In this paper, a design of dual band 10 × 10 antenna array for 5G Massive Multi-Input Multi-Output (MIMO) applications in the mobile phone is presented. The designed array is proposed to cover the sub-6 GHz bands (LTE bands 42/43 and LTE band 46). To realize MIMO operation in these three LTE bands, ten ring loop antenna elements are integrated into a limited space cell phone circuit board. Due to the implementation of spatial diversity techniques on the antenna elements, better isolation can be achieved. The proposed array was simulated, fabricated and measured. It achieved good MIMO performances, such as ergodic channel capacities higher than 27.1 bps/Hz and 57.6 bps/Hz for LTE bands 42/43 and LTE band 46 respectively. Also, the achieved Envelope Correlation Coefficient (ECC) is lower than 0.006. Moreover, it exhibited good isolation below -26 dB. The effects of user's hand phantom on the proposed array performance are also studied in two scenarios: Single Hand Mode (SHM) and Dual Hands Mode (DHM). The simulated results indicate that the proposed MIMO array can still achieve good MIMO performances in the presence of DHM and SHM. The Specific Absorption Rate (SAR) are also presented.

We here present a bivariate Chebyshev series method for the approximation of the experimental frequency and temperature dependent dielectric functions of materials. Within the framework of this method, the dielectric properties are modeled as a low-degree polynomial of the temperature variable (T), the coefficients of which have a frequency (variable f) dependency. This model is then rephrased in terms of the temperature coefficients which are given here as the rational functions of frequency. The principal merits of this method are that it produces a near-best polynomial approximation to the target function, rapidly improves with the order of approximation, and is easy to compute. The favorable features of our approach are demonstrated by considering the experimental wideband Cole-Cole models of animal tissues with the temperature-dependent parameters. The numerical results show the inferiority of the commonly used power-of-f representation of the polynomials concerned due to large rounding errors when the frequency range is large. This problem is ameliorated by expressing the appertaining coefficients as polynomials in the transformed frequency variable x(f) in the Chebyshev basis. Areas of application of the results of this article include the modeling of human exposure to radiofrequency fields, development of treatment and diagnostic procedures, and food processing technologies.

A self-quadruplexing antenna based on substrate integrated waveguide (SIW) is presented. A slot is engraved on its top surface of the SIW cavity, which generates four different resonant frequencies (around 6.54, 7.64, 8.30, and 9.60 GHz) when it is excited by four 50 Ω microstrip feed lines. Also, each resonant frequency can be controlled independently. Due to a quarter mode (QM) cavity, the antenna size becomes compact. The measured results show that the isolation between any two ports ismore than 32 dB, and the estimated gain is more than 7.8 dBi at the operating frequencies. The proposed design is simple to fabricate, compact, and easy to integrate with the planner circuits.

This paper presents an analysis of microstrip patch antennas with different dielectric/magnetic substrate profiles in an attempt to obtain operating frequency reduction. Initially, different ridge shapes in the substrate were examined. An in-depth investigation of the ridge shape and its dimensions on the antenna performance has been carried out. Subsequently an antenna with a magnetic-slab loaded in the prime magnetic-field region beneath the patch is proposed. The new magnetic loaded antenna design is aimed to reduce the resonant frequency of a conventional patch and reduce the profile of an earlier design with a substrate ridge. Various magnetic materials have been embedded within the original dielectric substrate of the patch antenna. Measured results validated the hypothesis that this frequency can be reduced by placing magnetic materials at the centre of the patch. The achieved gain is expected to be further enhanced by using forthcoming magnetic materials with improved performance.

A backward wave oscillator (BWO) operating at the high-order mode (HOM) with multiple inclined rectangular electron beams (IRBs) is presented in this article. The BWO operating at the HOM with multiple IRBs (HOM IRB BWO) is driven by multiple IRBs. Compared with typical BWOs, the slow wave structure of the HOM IRB BWO is an overmoded metal-grating rectangular waveguide (OGRWG). The mode competition of the slow-wave device operating at the HOM is analyzed according to the ohmic losses of different modes of the OGRWG slow wave structure and multiple beams exciting. The analysis is verified by simulation. Two kinds of HOM-fundamental mode converters (MCs) are designed for converting the HOM generated by the HOM IRB BWO into the fundamental mode. The beam-wave interaction of the HOM IRB BWOs with the HOM-fundamental MC is studied. The results show that the mode competition does not occur; frequency spectrums of output signals are pure; the HOM is converted into the fundamental mode effectively.

