This article explores the design, modeling, and experimental validation of passive antenna arrays (AAs) tailored for unmanned aerial vehicle (UAV) communication systems. Focusing on the technical composition and functionalities of various types of passive antenna arrays, the study delves into different antenna elements that comprise these arrays, discussing their integration into comprehensive systems. Through rigorous modeling aimed at predicting performance in diverse operational conditions and backed by experimental studies, the paper provides practical insights for the development and optimization of AAs. These passive systems leverage the collective strength of multiple antennas to form directed beams, enhancing signal clarity and reducing interference, thereby supporting robust communication links essential for UAV operations. 

The article is devoted to the problems of constructing electromagnetic field with given parameters and both to the study of electromagnetic environment. For solving the problems, the corresponding theoretical material is presented. The functional relationships are considered that make it possible to construct the device for generating electromagnetic field with specified parameters in circular orthogonal polarization basis. The block diagram, which can ensure the specified field forming with acceptable errors are synthesized. Measurement of radiation characteristics, including polarization characteristics, requires the appropriate orientation of the receiving antenna to the direction of wave propagation. Corresponding algorithm and antenna system for this purpose is proposed. The study of the field polarization characteristics formed using the ring antenna elements is carried out. It is shown that in the broad frequency band, the ring elements can be replaced with spiral radiators, as well as that the antenna system for electromagnetic waves reception and their subsequent decomposition in circular polarization orthogonal basis, must contain at least eight antenna elements. Applied spiral flat antenna elements ensure the low level of cross-polarization due to the matched load on the spiral end, which is one of the conditions for successful polarization analysis. Besides, a device for polarization analysis of incident electromagnetic waves and the algorithm for measurement of the effective reflection area are considered.

The aviation security is an important component of aviation safety providing. One of the main goals of aviation security service is to detect dangerous and prohibited objects during passengers and baggage screening. For this purpose, aviation security personnel use various equipment: X-ray screening system, body-scans, metal detectors, moving ions detectors, explosive trace detectors. The X-ray screening system gives information on internal structure of baggage. The main disadvantage of X-ray screening system is rather high level of the false alarm probability. This requires developing new methods of image processing and recognition of dangerous and prohibited objects on the background of other objects. This article develops the principles of shadow image processing while screening the baggage using X-ray system to fix the mentioned disadvantage. The math equation for shadow image is obtained based on the laws of geometry and Beer-Lambert equation taking into account the chosen scanning technique. Based on this, the article is focused to the analysis of simple objects images and their application for complex objects recognition. The article discusses the example of handgun recognition using a new approach based on spectral analysis of developed shadow images. The results of the research can be used for improvement of algorithmic toolkit in aviation security automatic decision-making system while screening the baggage by X-ray equipment.

This article considers the peculiarities of using circular orthogonal polarization basis for measuring the parameters of an electromagnetic wave. In particular, the angle of inclination of the major axis of the polarization ellipse and the ellipticity coefficient are among measuring parameters. The main expressions for calculation of field parameters in circular and linear orthogonal polarization basis are developed and analyzed. The advantages of using the ring as a measuring antenna in comparison with symmetrical vibrators of the turnstile antenna are substantiated. The expressions obtained in the article for calculating the measurement errors of polarization parameters in a linear orthogonal polarization basis illustrate the multifactorial dependence of the measurement accuracy on the angular and amplitude parameters. In contrast to the linear polarization basis, in case of circular basis, the inclination angle of the polarization ellipse axis can be found by direct measurements of the phase shift, and the accuracy of measuring the ellipticity coefficient is affected only by the error of measuring the ratio of voltage amplitudes, which are proportional to the modules of the field strength vectors of the left and right directions of the circular polarization rotation. This provides better potential accuracy of measurement for the electromagnetic wave parameters when using circular polarization antennas and, correspondingly, more reasonable analysis in the circular orthogonal polarization basis.

This article is devoted to the analysis of prospect to apply multifunctional adaptive antenna systems for radio monitoring stations. The review of publications done demonstrates that current antennas that are developed and used in radio monitoring systems to control and measure the parameters of electromagnetic radiation should be applicable to conduct accurate measurements in wide frequency range under the condition of interferences. The analysis shows that modern adaptive antenna systems are mostly developed for radar and telecommunications applications. In this context we consider possible ways to solve the problem of adapting radio monitoring devices to a complex electromagnetic environment using antenna systems with primary processing of received signals . It was found that the developers of the antennas, which are based on adaptive interference suppression methods, focus basically on the development and implementation of adaptation processes, limiting themselves only to solving electromagnetic compatibility problems. In such approach, the functions of direction finding and measurement of radiation field parameters important exactly for radio monitoring systems are mostly ignored. Therefore, this research area opens up a wide field for identifying new possibilities for constructing multifunctional antenna systems. Focusing on this direction of research, we consider as an example the constraction of a simple two-element adaptive antenna system, which can be used to measure the parameters of the electromagnetic field in radio monitoring systems. The main relations for the error of determining the direction of arrival of the interference signal with a simple two-element antenna are investigated. The influence of the stability of the antenna array parameters and functional units of signal processing onto the errors is estimated.