Compact Radar Cross-Section Measurement Setup and Performance Evaluation

Radar cross-section measurements require the background reflections to be much lower than the reflections of the device under test. Although, anechoic chambers with special target holders meet this requirement, they are expensive and still have imperfections. To further reduce background reflections or to measure in environments where an anechoic chamber is not suitable, digital signal processing can be used to reduce background reflections. In this paper, a complete signal processing chain realized in Matlab is proposed, involving time gating of the measured target response and a background subtraction technique. Furthermore, the proposed signal processing includes a calibration procedure with either a single known calibration target or multiple known targets to improve measurement uncertainties. A compact measurement setup, consisting of a vector network analyzer and two horn antennas, is used to evaluate the overall performance and the advantages of a multiple known target calibration in a practical manner. The calibrated setup is able to measure the radar cross-section in a frequency range from 2 to 12 GHz with a mean error of less than 0.2 dB for both, VV and HH polarization combinations. It could also be shown, that a multi target calibration can result in an improvement of the measurement uncertainty by about 2.5 %.

Scattering Model-Based Frequency-Hopping RCS Reconstruction Using SPICE Methods

RCS reconstruction is an important way to reduce the measurement time in anechoic chambers and expand the radar original data, which can solve the problems of data scarcity and a high measurement cost. The greedy pursuit, convex relaxation, and sparse Bayesian learning-based sparse recovery methods can be used for parameter estimation. However, these sparse recovery methods either have problems in solving accuracy or selecting auxiliary parameters, or need to determine the probability distribution of noise in advance. To solve these problems, a non-parametric Sparse Iterative Covariance Estimation (SPICE) algorithm with global convergence property based on the sparse Geometrical Theory of Diffraction (GTD) model (GTD–SPICE) is employed for the first time for RCS reconstruction. Furthermore, an improved coarse-to-fine two-stage SPICE method (DE–GTD–SPICE) based on the Damped Exponential (DE) model and the GTD model (DE–GTD) is proposed to reduce the computational cost. Experimental results show that both the GTD–SPICE method and the DE–GTD–SPICE method are reliable and effective for RCS reconstruction. Specifically, the DE–GTD–SPICE method has a shorter computational time.

Influence of Environmental Noise on Quality Control of HVAC Devices Based on Convolutional Neural Network

Testing the quality of manufactured products based on their sound expression is becoming popular nowadays. To maintain low production costs, the testing is processed at the end of the assembly line. Such measurements are affected considerably by the factory noise even though they are performed in anechoic chambers. Before designing the quality control algorithm based on a convolutional neural network, we do not know the influence of the factory noise on the success rate of the algorithm that can potentially be obtained. Therefore, this contribution addresses this problem. The experiments were undertaken on a synthetic dataset of heat, ventilation, and air-conditioning devices. The results show that classification accuracy of the decision-making algorithm declines more rapidly at a high level of environmental noise.

AN ANECHOIC CHAMBER BUILT INTO INDUSTRIAL ROOMS

The issues of designing anechoic chambers for antenna measurements of a certain type – em-bedded in the premises of industrial purpose are considered. The advantage of such chambers is a positive economic effect associated with both the reduction of costs for construction work, and with the possibility of joint use of auxiliary room systems in the process of operation. Known ap-proaches to the design of chambers for antenna measurements are based either on ensuring a min-imum level of aesthetics, or minimum overall dimensions. In this case, it is necessary to provide a compromise between the parameters of anechoic stability and overall dimensions while ensuring the technological accessibility of the entire usable area of the room. Aim. The aim of the work is to justify the form and geometric dimensions of the chamber. Research Methods. In the process of re-search used the methods of geometric optics. When justifying the form of the chamber, practical aspects were taken into account, namely, the common form of industrial premises and workshops, as well as the possibility of effective use of common radio-absorbing materials to cover the cham-ber from the inside. In the process of finding the optimal effective geometric dimensions, the quality functionals were assumed to be aechoic and dimensional parameters. Results. A chamber in the form of a rectangular trapezoid is optimal for embedding in industrial premises. The expressions for the geometric dimensions of the chamber, ensuring the absence of first- and second-order reflections in the working area, have been found. The optimum value of the deflection angle of the back wall of the anechoic chamber was found. Conclusion. Based on the above technique, an anechoic chamber of a compact range for antenna measurements has been realized.

AFM study of changes in properties of horseradish peroxidase after incubation of its solution near a pyramidal structure

In our present paper, the influence of a pyramidal structure on physicochemical properties of a protein in buffer solution has been studied. The pyramidal structure employed herein was similar to those produced industrially for anechoic chambers. Pyramidal structures are also used as elements of biosensors. Herein, horseradish peroxidase (HRP) enzyme was used as a model protein. HRP macromolecules were adsorbed from their solution onto an atomically smooth mica substrate, and then visualized by atomic force microscopy (AFM). In parallel, the enzymatic activity of HRP was estimated by conventional spectrophotometry. Additionally, attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) has been employed in order to find out whether or not the protein secondary structure changes after the incubation of its solution either near the apex of a pyramid or in the center of its base. Using AFM, we have demonstrated that the incubation of the protein solution either in the vicinity of the pyramid’s apex or in the center of its base influences the physicochemical properties of the protein macromolecules. Namely, the incubation of the HRP solution in the vicinity of the top of the pyramidal structure has been shown to lead to an increase in the efficiency of the HRP adsorption onto mica. Moreover, after the incubation of the HRP solution either near the top of the pyramid or in the center of its base, the HRP macromolecules adsorb onto the mica surface predominantly in monomeric form. At that, the enzymatic activity of HRP does not change. The results of our present study are useful to be taken into account in the development of novel biosensor devices (including those for the diagnosis of cancer in humans), in which pyramidal structures are employed as sensor, noise suppression or construction elements.

THE EFFECTIVENNESS OF SOME PRACTICAL METHODS OF LOWERING THE BACKGROUND ACOUSTIC NOISE, PRODUCED BY THE ENGINE TEST BENCH TECHNOLOGICAL EQUIPMENT

When conducting acoustic researches and finishing works on combustion engines specialized technological equipment and tools mounted mainly in anechoic chambers are used. In order to ensure the high quality and objectivity of the research results of the sound fields produced by the research object it is crucial to achieve a sufficiently low parasitic background noise produced by technological equipment and tools of an engine test bench. The source of a high background noise re-emited to the anechoic chambers interior is structural vibrations of the solid objects of load carrying and flatsheet box-type structures of the bench. The article considers tested technical methods of improving vibroacoustics of load carrying and envelope structures of the engine test bench, which is in startup, commissioning and preliminary operation phase in the research center of a car manufacturer. Therewith there was a requirement to prevent any fundamental changes of the bench original basic construction, in order to minimize potential material and financial expenses for its reengineering process. Tested design solutions allow to reduce the level of parasitic noise disturbances, produced directly by the bench equipment in an anechoic chamber, up to 12 dBA.

Near-Field Antenna Measurements with Manual Collection of the Measurement Samples

Near-field measurements are commonly performed in anechoic chambers which limits the flexibility of the measurements and requires high precision equipment to achieve exact results. In this contribution, we investigate a simple near-field measurement setup which does not use any sophisticated positioning system nor operates in a controlled environment. Instead, the probe antenna is moved by an operator person while the probe position is measured by a laser tracker. This implies that the measurement results will have a higher error level in comparison with antenna chamber measurements. However, excellent error levels are not always necessary, especially when it comes to on-site testing of the principle functionality of antennas. Measurement results are shown to illustrate the performance of the system.