An investigation on using eco-friendly natural materials like coconut pith, rubber and charcoal powder for developing radio wave absorbers has been reported in this paper. Two absorbers named CoR (Combination of Coconut pith powder and natural Rubber latex) and CoRC (Combination of Coconut pith powder, natural Rubber latex and Charcoal powder) are made through proper mixing and drying. The absorptivity of these two absorbers (CoR and CoRC) is compared with the industrial standard polyurethane based absorber. The waveguide method is employed to measure the absorptivity of these absorbers in 3 different frequency bands. Band 1 (1.7-2.6 GHz) includes the mobile communication frequencies of 1.8 GHz and 2.4 GHz. Band 2 (4.9-7.05 GHz) is intended for sub 6 GHz band of 5G as well as WLAN frequencies while band 3 (8.2-12 GHz) is for higher frequencies of radar operation. The exact values of lower and upper frequencies of bands are determined by the physical dimensions of waveguides used. The absorption capability of the absorbers is found to increase as the frequency of operation increases. The CoR absorber has almost 63% average absorptivity in band 3, 56% in band 2 and 21% in band 1. The CoRC absorber has an average of 74% absorptivity in band 3, 63% in band 2 and 24% in band 1.

A low-profile compact uni-planar slot antenna design of size 26 mm × 26 mm is proposed, assisted with a metallic bottom reflector at a height of λ/6 (λ is the lowest CP frequency). The dual-band dual-polarization is observed at 6.2 GHz and 9.3 GHz, and polarization sense (LHCP and RHCP) is dynamically switched by introducing a pair of RF p-i-n diodes mounted at the confluence of right-slot (RS) and left-slot (LS). The metallic reflector of size 60 mm × 60 mm helps to improve overall impedance matching, enhance antenna gain and asserts uni-directional dual-polarized radiation with good back-lobe suppression. The proposed antenna operates at dual bands (5.46-6.76 GHz) with 21.27% IBW and (8.18-10.48 GHz) with 24.65% IBW for S₁₁ < -10 dB. The antenna gain reaches (7.82-8.75 dBi) for D1-OFF, D2-ON state with (9.2%, 15.63%) axial bandwidths and (6.42-7.0 dBi) for D1-ON, D2-OFF state with (7.53%, 16.04%) axial bandwidths with radiation efficiency ranging (75-87%). A prototype antenna is fabricated and measured, which shows good agreements with simulated performances and can be used for sub-6 GHz in 5G applications and X-band radar systems.

This letter shows a compact planar microstrip crossover. The crossover design employs a microstrip to coplanar waveguide transition. The crossover is fabricated on a low cost and readily available FR-4 substrate, and simulation and measurement responses in the low frequency band have been shown. The number of GND vias forming a quasi-coaxial section that confined the electric field around the signal via was increased to improve impedance matching. The core size of the circuit is as compact as 20 mm × 10 mm even in the low frequency band. The crossover operates in the low frequency band with insertion loss of less than 1 dB, return loss of more than 10 dB, and isolation of more than 15 dB.

A frequency reconfigurable antenna with conical radiation pattern is presented. The antenna is mainly composed of a suspended circular patch, eight shorting posts, and a ground plane. The circular patch is loaded with two concentric annular slots, and four varactors are placed across the outer annular slot to vary the resonant frequency of the antenna. Simulated results show that the resonant frequency can be tuned from 3.25 to 5.7 GHz as the capacitance of the varactors is varied from 0.2 to 12 pF, and conical radiation patterns are obtained when the antenna is operated at each resonant frequency. In the simulation, the reversed-bias circuit of the varactor is also included, and it is found that a bias tee or an inductor is not necessary for the proposed reconfigurable antenna. Experiments are also realized using two different varactors, and the measured results indicate that the peak gains of the conical radiation patterns occur around θ = ±40˚, and they are about 4.5 ± 1.5 dBi when the constructed prototypes are operated in the frequency range from 3.1 to 5.7 GHz.

