We demonstrate that the future sixth generation (6G) radio links can be utilized for sub-THz frequency imaging using narrow beamwidth, high gain, lens antennas. Two different lenses, a bullet or hemispherical shape, were used in radio link setup (220-380 GHz) for an imaging application. Lenses performed with the gain of 28 dBi, 25 dBi, and narrowed the beamwidths of 1° and 2.5°. Plants were used as imaging objects, and their impacts on radio beams were studied. For assessment, the radio link path loss parameter was -48.5 dB, -53.2 dB, and -57.1 dB with the frequency 220 GHz, 300 GHz, and 330 GHz, respectively. Also, the impact of the radio link distance on the imaging was studied by 50 cm and 2 m link distances. In addition, the 3D image was acquired using the phase component of the image, and it showed the leaf surface roughness and the thickness, which was similar to the measured value.

Beamforming can steer the mainlobe of the beam pattern towards the desired signal and set several nulls in the directions of interference signals by adjusting the excitation weights of array elements. These days, a range of meta-heuristic algorithms have been utilized for beamforming of antenna arrays. However, most of the methods are applied to linear arrays and rarely to planar arrays. In this paper, a novel variant of binary particle swarm optimization (BPSO) is proposed at first, where the global search ability and the local optimization ability are both taken into account. Then, the fitness function including the term of peak sidelobe level (PSLL) is constructed, and the improved BPSO is applied to the beamforming of uniform planar array (UPA). Finally, simulation results demonstrate that the proposed algorithm is not only able to suppress PSLL effectively, but also able to form deeper nulls than that of linearly constrained minimum variance (LCMV).

A novel wide beamwidth microstrip patch antenna fed by a 1:5 unequal Wilkinson power divider with a low profile of 0.027λ₀ is presented. A circular patch and an independent feeding concentric metal ring can realize the broad half-power beamwidth (HPBW) in the far field. A 1:5 unequal Wilkinson power divider is designed as the antenna feed. The HPBWs of the antenna reach 258° and 267° in XZ-plane and YZ-plane, respectively, covering the whole upper half space at central frequency (2.54 GHz). The results of simulation and measurement show great consistency.

Nowadays, due to the ever-increasing number of electronic devices and communication systems that use high-frequency electromagnetic waves, a significant level of electromagnetic energy is available in the environment that is not entirely used. In this work, a complete electromagnetic harvesting system using a rectenna is proposed to collect this energy and feed a temperature measurement module. The rectenna is constituted by a combination of a microstrip antenna that captures the electromagnetic energy and a rectifier circuit that converts it into electric energy in direct current (DC) form to feed ultra-low-power loads. The proposed system uses a rectangular microstrip antenna, designed and optimized by using the Computer Simulation Technology (CST^®) software to operate at 2.45 GHz. This designed antenna presents a measured reflection coefficient lower than -20 dB at the operating frequency with a maximum gain equal to 7.26 dB. In addition, a voltage doubler rectifier circuit is designed and optimized by using the Advanced Design System (ADS^®) to match the impedance of the designed antenna to reduce the reflection losses between these two modules, achieving maximum measured efficiency of approximately 33%. Furthermore, a boost converter circuit is designed for the power management between collected and delivered powers to the sensor and to provide appropriate voltage levels to feed the temperature measurement module. This module consists of an ultra-low-power microcontroller and a temperature sensor that operates in the range of 1.8-3.6 V. The procedures for designing and testing each module of this system are detailed. Finally, a prototype is built and tested under different operating conditions to confirm its functionality and feasibility. These tests show that the proposed system can operate without batteries, only with the harvested electromagnetic energy dispersed in the environment, even from modulated and pulsating sources, as is the case of commercial routers.

A free-space and non-invasive measurement technique to characterize the dielectric properties of a non-magnetic NASA-developed composite material is presented. To estimate the dielectric properties of the composite material, the material under test is placed as a superstrate over a pre-characterized benchmark antenna. The reflection coefficients and gain of the superstrate-loaded antenna are then utilized to estimate the relative permittivity and loss tangent of the composite under test, respectively. Using numerical analyses and measurements of the benchmark antenna loaded with the superstrate, the aforementioned properties are estimated to be 6 and ~0.12, respectively. To validate the accuracy of the method, a square microstrip patch antenna is also designed on a grounded NASA-developed composite material at the ISM band.

