Vol. 94

In this manuscript, a high-performance beam-steerable phased array antenna is introduced for fifth-generation (5G) mobile handsets. The configuration of the design is arranged by employing eight dielectric-insensitive L-ring/slot-loop radiators in a linear form on the top edge of the handset mainboard. The beam-steerable array design exhibits high radiation performances even though it is implemented on a lossy FR-4 material. The proposed design exhibits an impedance bandwidth of 18-20 GHz with the center frequency of 19 GHz. It provides satisfactory characteristics such as wide beam-steering, high gain and efficiency characteristics indicating its promising potential for beam-steerable 5G smartphones. The characteristics of the antenna array are insensitive for different types of dielectrics. Furthermore, the designed antenna array offers quite good radiation behavior in the presence of hand phantom.

The present article shows the design, implementation, and measurement of a compact contactless electronic system for sensing small volumes of liquids. The system is based on two elements: an electronic reader and a passive sensor. The proposed sensor consists of a printed monopole antenna loaded with two Split-Ring Resonators. This results in a fully-passive and single-layer low-cost design. To allow the sensing of small volumes of liquids, a 1-mm-thick adhesive Kapton layer was attached on the top layer of the sensor, and two drop tanks were added to the structure. On the other hand, the reader was designed following a layered approach, which allows us to develop compact and low-cost electronic sensor readers for the Internet of Things. The resulting reader contains a Radio-Frequency interface for the generation of detection of signals, a minicomputer, and the radiating interface. This interface includes a patch antenna that allows us to interrogate the contactless sensor within a 1-cm range. The whole system was manufactured and tested. The total dimensions of the reader are 15 cm × 15 cm, and its weight is below 1 kg. These imply a dramatic form factor and weight reductions with respect to previous readers. Moreover, the manufactured system was used to measure the dielectric permittivity of different liquid drops. Results show that only 4 ml of liquid were needed to determine the dielectric permittivity with a 0.27% error. This volume means a 98.4% reduction compared to submersible sensors which can be found in the literature.

This paper presents Global Navigation Satellite System (GNSS) F-type and Bluetooth (BT) L-shaped antennas printed on flexible low loss substrate materials for smartwatch applications. The proposed printed antennas were designed along with the wristband of a smartwatch device with the main purpose of improving their electrical performance by using a new low loss polymer material and locating the antenna on the wrist strap. The antenna performances were simulated using CST Microwave Studio, and the prototypes were measured in a Satimo StarLab anechoic chamber. Silver printing and injection molding technologies were successfully utilized for fabricating new SEBS materials (styrene-ethylene-butylene-styrene) in wearable devices. The SEBS materials improved the radiation efficiency of the antennas by 1.6 dB for the GNSS and 2.2 dB for the BT over the previously used TPU (thermoplastic polyurethane) materials. The overmolded printed and hybrid integrated discrete antennas produced added-value for electronics fabrication thanks to its flexible and seamless integration technique. In addition, it is a low-cost mass manufacturing method. The research opens new perspectives for product definitions with a flexible, low loss material that enables better antenna performance.

In this paper, we design and fabricate a side lobe comb-line fed microstrip antenna array at the frequency of 77 GHz. This antenna can be used in car and also in peripheral protection radars. To design the antenna, a radiating microstrip element on a simple sublayer is first designed and optimized in order to have desirable specification at 77 GHz. Secondly, a one-dimensional array is formed using a row of microstrip antenna array with 32 serried elements. Finally, a two-dimensional antenna array with 16 rows is fabricated and subsequently fed with a waveguide to complete the antenna design.

This paper presents a novel compact multilayer meander strip line step-via electromagnetic band-gap (MLSV-EBG) structure with the application of mutual coupling reduction in a multilayer multiple input multiple output (MIMO) antenna. The proposed EBG-cell has been developed by using multilayer, novel meander strip line, and step-via concept. To analyse the proposed EBG a parallel LC model method is used. In the proposed MLSV-EBG structure, due to step-via concept, current path length increases, and compactness is achieved per unit cell. Parametric study is also presented. MLSV-EBG structure unit cell is simulated using ANSYS high frequency structure simulator (HFSS), and 5X5 cells are printed on an FR4 substrate for band-gap measurements. Simulated and measured results prove that compared with three-layer central located via EBG (CLV-EBG) and edge located via EBG (ELV-EBG), size reductions of 47.01% and 43.01% have been achieved, respectively, which shows that step via concept gives the significant size reduction per unit multilayer EBG cell. The application of proposed MLSV-EBG for the reduction of mutual coupling between two multilayer MIMO antennas is also demonstrated. The key contribution of the presented work is that the proposed compact multi-layer EBG structure is useful in a multi-layer environment at a lower frequency.