Reflective interference caused by impedance discontinuities in the interconnect is a serious impediment to high speed serial link designs. The reflections can be addressed either through expensive equalization circuits or through interconnect redesign. Here a new technique for determining the most significant places to make changes in an interconnect design is presented. Through linearizing the S-parameter cascading process three unique reflection budgets are created based on 1) frequency domain insertion loss deviation, 2) time domain peak distortion analysis and 3) time domain reflectometry. Example analysis of a 25.8 Gb/s NRZ system identifies the connectors as the primary contributors to reflective interference and estimates that the interactions with the rest of the interconnect with the connector impedance discontinuities reduces the system eye height by 84 mV.

Uncertainty quantification and variability analysis are two domains of interest when looking at the efficiency of HPEM sources. Vircator is known to be a low efficiency high power microwave source subject to several generally volatile phenomena such as plasma expansion and shot-to-shot variability. In this study, a computationally low cost framework combining the Extreme Value Theory (EVT) and the Generalised Design of Experiments is proposed in order to study the peak power distribution of a Vircator obtained with a surrogate model. Following the pre-screening of random variables, the optimised parameters are introduced in 2.5D and 3D simulation tools, namely XOOPIC and CST-PS. It has been confirmed that the peak power output can reach a 40% increase. This shows that the EVT proves to be successful in classifying and quantifying random variables to influence the distribution tails.

A compact ultra-wideband antenna is presented for detecting malignant cells in the breast. The dimension of the proposed circular resonator-based antenna is 20 mm x 30 mm x 1.6 mm. The antenna sensor operates within the 3.1 GHz to 6.8 GHz (105.71%) range with peak gain 4.8 dB, radiation efficiency 89.2%, and an omnidirectional radiation pattern. Three types of breast phantoms (i.e., phantom without tumor, a phantom with a single tumor, and phantom with two tumors) arealso fabricated. The electrical properties of the malignant cells differ from non-malignant breast cells. S-parameters have been measured with phantom, then with the help of Principal Component Analysis (PCA), and normal and malignant breast phantoms are identified. Further, the tumor's locations in the breast phantom are find out by using the specific absorption rate (SAR) values.

In this paper, a UWB monopole antenna with triple band-notch characteristics using single TBMV-EBG (Triple band multi-via electromagnetic bandgap) unit cell is proposed and demonstrated. The antenna with a fork-type radiating patch with TBMV-EBG is simulated using Ansys HFSS. Measurement results show triple band-notches at 3.39, 5.78, and 8.60 GHz, respectively, which are in good agreement with simulation results. The proposed antenna has bi-directional pattern in E-plane and omnidirectional pattern in H-plane. Moreover, tunable characteristics of the proposed antenna using a single varactor diode are also presented. By changing the capacitance of varactor, the band-notched antenna is effectively tuned from 2.69-3.46, 5.71-7.84, and 8.40-8.50 GHz. The same antenna structure can be operated at different band notching modes depending upon the varactor's capacitance. Therefore, the proposed UWB antenna will prove to be a promising candidate wherein multi-band rejections using single TBMV-EBG unit cell and reconfiguration using one varactor diode are desirable.

In this work we present near-field image transmission and error vector magnitude measurement in rich scattering environment in metal enclosure. We check the effect of loading metal enclosure on the performance of SDR based near-field communication link. We focus on the key communication receiver parameters to observe the effect of near-field link in presence of rich-scattering and in presence of loading with RF absorber cones. The near-field performance is measured by transmitting wideband OFDM-modulated packets containing image information. Our finding suggests that the performance of OFDM based wideband near-field communication improves when metal enclosure is loaded with RF absorbers. Near-field EVM improves when the enclosure is loaded with RF absorber cones. Loading of the metal enclosure has the effect of increased coherence bandwidth. Frequency selectivity was observed in an empty enclosure which suggests coherence bandwidth less than the signal bandwidth.

The direct control for the bearingless permanent magnet synchronous motor (BPMSM) has problems of large ripples of flux linkage, torque, and suspension force due to sampling time delay. To solve above problems, a predictive direct control method is proposed based on the traditional direct control by adding prediction model. Firstly, the generation principle of radial suspension forces of the BPMSM is introduced. Secondly, the models of the predictive direct control method are given based on the traditional direct control, and the time-delay compensation model is deduced. Thirdly, the predictive direct control system is constructed, and the simulations are carried out. Finally, the proposed control strategy is applied to a prototype, and the related experimental results are given and analyzed. The results of the simulations and experiments show that compared with the traditional direct control of the BPMSM, the predictive direct control strategy can effectively reduce the ripples of flux linkage, torque, and suspension forces, and improve the static and dynamic performance of the BPMSM.