This paper proposes an orthogonal dual-feed microstrip patch antenna (MPA) that achieves multi-band resonance along with circular polarization at its primary band of 5G cellular communication. The proposed antenna is simpler than other designs to fulfill extreme data rates and minimum infrastructure requirements. This MPA is designed by taking most care for maintaining the isolation between ports with feasibility for physical fabrication. The HFSS based optimally designed proposed MPA resonates simultaneously at 3.48 GHz (3.3 GHz-3.7 GHz) band, 6.24 GHz (5.925 GHz-6.425 GHz) band, and 7.5 GHz (7.11 GHz-7.9 GHz) bands. The modes achieved for these three bands are TM₀₁, TM₁₁, and TM₁₂ for 3.48 GHz, 6.24 GHz, and 7.5 GHz, respectively. The bandwidths achieved for the bands mentioned above are 160 MHz (4.57%), 330 MHz (5.27%), and 340 MHz (4.53%), respectively. The corresponding gains achieved are 9.8 dB, 5.06 dB, and 7.58 dB. The proposed MPA structure prototype is fabricated, and its performances are measured. The measured S11 for fabricated MPA is close to the resonating frequency found using HFSS simulation. The proposed MPA structure is also modeled and simulated in a MATLAB simulation environment. Performance parameters of the proposed MPA obtained in MATLAB and HFSS are compared and matched reasonably. The proposed MPA structure and its arrays are used for 5G cellular sites as a real-time application in a MATLAB simulation environment. Different test scenarios are created in MATLAB. SINR is visualized for the entire cellular area, and signal strengths are also fetched at the receiver sites.

This paper presents a paattern synthesis method to generate dual-beam patterns of a rectangular planar array of isotropic antennas in a particular scanning angle using Evolution Algorithms. The dual-beam patterns are cosec₂ pattern and pencil beam pattern, and both the patterns are steered to an elevation angle of 20 degrees (θ = 20˚). Moreover, each pattern is synthesized in three azimuth planes (φ = 0˚, 5˚, and 10˚). The isotropic elements are uniformly spaced, and nonuniform excitations are applied to achieve the desired patterns. These patterns are obtained by applying the optimum set of common elements amplitude and phases for the cosecant-squared pattern only. The optimum 4-bit discrete amplitudes and 5-bit discrete phases are produced using using Differential Evolutionary (DE) Algorithm, Genetic Algorithm (GA), Particle Swarm Optimization (PSO) Algorithm, and Firefly Algorithm (FA). These discrete excitations are helpful to reduce the Dynamic Range Ratio (DRR) and the design complexity of the feed networks. The excitations are also verified in a range of arbitrarily chosen azimuth planes. The patterns are generated in the same steering angle with minor variations of the desired parameters. The outcomes established the superiority of DE over PSO, GA, and the effectiveness of the proposed method.

This article reports a multilayer implantable biosensor for a continuous glucose monitoring system, tested on rats to determine the relationship between intravenous glucose level and resonance frequency of implant antenna sensor. An implantable antenna sensor with the volume 330.9 mm³ is tested in three rats as an animal model. This antenna biosensor operates in the Medical Implant Communication Service frequency band (402-405 MHz) with the simulated and measured maximum gains of -13.33 and -21.1 dB, respectively. The specific absorption rate obtained is within the standard limits. An oral glucose tolerance test is proposed to obtain the variation in blood glucose level in the animal's body during measurement. The resonance frequency shift and the corresponding blood glucose level are observed at a regular interval of 30 minutes. A frequency shift of 4.94 kHz per mg/dL is observed. Also, the results related to the reflection coefficient and the factors affecting sensor performance are discussed. The biosensor performance is validated using the proposed simple linear regression model.

An electrically small ultra-wideband (UWB) antenna to cater to the need for UWB communication suitable for today's small gadgets is presented. The antenna is realized on a substrate of relative dielectric permittivity 4.4, loss tangent 0.02 and height 1.6 mm. The overall dimension of the antenna is 21 mm×16 mm×1.6 mm (0.217λ_min×0.165λ_min×0.0165λ_min), where λ_min is the wavelength corresponding to the antenna's lowest operating frequency in free-space 3.1 GHz). The small `k<sub>min</sub>a' value of 0.856 of the antenna, where k<sub>min</sub> is the wavenumber corresponding to λ<sub>min</sub>, and `a' is the radius of the sphere that can fully enclose the antenna, is electrically small. The antenna operates at the FCC recommended UWB frequency range from 3.1 GHz to 10.6 GHz with a reasonably good 2:1 voltage standing wave ratio (VSWR) impedance bandwidth. A prototype of the proposed antenna is fabricated, and different radiation characteristics of the antenna in the frequency and time domain are measured and validated by simulation. The high pulse fidelity for different antenna orientations and very small group delay in the operating frequency band exhibit insignificant pulse distortion. The equivalent isotropically radiated power (EIRP) of the antenna satisfies the FCC mask in the entire UWB. The maximum gain and efficiency achieved within the UWB are 3.95 dBi and 93% respectively. Radiation characteristics of the antenna in the UWB are studied in an anechoic chamber using Agilent PNA E 8362B.

