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ISSN 1805-9600 (Online)

Radioengineering

Radioeng

Proceedings of Czech and Slovak Technical Universities

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September 2019, Volume 28, Number 3 [DOI: 10.13164/re.2019-3]

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M. Barbuto, A. Bassotti, A. Alu, F. Bilotti, A. Toscano [references] [full-text] [DOI: 10.13164/re.2019.0499] [Download Citations]
On the Topological Robustness of Vortex Modes at Microwave Frequencies

Vortex fields carrying orbital angular momentum are robust with respect to a wide range of external disturbances and exhibit self-healing properties. These peculiar characteristics have been deeply investigated at optical frequencies but only a few of them have been observed at microwaves. In this paper, we try to partially fill this gap by investigating the topological characteristics of vortex fields radiated by standard patch antennas. In particular, we describe the behavior of a vortex mode when a metallic screen is placed in the near field of the radiating patch. Through a proper set of full-wave numerical simulations, we show that the main characteristics of the vortex mode, i.e. the spiral phase profile and the amplitude null, are preserved even if the overall radiated field is strongly perturbed by the obstacle.

Keywords: Phase singularities, vortex modes, antenna radiation pattern

Z. Sipus, Z. Eres, D. Barbaric [references] [full-text] [DOI: 10.13164/re.2019.0505] [Download Citations]
Modeling Cascaded Cylindrical Metasurfaces with Spatially-Varying Impedance Distribution

Modeling curved metasurface structures represents a computing challenge due to the complexity of considered designs. This creates a need for specialized efficient analysis methods. An approach that combines the spectral-domain field representation and surface sheet impedance concept is proposed. The considered cascaded cylindrical metasurface structures can span across only a part of a canonical surface and unit cell elements can vary along the metasurface, giving a spatially-varying sheet impedance. The analysis method is experimentally verified against a cylindrical metasurface for shaping the feed antenna beam. The problem of manufacturing curved metasurfaces is also discussed in the paper.

Keywords: Metasurfaces, curved metasurfaces, spectral domain approach, sheet impedance, metasurface production technology, high-frequency conductive materials

S. Costanzo, G. Lopez [references] [full-text] [DOI: 10.13164/re.2019.0512] [Download Citations]
Phaseless Single-Step Microwave Imaging Technique for Biomedical Applications

In the present work, an improved phaseless approach to microwave imaging is presented. Starting from the Contrast Source formulation of the scattering problem, a single-step procedure with no intermediate phase-retrieval process is described. The reconstruction capabilities of the proposed phaseless inverse method are numerically validated by firstly considering simple dielectric targets. Then, a slice breast model with the inclusion of a cancerous portion is analyzed. The identification of different types of breast tissue is successfully achieved, thus confirming the validity and potentialities of the proposed phaseless technique in the framework of biomedical imaging.

Keywords: Electromagnetic (EM) inverse scattering problem, Phaseless Contrast-Source Inversion method (P-CSI), breast imaging

D. Kuratko, D. K. Wojcik, J. Lacik, V. Koudelka [references] [full-text] [DOI: 10.13164/re.2019.0517] [Download Citations]
Electromagnetic Modeling of Rat’s Head: Comparison of Formulations and Models

Reliable inverse imaging of source currents in rat’s brain requires sufficiently accurate and CPU-time moderate forward models of fields to calibrate inverse solvers. In this paper, we compare different mathematical formulations of the electromagnetic problem related to the analysis of brain waves (static, quasi-static, full-wave) and various meshes differing in the density, the type and the geometrical accuracy. A sufficiently accurate model of brain waves is then completed by the cerebrospinal fluid and the skull. The resultant composite model of rat’s head with properly set electrical parameters has to be calibrated by the outputs of measurements. That way, a realistic electromagnetic model of the head of a live rat can be obtained.

Keywords: Forward brain model, rat’s head, numerical analysis, Maxwell equations.

