Development of Measurement Methods in Microwave and Terahertz Ranges of Electromagnetic Waves in Ukraine (Review)

The review analyzes Ukrainian scientists’ achievements in measurements in the microwave and terahertz ranges of electromagnetic waves. The application of ultrashort ultrawideband pulses for subsurface probing and object detection is considered. Such instrumentation tools have practical application in the long-wave part of the microwave range. In the centimeter and millimeter ranges, the method of synthesizing time signals based on multifrequency measurements is promising, and a pulse duration of 70 ps was achieved. The performed synthesis is based on the principle of the Fourier holography in the frequency-time domain, and methods of the parametric spectral analysis are used to obtain signals in the time domain. Some devices are based on the Michelson interferometer idea, which is implemented in a cross of oversized waveguides, the E-plane waveguide cross. Multiprobe meters made it possible to obtain values of the complex reflection coefficient. Such a meter implements the principle of holography on counter-propagating beams in a discrete version. Based on this approach, non-contact vibration meters have been practically implemented. Neural networks found applications for the calibration of detectors and the recognition and estimation of coordinates of objects. Resonance measurement methods are represented by various resonators, such as resonators with “whispering gallery” oscillations, combined open resonators with a short-circuited waveguide section, and coupled biconical resonators. Methods for the physical characterization of liquids in ultra-small volumes of the order of a microliter have been implemented. Such measurements are based on determining the resonant frequency and the quality factor of the mode of oscillations, the determination of which, generally, involves the need to use the fractional rational approximation. Resonance sensors have improved the means of near-field scanning microscopy. Measurements of material properties and nondestructive testing are based mainly on solving the appropriate inverse problem for layered structures. This review presents the research results in this field.