Get Rid of RF Isolators! Advanced Reflectionless Microwave Filtering Components for Emerging Compact/Energy-Efficient Wireless RF Front-Ends

RF isolators are usually employed in RF front-ends chains to prevent active stages to be damaged by the presence of RF signal-power reflections created by the passive stages (e.g., pre-select RF bandpass filters) in their out-of-band regions. Indeed, such RF signal-power reflections may induce RF amplifiers to operate in non-linear regime or to create additional undesired mixing products in frequency-conversion stages, which may result in the malfunctioning of the entire RF transceiver. Whereas passive and active RF isolators avoid this problem, this is done at the expense of higher size/volume and increased DC power consumption, respectively, as well as higher cost. A more-efficient solution that is recently gaining a considerable research attention may be the exploitation of “reflectionless” RF passive filtering devices, where the out-of-band signal energy is dissipated inside the circuit instead of being reflected back to the source so that RF isolators are no longer needed. The purpose of this talk is to familiarizing the audience with the emerging topic of reflectionless/ absorptive RF passive filtering components, which may result in considerably benefits for emerging RF front-end chains of new wireless systems (e.g., 5G and beyond) in terms of energy-efficiency/DC-power-saving, overall size/volume, and cost. After introducing the problematic of RF power reflections in RF front-end chains and classic solutions to circumvent them with their limitations, main strategies for the design of reflectionless RF passive filtering components as new paradigm are described. Experimental results of several proof-of-concept demonstrators in a variety of RF technologies will be also presented.