H. Taghizadeh, Ch. Ghobadi, B. Azarm, M. Majidzadeh [references] [full-text] [DOI: 10.13164/re.2019.0528] [Download Citations]
Grounded Coplanar Waveguide-fed Compact MIMO Antenna for Wireless Portable Applications

A multi-input multi-output (MIMO) antenna with high isolation capability is proposed in this paper. The proposed MIMO antenna configuration is composed of two monopole antennas, each of them consists of a single rectangular grounded coplanar waveguide (GCPW) feed line, a radiation patch with two arms, two conductive elements on both sides of the feed line, and a simple ground plane on substrate backside. The overall size of the proposed MIMO antenna is 44×20 mm2 on 1.6 mm thick FR4 substrate which is more compact than many of the previously designed structures. The arrangement of two monopole antennas in the form of a MIMO antenna topology yield a dual-band operation in which the first bandwidth is in 3.06-3.89 GHz with the central frequency at 3.5 GHz for WiMAX applications, and 5.14-5.93 GHz with central frequency of 5.5 GHz for WLAN applications. Interestingly the obtained isolation level is better than -20 dB over the operating bandwithds. Simulation and measured results confirm the antenna outperformance in WiMAX and WLAN frequency range in wireless portable applications. Small size, simple structure, and high isolation without any decoupling elements are some of the advantages of the proposed design.

Keywords: Monopole antennas, multiple-input–multiple-output (MIMO), WiMAX applications, WLAN application, wireless portable devices

S. Pradhan, B. Gupta [references] [full-text] [DOI: 10.13164/re.2019.0535] [Download Citations]
Multiport Network Model of Double–stub Loaded Microstrip Ring Antenna for Tri–band Operation

A microstrip ring antenna has a single broadside fundamental radiating mode. In this communication one of the arms of the ring has been loaded with two stubs, so that the perturbation in the fields results in broadside radiation in the next two higher order modes. This results in three broadside radiating modes. Gap coupled excitation is chosen to achieve impedance matching in all the three frequency bands. Linearly polarized radiation with gain of 2.88 dB, 4.67 dB and 6.07 dB and half-power beamwidth of 89.6°, 76.3° and 79° in the φ=90º plane has been achieved at the center frequencies of 0.9526 GHz, 1.833 GHz and 2.468 GHz respectively. This structure has been analyzed using multiport network modeling. The modeling is vindicated by experimental results.

Keywords: Broadside radiation, gap–coupling, microstrip ring antenna, multiport network model

A. Das, J. Acharjee, K. Mandal [references] [full-text] [DOI: 10.13164/re.2019.0544] [Download Citations]
Compact UWB Printed Slot Antenna with Three Extra Bands and WiMAX Rejection Functionality

A compact ultra-wideband (UWB) printed slot antenna with additional bands of 870-960 MHz, 1.67-1.84 GHz, 2.33-2.57 GHz for GSM-900, GSM-1800 and Bluetooth respectively along with WiMAX band rejection functionality at 3.27-4.02 GHz is presented for various wireless applications. A simple circular patch fed by a trapezoidal-shaped microstrip line is conceived to cover entire UWB (3-10.5 GHz). Three additional bands have been accommodated by incorporating two pairs of spider arm-shaped resonators at the top of the slotted ground. Coupling between the extended feed line and extended back resonator is used to acquire a stop band characteristic for the reduction of possible interference between WiMAX and UWB bands. Moreover, an arc-shaped resonator and a cross-shaped slot on the feed line are conceived to enhance the bandwidth of the UWB. The proposed design is simple in structure and compact with an overall dimension of 50×50×1.6 mm3, hence length is only 0.046λ with respect to the lower edge frequency (3 GHz) of the UWB. The simulated and measured results are in good agreement that ensures the potentiality of the proposed antenna structure for UWB and multiservice wireless applications.

