Dīvide et īmpera? Multi-Functional RF Filtering Components for Modern Wide-Band/Multi-Band Wireless RF Front-Ends

Due to the necessity of lower-size/volume and optimized RF front ends for emerging wireless systems, the development of RF multi-functional components is acquiring a great interest. This means RF devices capable of carrying out multiple RF-processing actions in the same circuit. When compared to the classic RF chains based on the in-series cascade of independent monofunctional blocks (i.e., “Dīvide et īmpera” approach), benefits of the multi-functional philosophy are: (i) higher physical compactness, (ii) insertion-loss reduction due to the avoidance of interconnecting RF interfaces between blocks, and (iii) enhanced performance with the multifunction co-design. Within this trend, special effort is being made to integrate the filtering functionality in other types of RF circuits, such as power dividers, amplifiers, or baluns. Thus, new families of multi-operation filtering devices are being conceived. The aim of this tutorial is to introduce main approaches to design multi-functional RF filtering circuits as an emerging research topic in the field of RF electronics. This includes the description of different types of multi-functional RF filtering components with static and adaptive behavior for ultra-wideband and multi-band applications. Their theoretical foundations and illustrative design examples are described. Besides, several experimental prototypes in different technologies and frequency bands are shown. Moreover, system-level implications derived from the use of multi-functional RF components in complete RF front-end chains are also discussed.