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A new application of a rectangular waveguide structure with a choke from Baskakova and Hoffmann (2021) is proposed for high-contrast imaging in the W-band. As with homogeneous lossy waveguides, the field distribution in front of the open-ended sensor is observed and a calibration/correction method is applied. The sensor is evaluated using planar metal- dielectric samples under test (SUT), thus enabling the detection of different materials with a standoff distance ranging from 0.08 to $1.07~\lambda _{0}$. The sensor can determine both amplitudes and the contrast of the reflection coefficients correctly at the reference plane of the SUT, which is not possible for state-of-the-art sensors. The maximum contrast of the imaging is greater than 26 dB. A spatial resolution and minimum resolution for the tracking of SUT local properties of 1.9 mm are achieved at standoff distances of 2 and 1 mm, respectively. [ABSTRACT FROM AUTHOR]

Novel sensors for ultrashort-distance measurements, with choke flanges applied at the open ends of both a WR10 waveguide and a circular waveguide, featuring a radius of 1.42 mm, are proposed. Field distributions between the sensors and a target are analyzed and explained on the basis of higher order modes of a radial line formed by the sensors and a planar reflective target. A robust equivalent circuit using a cascade of lossy waveguides is proposed and a new calibration/correction method is derived. Properties of both sensors are verified experimentally for target distances of 0–6 mm (more than one and half of wavelength). The new circular waveguide sensor operates in a frequency band of 75-76 GHz with a maximum error of measured distance $19~\mu \text{m}$. The new rectangular waveguide sensor enables to use an outstanding applicable frequency bandwidth from 76 up to 86 GHz, with best properties around 80 GHz, where the maximum error of the measured distance is 12 $\mu \text{m}$. The new sensors make possible to achieve about ten times smaller distance measurement errors in comparison with the state-of-the-art sensors. [ABSTRACT FROM AUTHOR]

new four-port component, dual-mode impedance transformer for wideband matching of two microstrip lines with equal characteristic impedance and a coupled microstrip line with general even- and odd-mode impedances, is proposed. Practical realization problems are discussed and a new dimension correction approach is derived. Two transformers between 50- $\Omega $ microstrips and microstrip coupled lines with even/odd impedances $100~\Omega /68~\Omega $ and $36~\Omega /27~\Omega $ , respectively, were built. The concept was experimentally verified at the frequency band 0.01–16 GHz. [ABSTRACT FROM AUTHOR]