Keywords: UWB, printed antenna, extra bands, band rejection, GSM-900, WiMAX

A. Ghosh, A. Banerjee, S. Das [references] [full-text] [DOI: 10.13164/re.2019.0552] [Download Citations]
Design of Compact Polarization Insensitive Triple Bandstop Frequency Selective Surface with High Stability under Oblique Incidence

This paper proposes a novel design of a triple band frequency selective surface (FSS) that acts as a bandstop filter at 1.92 GHz, 3.5 GHz and 5.64 GHz. The bandstop frequencies resemble to GSM, WLAN and WiMAX application bands respectively. The structure is polarization insensitive since its frequency response remains unaltered for both TE and TM modes of electromagnetic wave propagation. The main attractive feature of the structure is its highly stable response under oblique incident angle upto ± 800 at both TE and TM polarizations. Surface current distribution and equivalent circuit modelling are presented to demonstrate the resonance characteristic of the FSS. The structure is compact with an overall unit cell area of 0.09λ x 0.09λ, where λ is the wavelength corresponding to the lowest resonant frequency. The proposed structure is compared with other multi-bandstop FSS structures in literature to highlight its superior functionality in terms of stability under oblique incidence and compactness. A prototype comprising of 6 x 6 array of the proposed unit cell is fabricated and the measured results are in good agreement with the simulated results.

Keywords: Frequency selective surface, bandstop filter, polarization insensitive, oblique incidence angle, compact

A. Banerjee, S. Chatterjee, B. Gupta, A. K. Bandyopadhyay [references] [full-text] [DOI: 10.13164/re.2019.0559] [Download Citations]
Analysis of Uniform and Tapered CPW-fed Zigzag Monopoles Used as Feed Structures for Wide-Slot Radiators

CPW-fed zigzag monopole radiators can be used to excite wide slots etched on the CPW-grounds for gain enhancement purposes, without significantly altering its resonance. The circuit analysis for CPW-fed zigzag monopole acting as a feed to a wide square slot is presented. Later, the uniform zigzag feed is tapered to support a gradual propagation constant modification. In both cases, the zigzag feed is conceived as an array of two constituent monopoles fed from the same source with modified propagation constants. Simulations along with the measured results are provided to validate the theoretical work which showed less than 2% error achieved in the predictions. Measured gains of the radiators are reported at their resonance frequencies, 2.93dB and 3.19dB respectively for the uniform and tapered zigzag feeds, which validates the observation of gain enhancement in this article.

Keywords: Circuit model analysis, closed-form expressions, uniform and tapered zigzag monopole, Wide-Slot Radiator, Gain Enhancement

R. Agrawal, P. Belwal, S. C. Gupta [references] [full-text] [DOI: 10.13164/re.2019.0565] [Download Citations]
Half Mode Substrate Integrated Waveguide Leaky Wave Antenna with Broadside Gain Enhancement for Ku-Band Applications

A miniaturized frequency scanned leaky wave antenna (LWA) based on half mode substrate integrated waveguide (HMSIW) with open stop-band suppression is proposed. The modified cross-slot is etched on the top of HMSIW as the radiating element. The folded and unfolded ground plane designs of the proposed HMSIW LWA are compared and analyzed w.r.t their bloch impedance characteristics and it is found that further miniaturization and gain improvement at broadside by ~ 2dBi are achieved for folded ground plane design. The proposed LWA scans a region from -40° to +24° as the frequency range increases from 12 to 17 GHz with broadside at 15.5 GHz. The HMSIW LWA with folded ground plane is fabricated and its performance is experimentally measured showing the close agreement between the simulation and the measured results.

Keywords: Miniaturization, folded ground plane, half mode substrate integrated waveguide, broadside gain enhancement, leaky wave antenna

S. Koziel, A. Pietrenko-Dabrowska [references] [full-text] [DOI: 10.13164/re.2019.0572] [Download Citations]
Efficient Gradient-Based Algorithm with Numerical Derivatives for Expedited Optimization of Multi-Parameter Miniaturized Impedance Matching Transformers

