To solve the real-time through-wall detection problem in the presence of wall ambiguities, an approach based on the kernel extreme learning machine (KELM) is proposed in this paper. The wall ambiguity and propagation effect are included in the single-hidden-layer feedforward networks, and then the technique converts the through-wall problem into a regression problem. The relationship between the scattered data and the target properties is determined after the KELM training process. Numerical results demonstrate the good performance in terms of the effectiveness, generalization, and robustness. Compared with the support vector machine (SVM) and least-squares support vector machine (LS-SVM), the KELM provides almost the same estimated accuracy but at a much faster learning speed, which greatly contributes to solving the real-time detection problem. In addition, the situations of two targets, different target radiuses, and noisy circumstances are discussed.
This paper presents the simultaneous application of Minkowski fractal geometry and EBG structures for mutual coupling reduction in microstrip array antennas for the first time. In this approach, a modified version of Minkowski fractal geometry is applied on the patch elements, and at the same time 1D electromagnetic bandgap (EBG) structures, composed of 4 EBG elements, are placed between the array elements in a very close distance. Unlike many other coupling reduction methods, which have at least one of the issues of gain reduction or complex fabrication, the proposed method does need any via or double-sided etching and slightly increases the gain of the antenna, while an excellent reduction level of 23 dB has been achieved. To verify the concept, 2 array antennas with the spacing of λ0 and λ0/3 were fabricated and tested, showing very good agreement between predicted and measured results.
A wideband high gain circularly polarized (CP) rectangular dielectric resonator antenna (RDRA) having a frequency range of 21 to 31 GHz is proposed. The RDRA consists of two layers with different dielectric permittivities and has been excited using a cross slot aperture. The proposed antenna offers wide impedance and CP bandwidths of ~36.5% and 13.75% respectively, in conjunction with a high gain of ~12.5 dBi. Close agreement has been achieved between simulated and measured results.
In this paper, an auxiliary differential equation (ADE) transmission line method (TLM) is proposed for broadband modeling of electromagnetic (EM) wave propagation in biological tissues with the Cole-Cole dispersion Model. The fractional derivative problem is surmounted by assuming a linear behavior of the polarization current when the time discretization is short enough. The polarization current density is approached using Lagrange extrapolation polynomial, and the fractional derivation is obtained according to Riemann definition of a fractional α-order derivative. Reflection coefficients at an air/muscle and air/fat tissues interfaces simulated in a 1-D domain are found in good agreement with those obtained from the analytic model over a broad frequency range, demonstrating the validity of the proposed approach.
Present contribution introduces, for the first time, the description of human exposure dynamics to mobile phone radiation by implementing the use of in-air integrated energy density (IED) evolution in time. Using the amplitude probability density (APD) function capability of a real-time spectrum analyzer, we demonstrate the differences in exposure due to five different mobile applications running in Long Term Evolution (LTE) standard, based on energy deposited in air: voice call; voice over LTE (VoLTE); video call, file download and live streaming. This exposimetric method will be of great interest also for the new 5G communication standard. The superiority of the approach has three branches: a) integrated APD allows a sample rate of the order of 0.6 x 108/s which is equivalent to an extremely agile tracing of the power level change in LTE communication standard (happening at every 6.67 μs); b) momentary and mean IED accumulation rate can be computed, and minute differences between mobile applications may be observed during their running time; c) the superficial tissue temperature increase may be rapidly estimated after the period of use of one specific wireless application in the GHz frequency range. The method implemented here also provides the means for rapid usage profile expectancy assessment of a mobile phone user.
A T-shaped feed based differential microstrip bandpass filter (BPF) with high common-mode (CM) rejection ratio is presented. The filter comprises two magnetically coupled conventional square open-loop resonators (SOLR), with capacitive coupled T-shaped input-output (I/O). The choice of the T-shaped I/O coupling feed enables a higher common-mode suppression of -57 dB at f0d that extends up to 4.1f0d with a value better than -30 dB. Frequency f0d is the cutoff frequency of the differential-mode (DM) passband. Moreover, this feed can symmetrically position two transmission zeros (TZs) at the upper and lower stopbands. This yields a highly selective and compact filter. Additionally, a T-shaped feed only excites the odd mode of the filter resulting in a wide stopband with high out of band rejection. The upper and stopband rejection of the filter is better than -50 dB. To demonstrate the design, DM and CM lumped models of the filter are proposed and studied. The filter operates at 1.263 GHz with a fractional bandwidth (FBW) of 3.9%. The design is validated experimentally by characterizing DM, CM, common-mode to differential-mode (CD), and differential-mode to common mode (DC). Moreover, the group delay (GD) response of the filter is measured, and a significantly flat response is observed with a maximum delay variation of only 0.88 ns in the 3 dB bandwidth.
