A four-element multiple-input multiple-output (MIMO) antenna based on a modified Complementary Split Ring Resonator (MCSRR) is presented in this paper for dual-band 5G smartphone applications. An inverted L-shaped radiator is used with MCSRR as an open stub in the ground, where MCSRR is responsible for dual operating bands and enhances the impedance matching. The MCSRR as an open stub in the ground plane creates a notch band that minimizes the interference in 5G wireless communication. The four elements of the antenna are placed in such a way that minimum isolation between antenna elements is obtained, 16.5 dB, without any decoupling, whereas more than 20 dB isolation is achieved by using T-shaped decupling. The antenna achieves dual 10 dB bandwidths from 3.40 GHz to 3.625 GHz and from 3.90 GHz to 4.525 GHz. Envelop correlation coefficient (ECC) is extracted from far-field results to analyse the MIMO antenna performance in practical design consideration.

This review discusses the evolution of the various radar cross-section (RCS) reduction techniques, with an emphasis on metasurfaces. The paper first introduces the terms RCS and RCS reduction and then discusses conventional and modern techniques to reduce RCS. The two main strategies used are scattering and absorption. The traditional methods of shaping and Radar Absorbing Material (RAM) are first briefly reviewed, followed by an extensive review of metasurface-based RCS reduction. RCS-reducing metasurfaces have the unique characteristics of acting as scatterers and absorbers. They are also described with regard to their passive and active configurations. The RCS reduction techniques are discussed with respect to profile, bandwidth, angular stability, polarization sensitivity, design complexity, and cost-effectiveness. A comprehensive comparison chart based on the performance parameters such as bandwidth, size and angular stability is tabulated for the different types of metasurfaces. The review also details areas that require further investigation.

This paper proposes a dual-beam switchable self-oscillating active integrated array antenna for Ku-band wireless power transfer systems. The oscillation is sourced by a positive feedback type Push-Push oscillator, which shows an excellent measured output power of +9.3 dBm obtained at the second harmonic frequency as well as good suppression of the undesired harmonics. The generated RF power from the oscillator excites four patch antenna elements. Moreover, a PSK modulator is adopted for binary phase switching between 0˚ and 180˚. Using in/anti-phase RF signal combination of the antenna elements, it is possible to switch between two beams, sum and difference radiation patterns. The proposed structure is fabricated and tested; the measured results verify the dual-beam switching concept with an effective isotropic radiated power (EIRP) of +17.77 dBm, DC-to-RF efficiency of 0.43%, and an oscillator figure of merit (FOM) of -158.05 dBc/Hz at the second harmonic frequency of 14.7 GHz.

This work is devoted to the development of a high gain Frequency Selective Surface (FSS) reflector backed monopole antenna using Machine Learning (ML) techniques for 5G applications. It analyzes and solves the complexity of the determination of the optimum position of the FSS reflector and the ground dimension of the monopole in this composite antenna structure since there are no solid and standard formulations for the computation of these two parameters. ML modelling is involved in the development process for the sake of gain enhancement. It is applied to get the optimum position of the FSS reflector layer and the ground dimension of the monopole antenna. The proposed antenna structure is 50 mm × 50 mm, implemented on a Rogers 5880 substrate (thickness = 1.6 mm). Two different patch antenna structures, with and without FSS, are developed and considered in the current work. The antenna performance in terms of operating frequency, return loss, and gain is analysed using the finite element methods. The design is optimized for a targeting frequency band operating at 6 GHz (5.53 GHz to 6.36 GHz), which is suitable for 5G Sub-6 GHz applications. The obtained results show that the integration of the FSS layer below the antenna structure provides a simple and efficient method to obtain a low-profile and high-gain antenna. Finally, the proposed design is fabricated and measured, and a good agreement between the simulated and measured results is obtained. A comparison with similar studies in the literature is presented and shows that the current design is more compact in size, and the obtained radiation efficiency and gain are higher than other designs.

An infrared (IR) pyroelectric detector for applying to the terahertz (THz) waveband that uses diffraction limited focusing of the THz beam on the sensitive area of the detector is studied. The signal to be detected is coupled to the optical window of the detector through a two-wavelength diameter polytetrafluoroethylene spherical particle-lens based on the terajet effect. We have experimentally demonstrated an enhancement of the IR detector sensitivity by 5.6 dB at 0.2 THz without degradation of the noise equivalent power value. The results show that the proposed method could be applied to increase the sensitivity of various commercial IR sensors in the THz range, requiring no modification of the internal structure and may be applied also to acoustics and plasmonics.