Full-wave electromagnetic (EM) simulation tools have become ubiquitous in the design of microwave components. In some cases, e.g., miniaturized microstrip components, EM analysis is mandatory due to considera¬ble cross-coupling effects that cannot be accounted for otherwise (e.g., by means of equivalent circuits). These effects are particularly pronounced in the structures in¬volving slow-wave compact cells and their numerical opti¬mization is challenging due to expensive simulations and large number of parameters. In this paper, a novel gradi¬ent-based procedure with numerical derivatives is pro¬posed for expedited optimization of compact microstrip impedance matching transformers. The method restricts the use of finite differentiation which is replaced for se¬lected parameters by a rank-one Broyden updating for¬mula. The usage of the formula is governed by an ac¬ceptance parameter which is made dependent on the pa¬rameter space dimensionality. This facilitates handling circuits of various complexities. The proposed approach is validated using three impedance matching transformer circuits with the number of parameters varying from ten to twenty. A significant speedup of up to 50 percent is demon¬strated with respect to the reference algorithm.

Keywords: Microwave design closure, EM simulation, design optimization, trust-region framework, Broyden update, impedance transformers

G. W. Zhang, J. Gao, X. Y. Cao, H. H. Yang, L. R. Jidi [references] [full-text] [DOI: 10.13164/re.2019.0579] [Download Citations]
An Ultra-Thin Low-Frequency Tunable Metamaterial Absorber Based on Lumped Element

In this paper, an ultra-thin metamaterial absorber with a stretching transformation (ST) pattern is proposed and fabricated in the low-frequency range. The absorber is composed of dielectric layer, metal patch loading resistor and variable capacitor which produce its tunability. In order to expand the tunable bandwidth, we applied the ST with various coefficients x and y to the unit cell pattern. Measurement and simulated results show that the structure can be tuned to provide a continuously variable reflectivity level of less than -10 dB from 0.68 to 2.13 GHz at bias voltages of 10–40 V. The total thickness of this absorber was only λ/31 of the center frequency. Both measurements and simulated results indicate that this absorber can be thin and achieve a tunable absorption simultaneously.

Keywords: low-frequency, wideband, ultra-thin, ST coefficients, tunability.

S. Sheng, H. X. Chen, J. Wen, H. R. Liu [references] [full-text] [DOI: 10.13164/re.2019.0585] [Download Citations]
Simulation and Fabrication of Broadband Tunable Phase Shifter Based on Transmission Line Metamaterial

This paper presents a kind of broadband, low-loss tunable phase shifter based on transmission line metamaterial. An inherent high-pass backward-wave response property of a left-handed metamaterial based on coplanar waveguide (CPW) transmission line was used to realize a microwave phase shifter. The commercial software Ansoft HFSS was used to design and analyze for the transmission line metamaterial phase shifter structure, and the resulting S-parameters were used to characterize its performance. A transmission line metamaterial phase shifter was fabricated on Copper-Clad Board. The designed four unit-cells phase shifter provides a 0-190o continuous phase shift at 7.2 GHz using varactors biased from 0 V to 6 V with relatively low insertion loss.

Keywords: Transmission line metamaterial, tunable phase shifter, varactor, broadband

M. Gupta, D. K. Upadhyay [references] [full-text] [DOI: 10.13164/re.2019.0591] [Download Citations]
Design and Implementation of Fractional-Order Microwave Integrator

A novel design of fractional-order microwave integrator using shunt connected open-stubs with transmission line sections in cascade is proposed. Design is obtained by optimizing the L1-norm based error function in Z-domain having not more than absolute magnitude error value of 0.01. Optimization is done using nature inspired cuckoo search algorithm. Superiority of the design in terms of magnitude error performance is identified by comparing it with the results obtained from some widely used benchmark optimization algorithms. The obtained design is implemented on a RT/Duroid 5880 substrate having 20 mil thickness, and results for the measured magnitude response are found to be in good agreement with ideal one over the frequency range of 1.0 GHz to 6.8 GHz.

