Vol. 92

A myriad of ultra-wideband (UWB) 180˚ hybrids have been reported that operate at frequencies below 20 GHz. However, parasitics from printed circuit board (PCB) transmission lines become significantly more problematic as the frequency is extended to mm-wave frequencies. Here, abroadside coupled transmission line hybrid is investigated for operation at 12-67 GHz. It is shown that a parasitic time delay for the odd mode exists at the junction between coupled and uncoupled transmission lines. A heterogeneous multi-layer PCB stack-up is leveraged to compensate for the junction parasitics over an ultra-wide bandwidth. Measurements have an insertion loss between 2 and 12 dB across the band, < 1.5 dB amplitude balance, < 10˚ phase balance, and > 19 dB isolation.

Nowadays compact terminal is one of the general requirements of modern wireless communication systems. The size of antenna limits further reduction of the structure size. To reduce size, a compact planar antenna based on Printed Circuit Board (PCB) is presented in this paper. This antenna has a new small-scale radiation coupling structure with a small hole and a matching element. This structure makes the ground structure of the circuit become an effective radiator through resonant coupling. This compact design avoids an independent big size radiator and the coupling structure over one quarter wavelength. Meanwhile, it can make the circuit have a good antenna matching effect at specific frequency by adjusting the lumped capacitance. Through the simulation and experiment, the design of antenna in 2.4 GHz ISM band is verified. The measurement results show that the antenna has 1.82 dBi gain and 151˚ beamwidth. It can be used in the compact wireless communication devices with advantages of low profile, adjustable frequency, and compact size.

In this paper, a dual-band dual-polarized magneto-electric (ME) dipole antenna with a dual-layer structure is proposed. The antenna consists of a dual-layer magneto-electric dipole, a Γ-shaped feeding line, and a rectangular box-shaped reflector. The dual-layer magneto-electric dipole is able to generate two resonant frequencies. Both simulated and measured results show that the antenna can obtain two wide impedance bandwidths of 47.5% (1.70-2.76 GHz) in lower frequency band and 30.2% (4.50-6.10 GHz) in higher frequency band with the reflection coefficients lower than -10 dB for both input ports. The isolation between ports is greater than 25 dB in the corresponding frequency band. The gains of the measured antenna are 8.5-9.7 dBi in the low frequency band and 7.5-8.5 dBi in the high frequency band, respectively.

In this paper, local meteorological data of one year have been used to calculate the surface atmospheric radio refractivity (N) and estimate the vertical refractivity gradient (dN₁) as well as the geoclimatic factor (K) in the lowest atmospheric layer above the ground surface in the station Kuujjuaq (Quebec, Canada). In this region, the climate is arctic, characterized by very long and very cold winters (on average the temperature is below -20˚C for almost 240 days per year). The precipitations are almost nonexistent, and the vegetation is scarce. Average daily, monthly, seasonal, and yearly variations of the N, dN₁, and K are estimated and analysed. The obtained values of these indices are compared to the corresponding values provided by the ITU. The results show that the more negative values of dN₁ lie in the summer season. This is mainly due to the important variations of the temperature and humidity during this season. However, the estimated values lie in the limits mostly corresponding to standard refraction.

This article describes a compact split ring monopole antenna loaded with a Hexagonal Split Ring Resonator (Hex-SRR) for Wireless Local Area Network (WLAN) and Radio frequency Identification (RFID) applications. The resonance frequency of the proposed antenna is obtained by making use of a split ring structure and a metamaterial element Hex-SRR. The prototype antenna is printed on an FR-4 substrate having a dielectric constant (ε_r) of 4.4 with dimensions of 21×21×1.6 mm³. The split in the ring radiating element is used to achieve good impedance matching, and the Hex-SRR creates a new resonance frequency of 5.8 GHz. This paper includes equivalent circuit investigation, operating mechanism, and band characteristics of Hex-SRR as well as negative permeability details. The fabricated antenna provides an impedance bandwidth of 1180 MHz (5.23-6.41 GHz), which is suitable for WLAN and RFID applications. Good similarity is inferred between the simulated and measured results of the proposed antenna.