An applicable and convenient method is critical for calculating the RCS (Radar Cross Sections) of chaff clouds. An improved method based on direct method  is proposed in this paper to promote efficiency, which is called SPMDM (Singular Points Meshing Direct Method). The tanh-sinh method is applied in SPMDM to compute the complex singular function in which the integral domain is meshed by the singular points. The practicability and accuracy of the SPMDM are confirmed through comparison with direct method. Results indicate that the SPMDM can significantly decrease calculation time and increase computing efficiency, especially in large-scale case or small relative error region.
Time domain reflectometry is frequently used to localize faults in electrical systems. Most existing literature on reflectometry in transmission lines considers symmetric faults that are either shorts between the two conductors or open circuits where both conductors are disconnected at the same location. This paper investigates spread spectrum time domain reflectometry (SSTDR) applied to asymmetric twin-lead transmission lines in which either only one conductor is disconnected or the reflectometry instrument itself is asymmetric. For asymmetric faults, we observe not only the expected dominant reflection corresponding to the location of the disconnection, but also an additional reflection from the end of the transmission line. In the second case, we leverage the asymmetric response of the SSTDR instrument to identify which of the two otherwise identical conductors has been disconnected.
The present work describes a unique planar wideband circularly polarized MIMO antenna for 4G and sub-6 5G band (1.35-2.6 GHz), with pattern diversity over the entire axial-ratio bandwidth. The design consists of two tri-branch planar inverted-F antenna (PIFA) antennas with a ground T-stub between the antennas, which is used to realize circular polarization and high isolation. The third antenna is an integrated sub-6 5G (4.45-4.7 GHz) and LTE band (786.7-807.7 MHz) antenna, which is folded above the ground and placed vertically around the side. It also provides circular polarization at LTE band. The 3 dB axial ratio bandwidth (ARBW) of the MIMO antenna is 1.05 GHz (1.47-2.52 GHz); impedance matching bandwidth (IMBW) is 1.25 GHz (1.35-2.6 GHz); and its isolation is better than 13.4 dB in the whole band. It has fabricated on an FR-4 substrate and is suitable for mobile handset.
A novel wideband microstrip patch antenna with nonuniform transmission line feed is presented using model predictive control. Nonlinear model predictive control (NMPC) is used to achieve a nonuniform transmission line that matches with the microstrip patch antenna. The transmission line is extended using cosine expansion with the impedance differential equation then being used as the dynamic NMPC equation to find the unknown coefficients of that cosine expansion. The transmission line is designed such that the impedance of the input port matches the impedance of the microstrip antenna at the resonance frequency and its adjacent frequencies. The proposed antenna's impedance is 5.15-5.85 GHz. In this bandwidth, the radiation pattern is stable; the cross polarization and back lobe are -30 dB and -20 dB respectively. The error in the impedance bandwidth is about 4.2%. The simulation and measurement results are considered satisfactory.
An effective and precise approach to the Wave Concept Iterative Process method modeling of magnetized graphene sheet as an anisotropic conductive surface is used to analyze the anisotropy of magnetostatically biased graphene and for studying an electrically doped magnetically biased graphene non-reciprocal antenna array for THz applications. The tuning of the performance of the array antenna is possible by varying the magnetic field and the chemical potential of graphene material. The return loss value decreases by increasing the magnetostatic bias and increases when the chemical potential increases.
This paper presents a miniaturized quintuple band antenna for multiband operation with the aim of developing a small and simple structure antenna that can operate at multiband frequency. The proposed antenna contains a rectangular microstrip patch, a transmission line with 50 Ω coplanar wave guide (CPW) and six L-slots. By introducing these L-slots along the X and Y axis, in the radiating element, the antenna yields five resonance modes at 2.4, 3.5, 4.4, 6.09, and 7.7 GHz while keeping the size of 27.4 x 24 mm2. The prototype of the proposed antenna is constructed and experimentally studied. The measured and simulated results prove that the proposed multiband antenna is suitable for Bluetooth, WLAN, WIMAX, LTE, and X band applications. The antenna is designed using FR4 lossy substrate material with relative permittivity εr of 4.4 and thickness of 1.6 mm.
A coplanar waveguide (CPW)-fed flexible dual-band antenna using graphene as conducting material and Kapton polyimide as a substrate is proposed. The antenna shows increased impedance bandwidth due to the use of CPW-feed having the values of 80.29% (1.64-3.84 GHz) and 6.31% (5.52-5.88 GHz), respectively. The antenna has an overall size of 0.38λ × 0.43λ at center frequency of 3.4 GHz. The proposed flexible antenna has gain values of 1.82 dBi and 1.68 dBi with efficiency values more than 86% which makes the antenna commercially viable for smart wireless products having space constraints.
A filtering rectangle dielectric resonator antenna (DRA) with high band-edge selectivity is proposed in this paper. The DRA is fed by a simple hybrid feeding structure consisting of a microstrip-coupled slot on the bottom and a thin metallic strip on the side of DRA to excite the fundamental TEy1δ1 mode. The feeding structure establishes a cross-coupled mechanism which includes electric and magnetic coupling; thus, introducing two radiation nulls at the band edge without any filtering circuits. By using the designed hybrid feeding structure, a bandpass filtering response is obtained. For enhancing band-edge selectivity, a shorted stub is introduced to weaken the coupling between the two microstrip stubs of the feeding structure. A wide impedance bandwidth of 19% and a flat gain of around 5.6 dBi are realized. To validate the design, a prototype is fabricated and measured, showing a favorable agreement with the simulated results.