This paper develops a circuit theory on bandpass negative group delay (NGD) topology. The NGD active lumped circuit uses a low noise amplifier (LNA). An S-parameter model is formulated. Unfamiliar, NGD function analysis is introduced by analytically defining the NGD value, bandwidth, and central frequency in function of the topology parameters. The synthesis formulas enabling the calculation of cell parameters as a function of the targeted bandpass function specifications. To validate the circuit theory, an NGD proof of concept (PoC) is designed, simulated and tested. As expected, simulations and measurements are in good agreement. Calculated model, simulated and measured results showing NGD level of about -10 ns around the centre frequency 0.5 GHz over the bandwidth 50 MHz validate are obtained.

A new numerical method is proposed for uncertainty quantification in the two-dimensional finite-difference frequency-domain (FDFD) method. The method is based on an intrusive polynomial chaos expansion (PCE) of the Helmholtz equation in terms of the material properties. The resulting PCE-FDFD method is validated against Monte-Carlo simulations for an electromagnetic scattering problem at 1.0 GHz. Good agreement is found between the statistics of the electric fields computed using the proposed method and the Monte-Carlo results, with a factor 15-120 reduction in the computational costs. The PCE-FDFD method is also applied to estimate the material properties from exterior measurements by formulating an objective function and applying constrained optimisation techniques. A maximum 1.7% error in the material properties was observed for a test geometry with six unknowns and 20 sample points.

This paper proposes a method to recover vibration energy from a semi-active suspension system which is composed by a magneto rheological damper in parallel with a power regeneration mechanism. Central to the concept is a parity-time-symmetric (PT symmetric) circuit that is capable of providing high efficiency transmission of power and minimizing electromagnetic damping force of the power regeneration mechanism. Simulation results are presented to demonstrate the electromagnetic damping force of the power regeneration mechanism having little impact on suspension system and verify the possibility of energy recovery. The proposed control strategy pays close attention to inertial force of the power regeneration mechanism which produces indicator diagram hysteresis. To evaluate the performance brought about by the proposed method, the semi-active suspension utilizing the PT symmetric circuit is compared to the load resistance circuit. And the semi-active suspension system is implemented on a quarter car test bench to demonstrate its feasibility on a typical sine road surface.

Dynamic Wireless Power Transmission has attracted attention in the research area due to its safety, convenience, and automation. However, the major limitation in achieving this vision is its working distance. In this paper, the metamaterial (MM) based transmitter WPT with zero permeability is presented and compared with an inductive WPT system. The comparative simulations and experimental investigations validate the effectiveness of the proposed design. The system efficiencies are determined at the distances of 8 cm, 11 cm, and 16 cm between the transmitter and receiver (SAE J2954) with an operating frequency of 20 kHz. The power transfer efficiency (PTE) of the WPT system using an inductive transmitter and the WPT system using an MM-based transmitter is shown as 85/87%, 65/70%, 45/65%, respectively. The PTE of the MM-based transmitter is 64% higher than an inductive transmitter at a 16 cm distance. The robot without a battery moves dynamically along the track with the MM-based transmitter underneath. The results show that the power transfer efficiency of the MM-based transmitter is considerably higher than that of the inductive transmitter.

A low-loss electronic beam steering model is presented in this paper based on tightly-coupled dipole array topology for satellite communications applications for K through Ka-band (18-40) GHz. The array is low-profile having < 3.4 mm height and printed on an affordable single-layered PCB. As proof-of-concept, a 4 × 4-element, single polarized array is fabricated and measured showing (18-40) GHz (VSWR < 2) continual band coverage. A compact, low-loss electronic beam steering architecture for moderate bandwidth arrays is also utilized for beam steering. A 2-bits tunable phase shifter, spanning over (18-30) GHz with IL < 2.5 dB, is developed using micro-electro mechanical systems (MEMS) technology. The phase shifter is integrated at the array elements resulting in reduced size, cost, and complexity of the feeding network. A full-wave simulation of the 4 × Infinite array with the integrated MEMS phase shifter is conducted to prove the concept.