We present a three-dimensional finite element (FEM) field-flux eigenmode formulation, able to provide accurate modeling of the propagation characteristics of periodic structures featuring graphene. The proposed formulation leads to a linear eigenmode problem, where the effective refractive index is an unknown eigenvalue; the electric field intensity and magnetic flux density are the state variables; and graphene's contribution is efficiently incorporated via a finite conductivity boundary condition. The FEM formulation is spurious-mode free and capable of providing accurate dispersion diagrams and field distributions for arbitrary propagation directions, as opposed toother analytical or numerical approaches, while also efficiently dealing with graphene's dispersive nature. The novelty of the presented approximation is substantiated by computational results for structures incorporating graphene of random periodicity, both within passbands and bandgap frequencies.

Drawing on the ideas of stator permanent magnet motors, hybrid planetary gears are integrated into permanent magnet motors using hybrid excitation on the stator side, and a new type of stator-hybrid magnetic planetary gear motor for steering systems is proposed. The magnetic gear motor overcomes the shortcomings of the existing magnetic gear structure and performance, and has the advantages of high reliability, strong torque transmission capacity and large transmission ratio. At the same time, it can adjust the levitation force and power in real time as the working conditions change, improving motor efficiency. This paper focuses on the topology and working principle of the stator-excited planetary magnetic gear motor. According to the finite element analysis, the magnetic field distribution is obtained, and the rationality of the magnetic field is analyzed. Theoretical analysis and experimental results show that the magnetic circuit of the stator-hybrid excitation planetary gear motor is correct, and the torque can meet the design requirements. This method provides reference and application value for the development of high performance and low cost permanent magnet planetary gear motors.

The complete analytical formulation of periodic structures using metamaterials formed with split ring resonators (SRRs) is developed. The periodic structure modeling is based on coplanar waveguide transmission line method and network parameters. The full effect of mutual inductances in the array design is integrated for the first time using curve fitting techniques with electromagnetic simulator. The simplified equivalent circuit including the effect of mutual inductance is presented. The proposed formulation is then used to design a unit cell composed of two SRRs of the sensor array. The analytical method is then verified with simulation results. The prototype of the unit cell has then been manufactured and measured at different frequencies. The analytical, simulation, and measurement results are compared, and agreement has been confirmed.

Near-field magnetic measurement is a simple but effective way of researching the magical electromagnetic properties of metamaterials. However, till now, the experiments in the field of metamaterials have involved only far-field macroscopic and near-field electric measurements because of the difficulty in isolating interference from electric fields. In this research, we design and fabricate a near-field magnetic probe with about an one-tenth wavelength size and 20 dB E-field rejection ratio, which can be combined with a parallel double-plate device integrating a system for measuring anisotropic vector magnetic field. As a verification measurement of plane waves and cylindrical waves, it got the clear vector field distribution characteristics and good anisotropy. Next we used the dipole to measure the typical metal split ring structure of the metamaterial. The measurement of the distribution of magnetic fields contributes to revealing the interaction mechanism between electromagnetic waves and metamaterials as well as the relationship between microscopic structural elements and macroscopic electromagnetic properties.

Microwave technology has been widely used in rubber industry. In order to solve the problem of uneven temperature distribution, a novel control method of adaptive multi-dimensional Taylor network combined with Cuckoo Search is proposed in this paper. The adaptive multi-dimensional Taylor network control method is used to obtain the suitable output powers and phase difference under unknown system parameters. Cuckoo Search algorithm is utilized to optimize the whole situation and find the best fit input variables at sampling points. To verify the proposed control strategy, the dielectric permittivity of nitrile butadiene rubber composites is measured, and the control process is simulated based on measured values. The simulation results show that the proposed method can well control the temperature rising process with little difference between the average temperature and reference trajectory.

