Two-Port-Quasi-Reflectionless Microwave Linear-Displacement Sensor Using a Balanced-Circuit Architecture

A microwave linear-displacement sensor with two-port-quasi-reflectionless behavior is proposed. It is made up of a balanced-circuit architecture comprising the following parts: (i) a reflective-type RF-sensing network—constructed by a pair of identical bi-path transversal-signal-interference (TSI) sections serving as the stator and a set of duplicated open-circuit-ended stubs built on a common slider—and (ii) two uniform wide-band 3-dB quadrature couplers—each composed of three-stage parallel coupled lines and a terminating resistor at the isolated node—at the input and output ports of the overall circuit. Thus, the frequency spacing between the notch bands of the RF-sensing network varies as a function of slider displacement. Meanwhile, the non-transmitted RF-signal energy coming from the RF sensing network is dissipated by the resistors of the couplers, achieving quasi-reflectionless characteristics at both ports. Finally, a 2-GHz prototype of the conceived RF sensor exhibiting a 20-mm dynamic range and an averaged sensitivity of 59.4 MHz/mm is manufactured and tested.