This paper presents a novel variable leakage flux flux-intensifying motor (VLF-FIM) to improve flux-weakening ability. The innovation lies in the variable leakage flux property and the characteristic of L_d>L_q. The two characteristics can be achieved by the adoption of magnetic barriers and magnetic bridges. Consequently, the flux-weakening ability is enhanced. Then, the topology structure and operation principle of the proposed machine are introduced. Based on the two-dimensional finite element method (2DFEM), the electromagnetic performances of the proposed motor are analyzed and compared with the conventional interior permanent magnet motor (CIPMM) in detail. The performances mainly include torque, flux-weakening ability, constant power speed range (CPSR), irreversible demagnetization risk of the PM, structural strength, etc. Finally, the results show that the proposed motor has some advantages, such as good flux-weakening ability, a wide constant power range, and a large high-efficiency area. In addition, it verifies the effectiveness of the proposed method in improving the flux-weakening ability of the motor.

A multi-stack anisotropic cylindrical dielectric resonator antenna with high gain and wide bandwidth is reported. This antenna is designed with three different stacks, and each stack consists of a multilayer dielectric structure to emulate uniaxial anisotropy. Multi-stack, multilayer structure is responsible for producing wide bandwidth and high gain. In addition, the antenna is surrounded by cylindrical metallic cavity to increase directivity in broadside direction. Similar simulated and measured results indicate a wide impedance bandwidth of 37% along with a maximum gain 9.25 dB.

Broadband variations of a proximity fed circular microstrip antenna gap-coupled with narrow annular sectoral patches are proposed. The gap-coupling of pairs of parasitic annular sectors along the x- and y-axes of the fed patch tunes the spacing in between the fundamental modes on the respective patches that yields wider bandwidth. A maximum bandwidth of 728 MHz (55%) offering peak gain of nearly 9 dBi is obtained in the circular patch gap-coupled with four pairs of annular sectors along the x-axis. This bandwidth is around 13% larger than the bandwidth offered by a single circular microstrip antenna. Instead of using multiple sectoral patches, a gap-coupled design of circular patch with a stub loaded annular sectoral patch is presented. The stub tunes TM₀₂ mode frequency with reference to the fundamental modes on the circular and sectoral patches that yields bandwidth of 660 MHz (51%). Resonant length formulation and subsequent design methodology for all the proposed gap coupled configurations are presented, which helps in the re-designing of similar antennas at the given fundamental mode frequency. All the optimum and re-designed antennas are fabricated, and the measured results shows close agreement with the simulations.

In this paper, a novel low-profile and dual-polarized antenna is presented. The antenna is composed of two pairs of rhombic dipoles excited by two orthogonal baluns. The broadband characteristic is achieved by introducing a metal ring under the rhombic dipole, and the radiation pattern beam widths are also improved. Based on the antenna unit, a 2-element antenna array is designed, fabricated, and measured. The relative bandwidth (standing wave less than 1.5) of the antenna is 45.1%, and the port isolation is greater than 27 dB, whereas the cross-polarization level maintains lower than 16 dB in the the frequency band of 2.4-3.8 GHz. The measured results are in good agreement with the simulated ones. This proposed antenna also has low profile characteristics, and the profile height is 20.8 mm, which is less than one quarter of the wavelength (24.2 mm) of the central frequency point (f = 3.1 GHz).

A dual-band Wilkinson power divider covering comprehensive frequency ratios with improved Out-of-Band rejection is proposed with the use of only a resistor. In millimeter-wave range, the established lumped element based design with a wide range of frequency ratio suffers from the nonexistence of tiny required values and the difficulties of integrating them in the proposed designs. To tackle some of the more common millimeter-wave frequency bands challenges, the RLC is substituted in the design by transmission lines and a single resistor. The design parameters and rules are derived theoretically using even/odd mode analysis, and it takes into consideration the Out-of-Band performance. For validation, three different dual-frequency bands are studied (5.8-28 GHz, 20-35 GHz, and 28-35 GHz). The simulated and experimental results exhibit all the advantages of the proposed Wilkinson power divider, succeeding in boosting multi-functional and multi-standard RF and mm-wave front-ends for communication systems.

In this paper, a compact and reconfigurable rectangular substrate integrated waveguide structure dual-mode configuration based dual-band band-pass filter has been presented for 5G communication and milli-meter-waves. The dual-band bandpass filter is realized by utilizing the two pairs of dumbbell-shaped defected ground structure. The dumbbell-shaped defected ground structures etched on both the ground and the top side of the cavity have been used to produce transmission zeros, minimize the circuit size, and enhance the passband characteristics at a particular frequency of operations. In an effort to demonstrate the proposed dual-band substrate integrated waveguide band-pass filter, the proposed configuration has been designed and fabricated at the 28.3 GHz and 38.5 GHz frequency using low-cost PCB technique. The centre frequency of the second pass-band has been easily tuned using the geometrical parameters of the filter to achieve the desired applications in the 5G frequency band. Furthermore, the measured in-band return loss (rejection attenuation) of the two bands is approximately better than 26 dB and 28 dB respectively. The insertion loss of not more than 01 dB for both bands of the filter has been achieved. This dual-band filter operating at the licensed frequencies for the 5G spectrum bands renders this filter appropriate for numerous 5G and millimeter-wave communication applications.