Keywords: Fractional-order, integrator, line elements, microwave, optimization

P. Vacula,V. Kote, D. Barri, M. Vacula, M. Husak, J. Jakovenko, S. Privitera [references] [full-text] [DOI: 10.13164/re.2019.0598] [Download Citations]
Comparison of MOSFET Gate Waffle Patterns Based on Specific On-Resistance

This article describes waffle power MOSFET segmentation and defines its analytic models. Although waffle gate pattern is well-known architecture for effective channel scaling without requirements on process modification, no until today precise model considering segmentation of MOSFETs with waffle gate patterns, due to bulk connections, has been there proposed. Two different MOSFET topologies with gate waffle patterns have been investigated and compared with the same on-resistance of a standard MOSFET with finger gate pattern. The first one with diagonal metal interconnections allows reaching more than 40 % area reduction. The second MOSFET with the more simple orthogonal metal interconnections allows saving more than 20 % area. Moreover, new models defining conditions where segmented power MOSFETs with waffle gate patterns occupy less area than the standard MOSFET with finger gate pattern, have been introduced.

Keywords: Power MOSFET, waffle MOSFET, specific on-resistance, integrated circuits

J. A. Jahanshahi, H. Danyali, M. S. Helfroush [references] [full-text] [DOI: 10.13164/re.2019.0610] [Download Citations]
A Modified Compressed Sensing-Based Recovery Algorithm for Wireless Sensor Networks

In this paper, a novel compressed sensing (CS) acquisition and joint recovery of spatiotemporal correlated signals algorithm is presented for effective data collection and precise sensors data streams reconstruction in wireless sensor networks. The CS-based proposed method utilizes~an iterative re-weighted l1-minimization and a l2 regularization to increase the reconstruction accuracy with a small number of required data transmission. Moreover, we develop~an alternating direction method of multipliers based algorithm to efficiently solve the resulting optimization problem. Numerical experiments are conducted on several test signals with~a variety of sampling ratios. The experimental results verify the effectiveness of the proposed scheme in terms of reconstruction accuracy and consumption time compared with the state of the art algorithms.

Keywords: Distributed compressive sensing (DCS), regularization, iterative re-weighted l1-minimization, wireless sensor networks

G. Liu, Y. Kang, H. Quan, H. Sun, P. Cui, C. Guo [references] [full-text] [DOI: 10.13164/re.2019.0618] [Download Citations]
The Detection Performance of the Dual-Sequence-Frequency-Hopping Signal via Stochastic Resonance Processing under Color Noise

Can the Dual-Sequence-Frequency-Hopping (DSFH) as a military emergency communication mode work under strong color noise? And is there any detection improvement of the DSFH signal via stochastic resonance (SR) processing under color noise? To deal with this problem, we analyze the physical feature of the DSFH signal. Firstly, the signal models of transmission, reception and the intermediate frequency (IF) are constructed. And the scale transaction is used to adjust the IF signal to fit the SR. Secondly, the non-markovian Langevin Equation (LE) is transformed into a markovian one by expand the 1-D LE to~a 2-D one. Thirdly, the non-autonomous Fokker-Plank Equation (FPE) is transformed into an autonomous one by assuming that the SR transition of magnetic particles is instantaneous and introducing the decision time. Therefore, the analytical periodic steady solution of the probability density function (PDF) with the parameter of the correlation time of the color noise is obtained. Finally, the detection probability, false alarm probability and Receiver Operating Characteristics (ROC) curve are obtained, under the criterion of the maximum~a posterior probability (MAP). Theoretical and simulation results show as below: 1) whether the DSFH can work under strong color noise is decided by the correlation time of the color noise; 2) when the power intensity of the color noise is constant, the smaller the correlation time with the bigger local SNR, the greater PDF difference of the SR output under two hypothesis, leading to better detection performance.

