title: Two-stage radio-frequency interferometer sensors.
abstract: We show that simple radio-frequency (RF) interferometers can have slow-wave positive group delay (PGD) or negative group delay (NGD), as well as superluminal propagation (SP) regions, due to a destructive interference process. These properties are easily tunable, which makes RF interferometers unique among systems that have NGD and SP regimes. A two-stage interferometer arrangement, which includes a first stage interferometer in the material-under-test path of a second stage, has significantly improved sensitivity in comparison with a one-stage reference interferometer. With a power divider based first stage and at its maximum NGD frequency, the frequency sensitivity improvement is as high as 7 times. With a quadrature based first stage, the sensitivity is increased by as much as 20 times. Sensitivity improvements are also observed at PGD and SP frequency regions.
authors.affiliation: Department of Electrical and Computer Engineering, Clemson University , South Carolina 29634, USA.
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Osterberg
authors.affiliation: Department of Electrical and Computer Engineering, Clemson University , South Carolina 29634, USA.
authors.forename: Pingshan
authors.initials: P
authors.lastname: Wang