V.V. Razevig – Ph.D. (Eng.), Senior Research Scientist, 

Bauman Moscow State Technical University

Е-mail: vrazevig@rslab.ru

А.S. Bugaev – Dr.Sc. (Phys.-Math.), Professor, Academician of RAS, Head of Department,

Moscow Institute of Physics and Technology (State University)

A.V. Zhuravlev – Ph.D. (Phys.-Math.), Leading Research Scientist,

Bauman Moscow State Technical University

М.А. Chizh – Ph.D. (Phys.-Math.), Senior Research Scientist,

Bauman Moscow State Technical University

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. Obtaining radar images in these applications is based on processing phase and amplitude of the reflected signal recorded over an aperture (a microwave hologram).

The phase center of an antenna is a virtual source point, which represents the origin of the radiated field from where the spherical divergence appears to be initiated. For real antennas such as arrays, reflectors, horns, and others, there is no single ideal phase center, its position is frequency-dependent. In addition, when an electromagnetic wave propagates from the transmitter output port to the antenna phase center and from the antenna phase center to the receiver input port, an additional phase incursion occurs: both in the antenna itself and in the feeders. The image reconstruction algorithms available in numerous publications usually omit the problem of antenna calibration. But disregarding the dependence of the antenna phase center position on frequency and phase incursion in the antenna-feeder path results in poorly reconstructed images. This problem gets more significant as the frequency bandwidth broadens.

In this work, the calibration problem is illustrated on simulated microwave holograms. For solving the problem, a new approach is proposed, which is based on acquiring and analyzing a wide-band multi-frequency microwave hologram of a point object. The research aimed at obtaining the calibration data, using which for hologram correction before its reconstruction brings the quality of resulting images close to the theoretical limit.

Test experiments were carried out using a measurement system composed of the following components: a compact vector network analyzer (VNA), two mechanical scanners with stepper motors, one transmitting and one receiving horn antennas, mounted on the VNA, a microcontroller board, and a computer. The experiments have shown that proposed method allows considerably increasing the quality of the reconstructed microwave images.

Razevig V.V., Bugaev А.S., Zhuravlev A.V., Chizh М.А. Calibration of the antenna-feeder path of microwave imaging systems. Achievements of modern radioelectronics. 2020. V. 74. № 7. P. 5–17. DOI: 10.18127/j20700784-202007-01. [in Russian]

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