Keywords: Dual-Sequence Frequency Hopping, stochastic resonance, detection performance, color noise

W. K. Zhang, Q. P. Wang, J. J. Huang, N. C. Yuan [references] [full-text] [DOI: 10.13164/re.2019.0627] [Download Citations]
Two-dimensional Underdetermined DOA Estimation of Quasi-stationary Signals via Sparse Bayesian Learning

In order to improve the direction-of-arrival (DOA) estimation performance of quasi-stationary signals (QSS) using a uniform circular array (UCA), this paper addresses novel method in the context of sparse representation framework. Based on the Khatri-Rao transform, UCA can achieve a higher number of degrees of freedom to resolve more signals than the number of sensors. Then, by exploiting the two-dimensional (2-D) joint grid of UCA, the estimations of elevation and azimuth angles can be obtained from the sparse representation perspective. Finally, an expectation-maximization iteration method is developed to estimate DOAs of QSS from a Bayesian perspective. Since SBL makes full use of the sparse structure of QSS, thus the proposed algorithm possesses higher angular resolution and better DOA estimation precision compared with existing methods. Numerical simulation demonstrate the validity of the proposed method.

Keywords: Quasi-stationary signals, Underdetermined DOA estimation, Uniform circular array, Khatri-Rao transform, Sparse Bayesian learning

S. Tunc, H. A. Ilgin [references] [full-text] [DOI: 10.13164/re.2019.0635] [Download Citations]
Dim Target Detection in Infrared Images Using Saliency Algorithms

Infrared (IR) target detection and tracking are commonly used in modern defense systems. Target detection is the first and very important step for several surveillance applications. Long distance between imager and targets or bad weather conditions mostly cause dim target appearance with low signal-to-noise ratio (SNR) in IR images. In this study, dim targets in IR images are enhanced and detected using saliency detection algorithms, which have not been used in IR wavelength before. Performances of the algorithms are evaluated on common IR datasets. Algorithms are compared in terms of SNR, receiver operating characteristic (ROC) and area under curve (AUC) score. Effects of parameter selection are also considered for automatic target detection. Furthermore, feasibility of the methods for real-time applications are discussed.

Keywords: Infrared images, target detection, dim target, saliency

Z. Saavedra, J. N. Argota, M. A. Cabrera, A. G. Elias [references] [full-text] [DOI: 10.13164/re.2019.0643] [Download Citations]
A New Approach to OTH Main Parameters Determination

In this work, we propose a method based on a simulation that incorporates several models to provide the set of parameters needed on Over-The-Horizon radars (OTHR) performance evaluation, which consists in a versatile software tool. Obtaining the signals involved during transmission and reception is a complex and challenging task. Among them, the received signal is fundamental to design methods and algorithms in the target detection strategy. The parameters in the transmission and reception processes that define the radio link main features are determined in terms of target type, ionospheric conditions, radio link characteristics, and other environmental properties. The determination is done combining models to work assembled in a software tool that simulates the OTHR radio link. The tool gives the possibility of step away from the linear model, which uses mainly constant parameters and it is used commonly. A large number of set up parameters and also interconnections among several models enable to simulate nearer to actual search sceneries.

Keywords: OTH radar, clutter, ground range, MUF, radar cross section, ray tracing

S. R. Hou, Y. J. Zhou, H. M. Liu [references] [full-text] [DOI: 10.13164/re.2019.0651] [Download Citations]
Convolutional Neural Networks for Profiled Side-channel Analysis

Recent studies have shown that deep learning algorithms are very effective for evaluating the security of embedded systems. The deep learning technique represented by Convolutional Neural Networks (CNNs) has proven to be a promising paradigm in the profiled side-channel analysis attacks. In this paper, we first proposed a novel CNNs architecture called DeepSCA. Considering that this work may be reproduced by other researchers, we conduct all experiments on the public ASCAD dataset, which provides electromagnetic traces of a masked 128-bit AES implementation. Our work confirms that DeepSCA significantly reduces the number of side-channel traces required to perform successful attacks on highly desynchronized datasets, which even outperforms the published optimized CNNs model. Additionally, we find that DeepSCA pre-trained from the synchronous traces works well in presence of desynchronization or jittering after a slight fine-tuning.

Keywords: Side-channel analysis, deep learning, convolutional neural networks, DeepSCA

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