Estimation of soil moisture using Synthetic Aperture Radar (SAR) backscatter values, over agricultural area, is still difficult. SAR backscatter is sensitive to the surface properties like roughness, crop cover, and soil type, along with its strong sensitivity to the soil moisture. Hence, to develop a methodology for agricultural area soil moisture estimation using SAR, it is necessary to incorporate the effects of crop cover and soil texture in the soil moisture retrieval model. A field experiment was conducted by the authors and used along with Sentinel 1A SAR data to estimate the soil moisture in the paddy agricultural fields. Generally, water used for irrigation in the study region was obtained from ground water. As in the hot climate conditions ground water level would be reduced, and the water for irrigation must be supplied optimally. Hence, available soil moisture in the field was estimated from SAR data on the day of satellite passing the crop fields and utilized for deciding the amount of water to be supplied. The soil moisture values of soil samples that are collected from the agricultural field are calculated with the laboratory experiments. A soil moisture retrieval model is derived and proposed in this paper after a comparative analysis of experimental soil moisture values and satellite values. The feasibility of above model for paddy agricultural fields is validated using the field measurements.

This paper presents the design of flexible parasitic element patch (FPEP) antenna with defects on ground plane at ISM band for biomedical application. The antenna resonates at 2.46 GHz frequency with reflection coefficient of -16.8 GHz in free space and at 2.45 GHz frequency when being placed on cotton and the single layer skin tissue of human body. The proposed parasitic element patch antenna is used to measure the body temperature, and the specific absorption rate (SAR) of the proposed antennas is 1.0 W/kg. The measurement data with respect to reflection coefficient, and radiation pattern are presented.

With a constantly increasing number of cars equipped with 77 GHz automotive radar, the performance degrading effects of crosstalk are becoming a rising threat to radar-enabled automated driving functions. Since interference is sensitive to slight changes of temporal and spatial conditions of the scenario, meaningful measurements are hard to conduct which is why simulations are an important supplement. In this paper, a simulation model is introduced that estimates the distribution of the reduction of the detection range of automotive radars due to multiple interferers focusing on stochastic temporal conditions. The underlying system model calculates the direction- and timing-dependent influence of one single interferer on the detection range of the host radar. The model is kept simple, making it suitable for Monte Carlo methods, which allow the indispensable statistical evaluation of the broadly spread results. Finally, a method is presented that transfers multiple statistics regarding single interferers into a single environment. The computing time of the simulation grows linearly with the number of interfering radars, so the effects of vast numbers of interferers can be studied using this simulation model. Statistical evaluations of the detection performance degradation of a front-mounted radar in sample highway scenarios, containing up to ten interfering radar sensors, are performed in this paper.

Wireless power transfer (WPT) via coupled magnetic resonance is anencouraging technology to be applied in many fields. In this paper, a method using a circular coil spiral inductor structure to wirelessly transfer energy is proposed. It represents the characteristic of six parallel air core inductor mutually coupled in the free space for wireless power transfer system. Based on the analytical model and circuit theory, the relationship between the coil design parameters and the system performance is deduced, and the effects of the outer radius, inner radius, channel width and coil turns are thoroughly studied to improve the system performance at different axial distances and in lateral misalignment. Also, an elimination method for transmission efficiency dead-zone (TEDZ) is proposed. The proposed method utilizes angular rotation of the receiver (Px) to eliminate the zero-coupling point which causes TEDZ and boosts the coupling coefficient such that the TEDZ is eliminated, and the high efficiency region is extended.

A CPW-fed printed square slot antenna (PSSA) based on characteristic modes (CMs) theory is investigated for broadband circular polarization (CP). It consists of an I-shaped patch and CPW ground plane loaded with a rectangular stub, a pair of asymmetric inverted-L grounded strips, and a spiral slot to get CP radiation over a wide-angle range. CMs of this strip and slot loaded PSSA show that the entire structure takes participation to excite magnetic and electric modes to provide broadband performance. First six characteristic modes are excited using CPW feeding to find resonating frequencies and radiating behavior. The proposed antenna is fabricated over RO-3003 substrate material with a floor area of 20×20 mm². Experimental results showcase the broadband CP performance with wide 3-dB ARBW of 56 % (6.6-11.8 GHz) and impedance bandwidth (IBW) (|S11| ≤-10dB) about 115 % (4-11 GHz) which make it suitable for C-band and X-band wireless and satellite communication applications. The antenna has a peak gain about 5.5 dBi with good LHCP radiations in the broadside direction.

