Carrier aggregation and its challenges - or: The golden age for acoustic filters

With the advent of LTE-Carrier Aggregation (CA) as a means of increasing data rates in mobile device communication, a paradigm shift in the design of acoustic filters has been arising. Whereas before CA the focus of filtering has been on supporting one telecommunication band at a time, now multiple bands will have to be supported simultaneously over the same antenna. As a consequence, using switched filter banks is not an option anymore, and the only viable solution is to connect multiple Tx, Rx, and/or TDD filters to the same antenna pin. In this multiplexing configuration, several additional challenges need to be addressed when designing the individual filter components. The traditional requirements (low insertion loss, good out-of-band attenuation, tight impedance locus, good IMD behavior, power handling, and - in case of FDD bands - the highest possible Tx-Rx isolation) are no longer sufficient. Now designers also need to minimize loading of multiple filters by all the other filter's out-of-band impedance, optimize a multitude of cross-isolation requirements, and worry about a plethora of nonlinear mixing products (IMDx). This presentation provides an overview of these new challenges and discusses strategies to address some of them. Case studies will be reviewed and the next challenges lurking behind the horizon will be revealed.