Volume 16 (2020): Edition 1 (January 2020)

The paper presents experimental diagnostics of the oil-paper insulating system of power transformers using progressive frequency method. The first part of the paper deals with the basic information about diagnostics of power oil transformers. The second part of the paper deals with the use of frequency domain spectroscopy (FDS) for power oil transformers. This method is used in the analysis of insulating condition of power transformer with the system of oil-paper. It was found that the results of these tests are highly influenced by the operating temperature during the experimental measurement. Moisture and conductivity between the insulating transformer paper and oil in an insulating system are highly dependent on the temperature. In the other part, the paper presents experimental results of the diagnostic measurement for a real traction oil transformer at different operating temperatures and states (with oil and without). Finally, the paper presents comparative measurement among several autotransformers with the same power. In experimental measurements, the correlation between the measured values and the operational aspects of the individual oil autotransformers are shown.

The accumulators utilized in electric transport differ from those of other applications. Their main features are high capacity, minimum size and weight, and reasonable price. There is extensive research worldwide to improve the battery technology. The aim of the research is to create a mathematical model of an electric vehicle that can capture the vehicle speed curve as a data input to generate the consumed and recovered battery current, which can allow the battery parameters to be analysed and conclude whether the vehicle can perform the trip around the city route with the selected battery parameters. This model serves as a tool to simplify and speed up the necessary calculations and to examine individual sections of the route and their impact on the battery. To complete this task, a simplified electric transport mathematical model gives an opportunity to check if the selected battery can be used in the electrical public transport of the city. The input parameters of the model are the parameters of electrical transport. Simulation of the most popular types of batteries has been performed for two routes of buses in Jelgava in order to determine whether the chosen batteries can provide the necessary bus movement. The mathematical model has been developed in the MATLAB/Simulink software. A GPS mobile application SpeedTracker has been used for data logging.

A novel design of ultra-wideband CPW-fed compact monopole patch antenna is presented in the article. The size of the antenna is 22 × 18 × 1.6 mm and it operates well over an ultra-wideband frequency range 4.86–13.66 GHz (simulated) and 4.93–13.54 GHz (measured) covering C, X and partial Ku band applications. The proposed design consists of a defected ground plane and U-shape radiating patch along with two square shape parasitic patches in order to achieve the ultra-wideband (UWB) operations. The performance matrix is validated through measured results that indicate the wide impedance bandwidth (93.2 %) with maximum gain of 4 dBi with nearly 95 % of maximum radiation efficiency; moreover, the 3D gain pattern manifests approximately omni-directional pattern of the proposed design. The prototype has been modelled using HFSS (High Frequency Structure Simulator-18) by ANSYS, fabricated and tested using vector network analyser E5071C.

The operation system determines the efficiency of the intended use of radio equipment. The operation system includes radio equipment, documentation, operational resources, personnel, processes, data processing algorithms, etc. The operation process is associated with conditions of priori uncertainty of models, parameters, external factors, etc. The main element for monitoring is technical condition of radio equipment. In a general case, this condition can deteriorate. The problems of technical condition deterioration analysis can be considered in terms of changepoint study. The present paper concentrates on the problem of synthesis and analysis of method for changepoint detection during radio equipment operation. The detection algorithm is constructed based on Neyman–Pearson criterion with sample size accumulation. During algorithm synthesis the thresholds were calculated according to Bellman’s approach. The problem of synthesis and analysis was solved by two methods: analytically and using statistical modelling. The efficiency measures for this algorithm are the probability of correct detection and mean time of decision making. The proposed algorithm has advantages in mean time of decision making compared with CUSUM detection method.

The present paper describes the development of a new technique for designing orthogonal bicomplex Digital Signal Processing (DSP) algorithms. In contrast to those previously reported on, this novel method is of universal application while being unaffected by either the type or the order of the real digital processing algorithm employed as a prototype. The proposed technique builds on Watanabe and Nishihara’s complex orthogonal transformation, and converts real or complex orthogonal transfer functions into bicomplex orthogonal ones. In this study, the new technique is applied to the design and testing of orthogonal bilinear bicomplex filters with a canonical number of elements, the main advantage of which is that they are several times lower in order. In this way, bilinear bicomplex orthogonal transfer functions are made up of real coefficient ones of the fourth-order, thereby reducing the order of the filter by a factor of four. The experiments demonstrate that the properties of the prototype filter are acquired by the bicomplex orthogonal filters, irrespective of the prototype being complex or real in nature.

The use of mobile data transfer can significantly increase the range of the remote-controlled operation of multirotor aerial vehicles. The planar antennas of ready-to-use 3G/LTE cellular communication dongles provide a low-cost and lightweight communication solution. In this paper, antenna shadowing caused by a quadcopter frame is experimentally investigated. The communication module is a 3G/LTE “Huawei 3372h” dongle with two planar built-in antennas and a receiver diversity function. The quadcopter frame is a widely used “F450” with Nylon arms and a PCB centre. It has been found that in order to minimize the antenna shadowing effect, planar antennas should be installed at the bottom of the frame, in parallel with the frame, with an air gap not less than the distance to the outer boundary of the reactive Near Field (NF).

The research paper presents a novel and compact circularly polarized (CP) antenna for a 5G wireless local area network (WLAN) application. It consists of a circular patch and a coaxial probe feed radiator. Circular polarization (CP) is attained by symmetric semi-circular slits of radius r₁ at three edges of a circular path with 90° in direction, and the other semicircular slit is of different radius r₂. To improve the impedance bandwidth and axial ratio, the radius of the fourth semicircular slit on circular patch antenna is varied. The design is verified by fabricating a compact antenna of 0.65λ₀ × 0.65λ₀ × 0.01λ₀. The measured 10 dB impedance bandwidth is 3.9 % (5.36–5.56 GHz), 3-dB axial ratio bandwidth is 1.1 % (5.43–5.49 GHz) and gain of 6.6 dBi at resonant frequency of 5.37 GHz is obtained. The authors also describe two-dimensional radiation patterns of azimuth and elevation plane surface current distribution of the CP patch, VSWR < 2. The proposed CP antenna is suitable for the 5G WLAN application. The proposed design is compared with various techniques in literature and tabulated. The measured results are also discussed and they are in good agreement with simulated results.

Meander structures allow reducing the size of the microwave devices while keeping the same operational characteristics. The shape of meander makes a considerable impact on the operation of microwave devices. Therefore, the structure of meander is widely investigated nowadays. The review of different shapes of a meander conductor is presented in this article. Two models with different shape of connecting conductors are designed and discussed in detail. The influence of variation of the length and width of connecting conductors on the electrical parameters of the meander is revealed using the traditional model of meander. Later, the comparison of the traditional model and the model with rectangle-shape peripheral parts of a meander conductor is presented. The increase in the width of connecting conductors from 0.2 mm to 1.0 mm has narrowed the bandwidth by 346 MHz until 2.388 GHz. The increase in the length of connecting conductors to 2.3 mm has allowed moving the stop-band to higher frequencies. The usage of the rectangle-shape connecting conductors slightly reduces the pass-band but allows achieving more stable input impedance.