Special section on advanced tuneable/reconfigurable and multi-function RF/microwave filtering devices

Modern trends towards the design of highly-flexible next-generation multi-purpose RF transceivers for emerging applications, such as software-defined radio and radar systems, have reactivated the interest into reconfigurable high-frequency electronics. Microwave tuneable filters are among the most challenging components to carry out the adaptive frequency-band selection demanded by such systems; more still taking into account some critical factors to be considered in their development depending on the application; e.g., power-handling capability, non-linear/noise behavior, switching speed or quality (Q) factor over covered tuning range. On the other hand, a lot of attention has lately been detected in the development of RF/microwave multi-function circuits. This means sophisticated devices simultaneously showing multiple functionalities in the same electrical network. Benefits of this multi-function approach are compact size and more efficient implementations by means of the co-synthesis of different high-frequency components. Within this trend, a considerable effort has been dedicated to integrate the filtering function in other types of RF/microwave circuits, such as power dividers/combiners, antennas, amplifiers or baluns. As a consequence, completely new families of multi-operation filtering devices are being conceived.