In this article, we design a reconfigurable bandwidth based on a concentric ring slot antenna using graphene. The developed antenna has good agreement between simulated and experimental results. The use of graphene in Terahertz (THz) has shown better performance than metal, and the variation in the chemical potential of graphene provides excellent performance properties, good return loss reaching -33.288 dB, bandwidth reconfiguration from 255 GHz to 406 GHz, and a good gain. These results are promising for THz applications and particularly for the application of medical imaging. The modeling and validation are performed using the CST Simulator.
The proposed antenna structure is excited for multiple operational modes by means of meandered strips. The compact planar monopole antenna is demanded enormously for handheld devices especially automatic meter reading and tablet devices. Due to Chu limit, it is extremely vital to miniaturize an antenna by balancing tradeoff between bandwidth and radiation efficiency. The designed antenna is formed by two interconnected broad monopole open slots which covers multi-bands for smart energy meter and tablet computer applications. The cost effective FR4 laminate of size 50 x 200 mm2 (0.4λ x 1.6λ) is employed to match standard tablet computer communication module dimensions. The impedance bandwidth, for all excited resonant modes, is above typical requirement of 2%, and the VSWR is well below the necessary requirement of 1.5. The peak gain ranges from 0.94 dBi to 1.92 dBi. Radiation patterns along with other antenna parameters are satisfactorily meeting the demand of Wireless Energy Meter and Tablet Devices. The effects of varying dimensions of a monopole on the radiation characteristics have also been presented. The return loss and radiation patterns computed through simulations are validated through experimental measurements in an anechoic chamber environment.
The problem of impedance synthesis of two-dimensional diffraction arrays of thin linear vibrators, whose geometric centers are located at the nodes of a flat rectangular grid with double periodicity is solved analytically. The problem is formulated as follows: the complex surface impedances of the vibrators should be determined which allows to steer the diffraction radiation maximum of the array to any predefined direction. The problem is solved under following assumptions: array is excited by a polarized plane wave, and the radiation pattern (RP) of each vibrator element in the array coincides with that of an isolated radiator. The correctness of the solution is verified by simulations using the formulas for the vibrator impedances for the 5 by 5 antenna array.
This paper highlights the effect of millimeter wave (MMW) radiation on biological tissue for prolonged exposure to record thermal effects. The novel method described in this article isthe exposure of millimeter wave on the tissues and study the heat effects resulting from radiation. To simulate this, a setup to uniformly irradiate a tissue of about 2.2 mm thickness is described, and 3D visualization of MMW propagation is modeled using COMSOL Multiphysics radio frequency module at frequencies around 30 GHz. Heat generation and consequent temperature rise in the three layer tissue structure is followed by analysis of temperature variation due to radiation absorption.
This paper presents a novel quintuple-mode wideband lter based on a circular Substrate Integrated Waveguide (SIW) cavity. To implement this filter, a pair of two metallic perturbation vias loaded around the diameter resonator line is used. An Elliptic Dielectric Resonator (EDR) was introduced in the middle of the cavity to shift certain resonant modes and restrain the higher-order modes. The optimal dimensions and dielectric permittivity of the EDR are investigated. A single SIW resonator filter has been designed, manufactured, and measured as an experimental example to verify the proposed design. Simulation and measurement results agree with 51.7% of fractional bandwidth at 10.1 GHz central frequency, with one transmission zero (TZ) at the lower frequency side and four TZs at the upper side.
In this article, a design of two low-profile multiple-input-multiple-output (MIMO) antenna arrays based on left-handed metamaterial (LHM) structures is proposed for multiband wireless applications. The single-element antenna is a monopole antenna fed by a microstrip transmission-line loaded with a single LHM unit cell. The LHM unit cell structure consists of a right-angled bend interdigital capacitor and dual symmetrical right-angled bend shorted stub inductors. The loaded monopole antenna was previously designed to operate in the left-handed (LH) frequency region at three negative-order resconance modes (i.e. 1.39, 1.88, and 2.35 GHz). Herein, to increase the designed antenna performance in wireless communication systems, two- and four-element MIMO antenna arrays having compact sizes with overall dimensions of 21 × 35 mm2 and 35 × 35 mm2, respectively, are realized. A close uniform edge-to-edge separation between antenna elements of each configuration equals only 2 mm (0.0093λ0 at 1.39 GHz), and port isolation less than -18 dB over the entire operating bands is obtained without using extra isolation structures. Envelope correlation coefficient is evaluated, showing good field isolation. The performance of the assembled MIMO antenna arrays is verified numerically and experimentally. The given attributes make the proposed antenna arrays a suitable candidate for multiband MIMO applications.