Radioelectronics and Communications Systems

Development of measurement methods in microwave and terahertz ranges of electromagnetic waves in Ukraine (review)

Oleg Drobakhin — 2024-04-26

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.

Nonparametric method for joint estimation of broadband signal delay and its Doppler factor under influence of multiplicative interference

Pavlo Kostenko — 2024-04-26

The paper presents a nonparametric method for joint estimation of the delay time and Doppler factor of a pseudo-randomly phase-shift keying signal under a priori uncertainty about the probability distribution law of the white multiplicative interference in its observation. When estimating the signal parameters, the Doppler deformation of the envelope and shift of the carrier frequency are considered. The problem of estimating the signal delay time at a known Doppler factor is studied separately. The parameter estimation problem is investigated, assuming that the noise component is a process with independent and identically distributed random quantities (white noise).

The proposed method minimizes the goal function that uses observing BDS statistics. The delay time and the Doppler factor are determined by calculating the minimum value of the goal function of the mismatch between the observed signal and its model under conditions of joint variation of parameters. Properties of joint nonparametric estimates of the signal delay time and the Doppler factor obtained for different parameters of the BDS statistics have been investigated. There are presented dependences of mathematical expectations and mean square errors of joint estimates of the delay and Doppler factor of the received signal for several probability density distributions at different parameters of the multiplicative interference scale, including those with heavy tails. Using statistical simulation, it has been shown that the proposed method makes it possible to obtain acceptable estimates of signal parameters under a priori uncertainty about the distribution of multiplicative interference.

Inverse problem of triplet BPF with all mixed couplings

Sergii Litvintsev — 2024-04-26

In this article, using the inverse problem method, an analysis of a third-order bandpass filter (triplet BPF) with all mixed couplings was carried out. These filters have advantages over simpler triplet BPFs with partially used mixed couplings. The inverse problem method determines the mixed coupling coefficients of a triplet BPF from a given location of two transmission zeros (TZ) on the complex plane s = σ + jΩ. As a result of the analysis, it was found that triplet BPFs with all mixed couplings more effectively bring together TZs located on the σ or jΩ axis, which leads to an increase of flat group delay or BPF selectivity. Microstrip triplet BPFs with all mixed couplings use stepped-impedance resonators (SIR) located a short distance from each other. This results in very compact filters formed according to the “close-packed” principle. In such microstrip filters, increasing the thickness of the dielectric substrate makes it possible to increase the unloaded quality factor Q_u of the resonator and realize narrow passbands without increasing the area occupied by the filter. A universal microstrip triplet BPF with all mixed couplings is considered. It combines the properties of symmetric and asymmetric triplet BPF and provides 10 different locations of two TZs on the s-plane and forms significant variety of frequency responses.

THz-radiation sources on silicon avalanche transit time diodes

Andrii Bychok — 2024-04-26

The paper presents the results of research on the creation and development of radiation sources in the frequency range of 100–400 GHz using silicon (Si) avalanche diodes (ADs). Effective frequency converters of highly stable low-frequency signals with a level of 10–30 mW output microwave power of continuous radiation are proposed and implemented. The minimal circuit losses and maximum output power of ADs, which have a low impedance, are achieved in the oscillating system on an open radial line. The equivalent circuits of generators are considered and electrophysical parameters of avalanche structures are provided. Design schemes of radiation sources and their main parameters are also presented. The use of such radiation sources makes it possible to implement qualitatively new promising applications in this frequency range, in particular, to obtain high-resolution images of targets, to achieve transmission rates of up to 100 Gb/s and more, to study in detail properties of materials, and the structure of the universe.