Fig. 1: Overview of challenges and proposed solution.
From: Passive frequency comb generation at radiofrequency for ranging applications
a Miniaturized RF passive tags radiate their backscattered signals omnidirectionally. Consequently, their readers are prone to loss of accuracy due to multipath interference, especially when operating in rich-multipath settings. b The receiver of RF transceivers may experience loss of accuracy due to clutter when remotely sensing a parameter of interest through a linear RF passive tag. TX: transmit, and RX: receive. c RF transceivers using the same frequency channel for both transmission and reception may suffer from loss of accuracy due to self-interference (SI) when sensing a parameter of interest through a linear passive tag; SI may be caused by limited isolation in the circulator that such transceivers generally leverage to be able to transmit and receive information with the same antenna. d–f Schematic representation describing the spectral characteristics of interrogation and backscattered signals for linear RF passive tags, harmonic tags and quasi-harmonic tags (qHTs). g Dependance of qHTs’ comb line spacing \(\varDelta f\) on their received power level \({P}_{r}\). h Dependence of \({P}_{r}\) on the distance \(d\) of a qHT. i Flowchart illustrating the required steps to read-out \(d\) from \(\varDelta f\). j A typical application scenario for qHTs, wherein the position of a qHT onboard of a drone is resolved by extracting the \(\varDelta f\) values produced by the qHT after interrogating it sequentially with three separate beacons located at three known positions. The extraction of the drone distance from each beacon allows the localization of the drone with high accuracy, even in GPS-denied settings.