In this article, a novel dual-band omnidirectional antenna for WiFi applications is presented and investigated. The proposed antenna is mainly composed of two pairs of half-wavelength dipoles with different lengths. It is fed by a microstrip balun, which provides a good impedance matching for desired dual-band operation. The dimension of the proposed antenna is only 50 mm × 10 mm × 1 mm (0.4λ₀ × 0.08λ₀ × 0.008λ₀, and λ₀ is the wavelength of 2.4 GHz). The performance study of this dual-band omnidirectional antenna with different geometric parameters has been conducted. The final design is fabricated and measured, and the results exhibit a good impedance bandwidth of approximately 19.2% for |S₁₁| ≤ -10 dB ranging from 2.24 to 2.70 GHz centered at 2.4 GHz, and over 17.4% for |S₁₁| ≤ -10 dB ranging from 4.73 to 5.6 GHz centered at 5.0 GHz. This antenna also has a stable gain of 2.09~2.87 dBi and omnidirectional radiation patterns over the whole operating band. Dual-band coverage, stable omnidirectional radiation performance, simple structure, and miniaturized dimension make this antenna an excellent candidate for WiFi applications.

This article presents the design and optimization of multi-ring permanent magnet thrust bearing (PMTB) with an axial air gap between successive axial stacks. Larger air gap due to the inclusion of conductive materials needs to be critically analysed in permanent magnet bearings with eddy current damper. High conductivity materials can be filled in an axial air gap instead of a radial air gap to increase the required amount of damping. Three-dimensional (3D) mathematical model for load-carrying capacity for the said configuration is presented using the Coulombain model. The significance of an axial air gap between successive ring pairs in the configuration concerning maximization in the bearing characteristics is presented. Variables such as the number of axial stacks, an axial air gap between the successive rings, an inside radius of rotor ring magnets, and an inside radius of stator ring magnets are optimized at different air gap values for maximizing the load-carrying capacity and stiffness. A significant increase in the values of bearing characteristics is observed in the optimized configuration as compared to bearing with a single permanent magnet ring pair. Optimized PMTB with comparable load carrying capacity and stiffness values can be used to replace conventional bearings used in high-speed applications to improve system efficiency.

In this paper, a new cross section configuration of partially dielectric-filled rectangular waveguide (PDF-RW) is proposed and analyzed. It may beused when substrate integrated waveguides (SIWs) are designed such as to maximize the frequency bandwidth for insertion losses as low as possible. Imposing the boundary conditions for the electromagnetic field components, the equations for the cutoff frequencies and propagation constants are developed for the TE_m0 modes. It is shown that the cutoff frequency equations developed in this paper may also be used to analyze particular cases investigated by other authors. The ratio between the cutoff frequencies of the TE₂₀ and TE₁₀ modes is computed and represented graphically for different geometric dimensions of the proposed PDF-RW configuration. The conductor and dielectric losses for the TE₁₀ mode are computed as well, based on the results provided by the equations developed in this paper. The results obtained by using the proposed approach are compared to the HFSS (High-Frequency Structure Simulator) results, and very good agreement is observed between them.

In general, a single beam reflection can be realized by 2-bit coding metasurfaces. In order to obtain multi-beam reflection, a design method for coding sequence based on 2-bit coding metasurfaces is proposed, which can manipulate the direction of reflected beams by 2-bit addition rule and control the number of reflected beams by addition theorem on complex codes. This method simplifies the design process of coding sequence, and the direction and number of multi-beams can be flexibly designed. In this paper, the design of dual-beam reflection is taken as an example to illustrate the design process of coding sequence. Both simulation and measurement results show that the designed metasurface realizes the dual-beam reflection, and the direction of reflected beams is consistent with expectations. The proposed method is of great significance for the design of multi-beam reflection based on coding metasurfaces.