Fast evaluation of the array response matrix and its vector or matrix products play a central role in several applied electromagnetics and array processing applications. In this context, the Kronecker Array Transform (KAT) has been introduced by Ribeiro and Nascimento as an efficient factorization technique that can be applied when the elements of a planar array and the wavevectors exhibit separability. The computational savings leverage on the decomposition of the full array response matrix in the Kronecker product of two smaller array response matrices. In this contribution we extend and apply the generalized Kronecker product introduced by Fino and Algazi to the array response matrix decomposition problem. The resulting Generalized Kronecker Array Transform (GKAT) broadens the class of problems that can be addressed while achieving the same computational savings. The complexity of GKAT is compared with Non-Uniform Fast Fourier Transform (NUFFT), and optimal integration of the two techniques is elaborated.

In this paper, a highly efficient microstrip diplexer with low insertion loss, high selectivity, and high isolation is introduced. The proposed diplexer employed two compact size coupled squared open-loop resonator (SOLR) based band pass filters (BPFs). Firstly, a matching network is utilized to ensure that the two BPFs and the antenna load are properly matched. This is accomplished by connecting the two BPFs and the antenna with a conventional T-junction that acts as a combining circuit, resulting in good isolation between the up-link and down-link BPFs. As a second step, a defected ground structure (DGS) is used to improve the overall filter response in terms of insertion loss and isolation without affecting the diplexer selectivity. Based on this structure, the proposed diplexer has two resonance frequencies of 2.5 GHz and 2.8 GHz. The structure provides good insertion losses of about 1.6 and 1.3 dB for the two channels, respectively with fractional bandwidth of 2.8% at 2.5 GHz and 3.2% at 2.8 GHz. The measured isolation levels are 70 dB and 50 dB for 2.5 GHz and 2.8 GHz, respectively. The proposed diplexer is useful for several wireless communication applications such as WiMAX. The good agreements between simulated and measured results verified the practical validation of the proposed diplexer.

In order to improve the robustness of the fractional order sliding mode controller (FSMC) for permanent magnet synchronous motor (PMSM) sensorless control, a fractional order sliding mode controller based on T-S fuzzy inference algorithm (FFSMC) is proposed to observe the rotor speed and position information. Based on the mathematical model of PMSM and sliding mode controller, a fractional order sliding mode controller is designed, and its stability is proved. The T-S fuzzy inference algorithm is used to tune the reaching law parameters of the FSMC, so that the reaching law parameters are no longer fixed values, but change with the state of the system. The correctness of the proposed method is verified by MATLAB simulation software. The effectiveness of the simulation results is verified by building a PMSM sensorless control experimental platform. The results show that the PMSM sensorless control based on FFSMC achieves parameter self-tuning and improves the observation accuracy. And the robustness of the control system is enhanced.

An advanced 2D mode theory of plane electromagnetic wave diffraction by a transmission dielectric grating (rectangular relief or planar sinusoidal one) is considered. On the bases of this theory, a new model of diffraction of a spatially inhomogeneous light field (a Gaussian beam) by a transmission grating with arbitrary thickness is developed. It provides the opportunity to compute the transverse spatial structure of radiation diffraction orders and to estimate character of their distortions in comparison with the initial Gaussian beam structure. It is shown that such distortions appear under abrupt variations of intensity of all orders and can be caused by transformation of a certain diffraction order from the radiation regime of propagation into the waveguide regime and inversely (Wood's anomalies), and also it can be induced by a set of additional reflections on the boundaries of a thick substrate.

The numerous high-power devices and cables gathered around the subway vehicle will aggravate the deterioration of the electromagnetic environment, which may cause the train to fail to operate normally or threaten the health of passengers with a pacemaker or defibrillator. In order to study the distribution characteristics of low-frequency magnetic field of the subway in complex electromagnetic environment and the influence of various factors on human electromagnetic exposure, the magnetic flux density nephograms of the subway train with different vehicle body materials, with or without windows and with the shielding layer are calculated and analyzed. Specific energy absorption rate (SAR) values have been calculated in a standing voxel model from exposure to electromagnetic fields at 2.4 GHz, frequencies commonly used by Wi-Fi devices. The numerical results show that the average value of magnetic flux density in the stainless-steel carriage is less than that in the aluminum alloy carriage and the carbon fiber reinforce plastic (CFRP) carriage. Compared with the vehicle with windows, the average value of magnetic flux density in the vehicle without windows is less. The added shielding layer decreases the average value of magnetic flux density from 10.5 uT to 3 uT. The maximum value of magnetic flux density in the carriage under different factors is about 10 uT, which is far less than the magnetic flux density reference limit of 0.1 mT of the International Commission of Non-Ionizing Radiation Protection (ICNIRP) standard. Whenthe Wi-Fi device is closest to the human body, the highest Specific Absorption Ratio (SAR) value of human tissue is 0.00749 W/kg, which is far less than the electromagnetic exposure limit of 1.6 W/kg of IEEE standard.