Spatial transform techniques like transformation optics and conformal mapping have arisen as the dominant techniques for designing metamaterial devices. However, these techniques only produce the electrical permittivity and permeability as a function of position. The manner in which these functions are converted into physical metamaterial lattices remains elusive, except in some simple or canonical configurations. Metamaterial lattices designed by spatial transforms are composed of elements of different sizes, orientations, and designs. The elements must be distributed and oriented in a manner that makes the final lattice smooth, continuous, have uniform density, be free of unintentional defects, and have minimal distortions to the elements. Any of these would weaken or destroy the electromagnetic properties of the lattice. This paper describes a general purpose method to generate such arbitrary metamaterial lattices. Inputs to the algorithm are the permittivity and permeability functions as well as the baseline metamaterials that can provide the necessary permittivity and permeability values. In prior research, we reported a simple finite-difference technique for calculating the permittivity and permeability functions for arbitrary shaped devices using transformation optics. The present work is illustrated by generating an electromagnetic cloak of arbitrary shape that was designed using the previously reported technique. The final metamaterial cloak is simulated using the finite-difference time-domain method and performance compared to other cloaks reported in the literature.

In this paper, a novel heterogeneous swastika structured hexagonal photonic crystal ring resonator for the realization of universal logic gates is designed using two dimensional photonic crystals. The proposed structure has square lattice of 16 × 16 hexagon-shaped chalcogenide glass rods embedded in an air substrate with a refractive index of 3.1. The choice of chalcogenide in the realization of optical logic gates benefits from wide optical windows in the mid-infrared region. Through plane wave expansion method, the contrast ratio for the proposed structures, namely, NAND, NOR, EX-OR, and EX-NOR gates is 22.6 dB, 17.20 dB, 18.3 dB, and 12.78 dB, respectively. Moreover, the footprint of the proposed structure is 9.24 µm × 9.24 µm.

The novel design of an ultra-wideband calorimeter for energy measurement of high power microwave pulses of nanosecond duration is proposed in this paper. The main idea is the use of a circular waveguide with losses in the wall and metal cone insertion at the axis to increase attenuation constant in the waveguide. The efficiency of the concept was proved with the numeric simulation and optimization of the calorimeter design with ANSYS HFSS software for frequencies from 8 to 38 GHz. The operating modes are supposed to be symmetric TM_0n ones. Ethanol was chosen as an absorbing medium. It is parted from the vacuum volume by a plastic tube. The frequency dependencies of ethanol's relative permittivity and loss tangent were taken into account in the simulation model. The reflection coefficient for TM₀₁ mode is below -20 dB at the lowest frequency of 8 GHz and well below the level of -25 dB from 10 to 38 GHz. The reflection coefficients for higher order modes remain below -30 dB until the operating frequency is close to the cut-off frequency for a particular mode. The maximum accepted power level is of hundreds of megawatts for pulses of a nanoseconds duration. The effect of waveguide modes mixture at the input of the calorimeter on the maximum accepted power level was considered. This level may differ by 4 times between specific modes mixtures. Therefore, the transition from a particular microwave source to the calorimeter input should be carefully optimized.

Nowadays, the key to design a reliable communication system is to acquire channel characteristics and improve channel capacity. In the transmission of high-speed data, the unshielded transmission channel used in power line communication has interference factors such as noise, attenuation, reflection, radiation, and time-varying. A three-wire MIMO-PLC channel transfer function priori model has been established based on the theory of MTL in this paper, which is necessary for band pre-selection, power setting, and dynamic range design in a high-speed MIMO-PLC set to improve the unshielded transmission channel capacity with the effect of noise, attenuation, reaction, radiation, and time-varying factors. The simulation results with the model parameters of geometric sizes, material, surrounding medium, and lengths of the power line network agree well with the measurement ones in the frequency band of 1-200 MHz. The research results of this paper have guiding significance for the band pre-selection, power setting, and dynamic range design of broadband MIMO-PLC.

