennas and filters tunable. Banks of duplex filters are replaced by tunable filters
and antennas, providing duplexer function over the air between the Tx and the Rx. A hardware system has been designed and fabricated to demonstrate the performance of this front-end architecture. Measurements demonstrate how the architecture addresses inter-modulation and receiver desensitization due to the Tx signal. The filters and antennas demonstrate tunability across multiple bands. System validation is detailed for LTE band I. Frequency response as well as linearity measurements of the complete Tx and Rx chains show that the system requirements are fulfilled.