A novel and efficient method to overcome the barriers of conventional diffraction limit using a specially designed metamaterial Split Ring Resonator (SRR) structure as an imaging sensor at microwave frequency is proposed. The topology of the proposed sensor is ingeniously designed to identify imaging objects having dimensions much less than the interacting wavelength λ. The split gap field region of the conventional SRR, used as the sensing region of the imaging sensor, is modified for enhancing the resolution capacity, by slightly raising the split region of the outer ring structure perpendicular to the plane of the resonator (Projected Split Ring Resonator - PSRR) which will reduce the area of the sensing region of the SRR probe considerably. The isolation of the structural parts of the SRR other than projected split region helps in using the localized evanescent field at the split region of the PSRR for imaging of minute objects having dimension ranges up to 0.0001λ by precisely choosing the split gap. The required projection height of the split region and the possible resolution limits of the PSRR sensor probe are evaluated by simulation. Experimental 2-dimensional sub-wavelength images obtained for various dielectric objects using a typical PSRR test probe having resolution capability up to 0.01λ are also presented.

We introduce and numerically investigate a high-quality resonant structure formed by a dielectric low-order diffraction grating combining materials with high refractive index contrast. The proposed structure is capable of supporting multiple plasmonic modes owing to hybridization effects, modes having the characteristic of exhibiting remarkable sensing response to the change of the environment refractive index yet limited figure of merit. To improve the figure of merit, the proposed architecture is modified by adding a layer of semiconductor gain medium, as it can compensate the internal losses. The result is an active sensor showing multi-modal lasing behaviour, with very low threshold and large mode spacing. It is found that the device shows switchable response upon modification of the pump amplitude or polarization, a very important feature when it comes to sensing devices. Finally, the achieved figure of merit is 3400 RIU^-1, one order of magnitude higher than the passive case and much higher than the theoretical limit for sensors based on Kretschmann configuration. Thus, the proposed architecture possesses great potentials as an optical sensor for bio-detection and environmental monitoring.

In this work, a radio frequency (RF) micro-electromechanical system (MEMS) based analog phase shifter is presented over 17-30 GHz. The proposed phase shifter is made using two back-to-back single-pole-seven-throw (SP7T) switches and connected through seven distributed MEMS transmission lines (DMTL). The SP7T switch is designed with lateral electrostatic actuation and demonstrates measured average return loss of > 11.3 dB, insertion loss of < 5.94 dB, and isolation of > 22 dB up to 30 GHz. Total area of the SP7T switch is only 0.89 mm² including bias lines and pads. The proposed wide-band phase shifter can be tuned at all the frequencies between 17 and 30 GHz. Phase shifter gives measured average insertion loss of < 6.94 dB, return loss of > 10 dB, and phase error of ~10 at 17 GHz to 30 GHz over 500 MHz bandwidth. All phase shifts can be tracked with a resolution of 22.50 based on predefined actuation voltages. Total area of the fabricated device is ~11.72 mm². In addition, switches and phase shifter work satisfactorily > 1 billion cycles with 0.1-1 W of RF power. The proposed phase shifter bank gives phase shifting performances at each frequency over 17-30 GHz with a constant resolution utilizing analog tuning, and it operates > 1 billion cycles of reliability with 1 W of RF power.

The tapered waveguide as a microwave plasma excitation structure is widely used in the industrial field. However, it needs high input microwave power to ignite and sustain plasma because its electric field is not sufficiently focused in the discharge area. In order to solve this problem, this paper proposes a novel microwave plasma source based on a ridged waveguide. The structure of the proposed microwave plasma source is optimized to focus the electric field in the discharge region by electromagnetic calculations before the plasma excitation. Then, the equivalent circuit model is used to analyze the impedance matching characteristics of the novel device after the plasma excitation. In order to validate this device, a microwave plasma system is built to measure the plasma exciting power and sustaining power in both air and argon at atmospheric pressure. The simulation and experiment are carried out in both tapered waveguide and the proposed device. Simulation results show the electric field of the ridged waveguide is 1.9 times of that of the tapered waveguide when the input power is 1500 W. Moreover, in the experiments, the exciting power and sustaining power of the air and argon plasma in the novel device are lower than those of the tapered waveguide at different gas flow rates.