Human intention recognition is important for any interaction between the user and the exoskeleton. This study proposes a novel approach, based on a contactless sensory system, using linear Hall effect sensors to recognize human intentions. This contactless sensory system consists of four Hall effect sensors mounted on the exoskeleton, whilst a ring-shaped permanent magnet with diametrical magnetization consisting of two semi-rings is worn on the user's forearm. The model of the magnetic field created by the permanent magnet is also developed. Based on the developed magnetic field model and by interpreting the signals from the Hall effect sensory system received while the user's elbow and forearm move, the intention identification algorithm is derived. A lightweight elbow and forearm assistive exoskeleton is developed. The proposed approach for human intention recognition is used to assist in controlling the exoskeleton, following the wearer's intended motions. By implementing this contactless sensory system, wearers can use the exoskeleton easily and can move their forearm comfortably, while the human intention motion is recognized and used to control the exoskeleton. Moreover, achieved signals are unaffected by skin perspiration and muscle fatigue. As the sensory system is mounted on the exoskeleton, there is only indirect contact between the user's body and the sensors, leading to improved comfort. Finally, the system does not require expert knowledge to place the sensors on the body of the user. This approach can be extended to detect human intentions for the control of exoskeletons with more degrees of freedom.

This paper presents a compact single feed circularly polarized (CP) antenna along with a frequency selective surface (FSS) that acts as a partially reflective surface over the patch. Patch is loaded with four diagonally asymmetric complementary split ring resonators (CSRRs) in order to achieve circular polarization. In this paper a novel design of reflective type FSS layer is presented at 2.4 GHz. The size of FSS unit cell is approximately 0.132λ₀ × 0.132λ₀, and it is placed at a distance of 0.146λ₀ from the patch. Simulated impedance bandwidth of the antenna for S₁₁ < -10 dB is from 2.385 GHz to 2.506 GHz (121 MHz or 4.95%) which covers the entire IEEE 802.11 WLAN band (2.4 GHz-2.484 GHz). Position of the four CSRRs on the patch and the height of FSS screen are determined through parametric studies, and the detailed analyses in terms of reflection coefficient, axial ratio, and gain variation are also presented. Gain of the antenna is 3.02 dBic at the operating frequency 2.45 GHz. Measured results are in good agreement with the simulated ones.

In this article, the Modal Expansion Theory (MET) is applied to 3-D metamaterial waveguides. The equivalent surface impedances of the metamaterial are computed thanks to an open software: GetDP, based on a 3-D Finite-Element-Method (FEM). This program is called during the MET algorithm, which allows considering the frequency and incidence angle dependency of the surface impedances of the metamaterial to compute the dispersion diagrams and the field cartography. To validate the dispersion diagrams obtained with this technique, another FEM commercial software (HFSS) is used as a reference.

Concentric circular slots coupled hemispherical dielectric resonator antenna fed by a modified microstrip line for circular polarization is investigated. By adjusting the position of the hemispherical dielectric resonator antenna and the slot properly, the resonance of the slot and the antenna is merged to obtain wider axial ratio bandwidth. Parametric studies have been done on the effect of changing the DRA position on impedance band and axial ratio band. The circular polarization achieved by the antenna offers a very good 10 dB impedance bandwidth of 27.379% and a 3 dB axial ratio bandwidth of 640 MHz. The maximum gain in the operational band is 7.3 dBi. The antenna is suitable for Wi-Max applications.

This paper analyzes the high-frequency energy distribution of a paraboloid reflector in the presence of a uniform plasma layer. The curved surface of the paraboloid reflector is thought to be coated with a uniform plasma layer. The geometrical optics technique shows a singularity at the focal point of the paraboloid reflector. The singularity is removed with the help of Maslov's method, which also let us derive the integral equations that give the high-frequency energy distribution at the focal point. The analytical integral is solved numerically using a computational technique, and the effects of plasma frequency, collisional frequency, operating frequency, and multiple reflections on energy distribution at the focal point are observed. Under the special conditions our analytical and numerical results are obtained which align with the published literature.

The Lienard-Wiechert potentials show explicitly that charge acceleration, i.e., a change in charge velocity, causes radiation of an electromagnetic field. The goal of this discussion is to explore the rate of energy loss due to radiation from current and charge flowing on a circular loop as a function of the loop's curvature and wire radius. The results presented are obtained using a thin-wire, time-domain (TWTD) computer model for Gaussian-pulse excitation. Some results for a straight wire are also presented for comparison. Analytical estimates for the curvature and wire-radius effects are developed from best-fits expressions to the computed results.