V.V. Razevig¹, A.S. Bugaev², S.I. Ivashov³, A. Kizilay⁴

¹ Bauman Moscow State Technical University (Moscow, Russian)

² Moscow Institute of Physics and Technology (Moscow, Russian)

⁴ Yildiz Technical University (İstanbul, Turkey)

Microwave imaging technique allows obtaining images of hidden objects in a structure or media using microwaves. Recently, this technology has been increasingly used for non-destructive testing of various materials, including heat-insulating materials. The ability of a microwave imaging system to detect low-contrast defects (mainly voids) in the thickness of the heat-insulating material essentially depends on the characteristics of the antennas used in the system. The aim of this work is to compare two types of antennas (an open-ended circular waveguide antenna and a rectangular horn antenna) in terms of the quality of the received microwave images. The comparison was carried out both by computer electrodynamic modeling using the FEKO program and experimentally. Antennas characteristics such as VSWR (Voltage Standing-Wave Ratio) and width of a radiation pattern were measured, and the quality of the microwave radio images was estimated. Summary

Microwave imaging technique allows obtaining images of hidden objects in structures and media using microwaves. This technique has various applications such as: nondestructive testing, medical imaging, concealed weapon detection, through-the-wall imaging, etc. Recently, this technology has been increasingly used for non-destructive testing of heat-insulating materials.

Currently, one of the most pressing problems is the search and creation of energy-saving engineering solutions for the creation of heat and technological processes with minimal heat losses. The quality of the used thermal insulation materials plays an important role in this. During operation, defects or deterioration in the characteristics of thermal insulation occur. Depending on the field of application, such defects can even lead to death, as in the case of thermal protection of spacecraft.

As sensors in systems for non-destructive testing of thermal insulation materials, either rectangular horn antennas or open-ended circular waveguide antennas are often used.

This work is devoted to the theoretical and experimental comparison of these two types of antennas in the diagnosis of the same materials. In what follows, for brevity, a rectangular horn antenna will be called a horn antenna, and an open-ended circular waveguide antenna will be called a cylindrical antenna.

The cylindrical antenna was designed according to antenna theory, then optimized with the FEKO electromagnetic simulation program and fabricated. The horn antenna was available, therefore, to compare the antennas by the method of computer simulation, its geometric dimensions were measured and a model was built. Physical experiments were carried out using a Rohde & Schwarz ZVA 24 vector network analyzer.

At the first stage of comparison, the VSWR and antenna patterns were obtained by simulation, and then measured experimentally. In the experiment, the directional properties of the antennas were estimated from the amplitude microwave hologram of a thin spoke oriented perpendicular to the recording line of the microwave hologram. It turned out that the cylindrical antenna has a slightly wider radiation pattern (according to experimental data, the width is 60°) than the horn antenna (53°). As for the VSWR, according to the measurement data, for the cylindrical antenna, the maximum value in 20–24 GHz frequency range is 2.41, and the average is 1.71.

For the horn antenna, these values are 1.32 and 1.17, respectively, which indicates the advantage of the horn antenna.

At the second stage, the criterion for comparing antennas was the quality of microwave images obtained by reconstructing microwave holograms of a specially made test sample, which is a sheet of polyurethane foam with cutouts of various shapes and depths. To register microwave holograms, the principle of inverse aperture synthesis was used, when the antenna is stationary, and the object moves past it using a two-coordinate electromechanical scanner. Comparison of the obtained microwave images showed the advantage of the horn antenna, which provides a greater contrast of the objects to be detected (cutouts) in relation to the background of the microwave images.

Разевиг В.В., Бугаев А.С., Ивашов C.И., Кизилай А. Теоретическое и экспериментальное сравнение различных антенн при их использовании в системах радиовидения // Электромагнитные волны и электронные системы. 2021. Т. 26. № 6. С. 5−16. DOI: https://doi.org/10.18127/j15604128-202106-01

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