A compact ultra-wideband Multiple-Input-Multiple Output (MIMO) orthogonal microstrip fed linear tapered slot antenna (LTSA) is planned for frequency notched applications. The projected MIMO antenna comprises of two indistinguishable linear tapered slot antennas excited by two orthogonal microstrip feeds. In this paper, double split-ring resonators (DSRRs) are suggested to develop the isolation between two linear tapered slot antenna elements. A quarter wavelength spur line is entrenched on the feeding part of the micro-strip antenna to attain the notch frequency. The L-shaped spur line adds to the notch frequency at 5.5 GHz targeted to dodge interference from 5-6 GHz WLAN band. The planned antenna is fabricated and labelled in terms of impedance and radiation parameter measurements, compliant with that of properties achieved from full wave simulation. The antenna has congruous gain and well-built radiation pattern. Radiation pattern portrayal confirms high gain in the end-fire direction.

The present paper introduces the analysis and design of a near field RFID tag for IoT in sub-six GHz 5G frequency band. The proposed radio frequency identification technique is based on the near field interaction between the RFID tag and a wideband antenna reader. This near field interaction adjusts the resonances of the wideband antenna according to the used RFID tag. In addition, the far field RCS of the RFID tag is also investigated to study the relation between the near field and the far field responses of the proposed RFID tag. The proposed RFID tag is characterized with adjustable six resonances based on concentric square rings printed on a dielectric slab. For manufacturing and experimental verification, the dielectric slab is assumed to be FR-4. However, the proposed structure can be generalized to other thin and flexible substrates like paper, plastic and textile.

This article reports the development and test of a radio-propagation measurement system based on an 8-bit software-defined radio. Tests are performed in an urban area at the frequency of 733 MHz and compared with numerical prediction from the Altair WinProp commercial suite. The system is portable (1.2 kg), low-cost, based on non-proprietary open-source tools and has the capability of tracking the GPS coordinates of the measured points. Frequency limit of the system is bounded by the software-defined radio in use, and the limit of this present case spans 24 MHz to 1700 MHz. The integrated system does not need user intervention after its initial setup can be operated autonomously.

In this paper, a dual-band impedance transforming power divider is investigated for all types of impedance environments at its ports, irrespective of the locations of the ports. The intuitive design approach utilizes conventional single-band Wilkinson Power Divider (WPD) architecture to provide the superior dual-band performance with arbitrary port impedances. The proposed power divider also accords a high degree of design flexibility with high frequency ratios (r) and impedance transformation ratios (k). The presented concept is evaluated and verified by design examples and measurements with a fabricated prototype. The agreement between the simulation and measurement results validates the working of the proposed architecture with arbitrary source and load port impedances at two arbitrary design frequencies.

In this paper, we apply the BBGF-KKR-MST (Broadband Green's function-KKR-Multiple Scattering Theory) to calculate Band Structures and Band Field Solutions in topological acoustics. A feature of BBGF is that the lattice Green's functions are broadband, and the transformations to cylindrical waves are calculated rapidly for many frequencies for speedy calculation of the determinant of the KKR equation. For the two bands of interest, only 5 cylindrical waves are sufficient so that the dimension of the eigenvalue matrix equation is only 5. The CPU time requirement, including setup and using MATLAB on a standard laptop, is 5 milliseconds for a band eigenvalue. Using the eigenvalue and the scattered field eigenvector, the field in the cell is calculated by higher order cylindrical waves. The exciting field of higher order cylindrical waves requires only 11 coefficients to represent the band field solutions in the cell. Comparisons are made with the results of the volume integral equation method and the commercial software COMSOL. The BBGF-KKR-MST method is significantly faster.

Unipolar induction has been a heavily discussed phenomenon in the realm of electrodynamics, with research and experiments proposing and supporting different ways to explain the observed effects. This paper presents a novel model to predict induced electromotive forces in a Faraday generator, based on direct interaction between conductor charges. It is compared with predictions that are usually obtained through considerations of Lorentz force, flux linking or flux cutting rules. A standard apparatus provides additional experimental measurements that show good agreement with the theory.