Wave propagation in a double-layer below-cutoff lossy waveguide in the frequency range 5...30 ghz

Methods for determining complex permittivity of high loss liquids are essential in various branches of science and technology. In the microwave range it has been studied the propagation of electromagnetic waves in a circular double-layer metal waveguide with a central low-loss dielectric rod surrounded by a high-loss liquid. The dependencies of the complex wave propagation constant on frequency and the magnitude of the liquid layer were obtained. The presence of high-loss liquid surrounding the dielectric rod allows expanding the range of operating wavelengths from the millimeter to centimeter range. The value of the attenuation constant is relatively small. Due to a high loss medium, this waveguide structure does not have a fixed value of the cut-off frequency. An anomalously low value of the attenuation constant of the electromagnetic wave has been detected at the centimeter range for certain operating frequencies and liquid layers. The proposed structure can be applied as a measuring cell for the determination of the complex permittivity of high-loss liquids in small volumes.