A dual band flexible antenna for applications at 900 and 2450 MHz is proposed in this paper. The antenna offers a compact size of 0.23λ_o × 0.120λ_o × 0.0007λ_o, where λ_o is the wavelength at the lower resonance. The antenna comprises a simple geometrical structure consisting of a W-shaped serpentine structure fed by a microstrip line, while a Defected Ground Structure (DGS) technique was utilized with a partial ground plane to achieve wide operational bandwidth. An additional capacitor was loaded in between the slots to achieve a higher resonance, thus resulting in a compact dual band antenna. Various performance parameters were analyzed, and results were compared with the measured ones. The antenna offers good performance in terms of size, bandwidth, gain, and radiation pattern and thus increases the potential of the proposed antenna for both rigid and flexible devices.

Exceptional points are spectral singularities in non-Hermitian systems at which two or more eigenvalues and their corresponding eigenvectors simultaneously coalesce. Originating from quantum theory, exceptional points have attracted significant attention in optics and photonics because their emergence in systems with nonconservative gain and loss elements can give rise to many counterintuitive phenomena. Metasurfaces - two-dimensional artificial electromagnetic materials structured at the subwavelength scale - can provide a versatile platform for exploring such non-Hermitian phenomena through the addition of dissipation and amplification within their unit cells. These concepts enable a wide range of exotic phenomena, including unidirectional propagation, adiabatic mode conversion, and ultrasensitive measurements, which can be harnessed for technological applications. In this article, we review the recent advances in exceptional-point and non-Hermitian metasurfaces. We introduce the basic theory of exceptional point and non-Hermiticity in metasurfaces, highlight important achievements and applications, and discuss the future opportunities of non-Hermitian metasurfaces from basic science to emerging technologies.

When particle swarm optimization (PSO) is used to identify the parameters of permanent magnet synchronous motor (PMSM), the movement of particles is not selective, which makes the algorithm easy to fall into the local optimum, and the accuracy is poor. The simulated annealing particle swarm optimization (SAPSO) improves the accuracy and evolution speed, but SAPSO has redundant iteration problems. To solve these problems, a motor parameter identification method based on fast backfire double anneal particle swarm optimization (FBDAPSO) is proposed. By reducing the optimization time and quickly tempering and annealing the "misunderstood" difference, the motor adjustable model and fitness function are designed, and the number of iterations is constantly reset to achieve the effect of online identification. Under different working conditions, simulated and experimental results show that the proposed method can quickly and accurately identify the four parameters of the motor's stator, winding resistance, stator winding d-axis inductance, stator winding q-axis inductance and permanent magnet flux linkage at the same time, compared with the traditional method of parameter identification, and it has better accuracy, rapidity, and robustness.

In this letter, a compact dual-band patch antenna based on ball grid array (BGA) packaging for 5G mmWave is proposed. The patch antenna adopts a U-slot and a shorting pin to achieve dual-band operation of 28 GHz and 37 GHz. A single-layer FR4 substrate provides cost-effective features for the massive application. The BGA packaging not only reduces the size but also enables the antenna to be surface-mounted with other components in the same package, which improves the integration. The antenna has been fabricated and measured, and an acceptable agreement was obtained between the simulation and measurement results.

A novel coplanar waveguide (CPW) fed wide slot antenna for broadband circular polarization (CP) operation is proposed in this letter. Utilizing an asymmetrical ground plane and an open slot, broadband axial ratio and good impedance characteristics can be obtained in the middle and low bands. The perturbation patch on the right side of the wide slot excites the upper-band CP mode. By adjusting the upper-part feedline and the wide slot structure, the axial ratio performance can be optimized to a wideband axial ratio bandwidth (ARBW). Compared with wide slot antennas of similar size, the proposed antenna has a simpler structure while achieving a wider ARBW. The proposed antenna has been fabricated and tested. The measured results show that the -10 dB impedance bandwidth (ZBW) is 2.40-7.55 GHz (103.5%); 3-dB ARBW is 2.47-6.2 GHz (86.0%); and the peak gain is about 4 dBic. Right-hand circular polarization (RHCP) radiation pattern is achieved in +z direction. The proposed antenna can be used in WLAN/WiMAX applications and various wireless communication systems which require broadband ZBW and ARBW.