A six-element circular antenna array with Yagi-Uda corner reflector elements is proposed in order to achieve 360° beam-steering capability, high gain and cost-effective design objectives. The array element is mainly composed by a Yagi-Uda antenna, a corner reflector and a Wilkinson balun. For steering the main beam, instead of classical RF switching techniques, a virtual switching technique is offered. For this aim, each antenna element is connected to an affordable RF transceiver managed by a microcontroller. A USB hub is also used so that a computer operates all microcontrollers as peripheral devices. In this way, the switching operation can be performed in the software level. Furthermore, if every transceiver in the separate chain is set to a different frequency channel, a simultaneous communication is also possible with the help of the multithreading facility of the computer. In order to show the antenna array performance, the main antenna characteristics and test results are given. As a proof of concept, a wireless image collector scenario is also realized for a camera trap application. The results show that the circular antenna array design and switching technique work successfully.

A coplanar waveguide (CPW) fed uniplanar all-metallic antenna is proposed for mmWave 5G access points. The antenna has an impedance bandwidth from 26 to 30 GHz with a corresponding end-fire gain of 8 dBi at 28 GHz. The effective radiating volume is 0.0031 λ₀³ indicating a high gain yield for minimal physical footprint. The radiation efficiency is 99.5%, and the losses are primarily due to finite conductivity of copper. The pattern integrity is high across the band with cross-polarization level below 30 dB, due to lack of electrically thick dielectric substrate. Industry standard low-cost chemical etching technique is used for fabrication of the prototype. A compact, co-polarized stacked beam switching module is also proposed for wide angular coverage with three-ports. This module houses the proposed all-metallic antennas for beam switchability. A customized 3D-printed scaffolding using polylactic acide (PLA) is designed to house the proposed antennas. The antenna module has a wide angular coverage of ±50º. Since the proposed antenna has high radiation efficiency with high gain for minimal physical footprint, it could be a potential solution for mmWave 5G access points. Detailed simulated and measured results are presented.

In this study, plane wave diffraction by a perfect electromagnetic wedge which is lying between isorefractive media is investigated. The diffracted waves are constructed by using the relation between initial geometric optics waves and scattered waves at the transition boundaries. The uniform theory of diffraction method is used for derivation of the uniform wave expressions. Thus, obtained uniform expressions are analyzed numerically for different set of parameters.

A novel integrated compact antenna with photonic band gap (PBG) structure, having switching capability between lower and upper bands of 5G cellular communication is proposed. The proposed antenna can operate in the lower band (3.1 GHz to 3.5 GHz) as well as in the upper band (24 GHz to 27 GHz) of 5G cellular communication. Two radiating patches for the aforementioned frequency bands are developed in the same structure. A small patch for the upper-frequency band is inserted into a rectangular slot made in a large patch of the lower-frequency band. Both patches radiate at different times with the same ground. Two PIN diodes have been used to excite both patches at different times. The results indicate that the antenna has higher gain and wider bandwidth than the conventional antenna without a PBG structure.

A time domain hybrid method is presented to solve the coupling problem of non-parallel transmission lines (NPTLs) excited by ambient wave efficiently, which consists of transmission line (TL) equations, finite-difference time-domain (FDTD) method, and interpolation techniques. In this method, NPTLs are firstly divided into multiple independent transmission line segments according to the FDTD grids. Then the TL equations are applied to build the coupling models of these TL segments, which rely on the calculation precisions of per unit length (p.u.l) distribution parameters of NPTLs and equivalent sources of TL equations. Thus, the p.u.l parameters of NPTLs are derived from empirical formulas, and the equivalent sources are obtained by some linear interpolation schemes of electric fields on the edges of FDTD grids. Finally, the difference scheme of FDTD is utilized to discretize the TL equations to obtain the voltages and currents on NPTLs and terminal loads. The significant feature of this hybrid method is embodied by its synchronous calculations of space electromagnetic fields and transient responses on NPTLs in time domain. The accuracy of this presented method is testified by the numerical simulations of plane wave coupling to NPTLs on the ground and in the shielded cavity by comparing with FDTD-SPICE method and CST software.

We exploit the properties of differential geometry of minimal surfaces to introduce a novel approach for characterizing wavefronts. Since Gaussian and mean curvatures describe global and local properties of any differentiable surface, a method for characterizing wavefronts endowed with non--trivial topological features has been introduced. We provide experimental evidence that the wavefront of an l = 1 radio-vortex at 30 GHz can be fully characterized by exploiting the wavefront phase in the far field of the source, accessing a small portion of the beam only. A particular care is dedicated to distinguish diffraction effects from the intrinsic curvature of the helicoidal wavefront. Results are applicable to the local measurement of the topological charge and to the local detection of orbital angular momentum radiation at the millimetric wavelengths.