A Clown-shaped patch antenna for super wideband applications is presented. The radiator is placed on a 1.6 mm thick, RT/Duroid 5880 substrate and is fed using a 50 Ω symmetric coplanar waveguide. The size of the proposed antenna is 26 × 27 mm² (0.256λ_L × 0.266λ_L, where λ_L is the wavelength at the lower band edge frequency i.e. 2.96 GHz). The radiator is a combination of an ellipse, a rectangle, and a triangle. An impedance bandwidth of 2.96 GHz to more than 100 GHz (i.e. more than 33.78:1 ratio bandwidth) is achieved. Nearly-omnidirectional radiation patterns with an average gain of 6 dBi are achieved. A fractional bandwidth greater than 188.5%, a size reduction of ~97%, and a comparable bandwidth dimension ratio of 2768 are achieved. The investigated antenna has additional advantages like compactness, planar geometry, and super-wide bandwidth.

The aim of this study is to provide a topological optimization method for ship detection in synthetic aperture radar (SAR) imagery. The method consists of three steps: pre-processing, sparse representation and classification. For the first step, the variational model is used for SAR image filtering. For the second step, the curvature of the surface manifold is constructed for sparse representation of target. For the third step, the topological derivative method is adopted to locate the target. Experiments show that the proposed method is effective in reducing false alarms, and obtains a satisfactory detection performance.

A scheme for radar cross section (RCS) reduction of microstrip antenna array in wideband using artificial magnetic conductors (AMC), without compromising the radiation characteristics of the antenna array, is proposed. This design is based on the principle of passive cancellation. The novelty is that the reflection characteristics of the microstrip antenna array are also taken into consideration during the design process of AMCs. The aperiodic configuration is composed of three kinds of AMC lattices with selected dimensions and is applied to the design of microstrip antenna array for the purpose of RCS reduction. The simulated results show that the monostatic RCS is reduced over a wideband from 15.2 to 35 GHz (about 79% relative bandwidth), covering the operation band (20-20.75 GHz) of the antenna array. In addition, compared with the periodic configuration, it has about 4 dB lower maximum bistatic RCS.

In this article, a 28 GHz endfire antenna based on ball grid array (BGA) packaging is proposed for the 5G mmWave new radio (NR). The antenna is composed of a pair of dipole patches fed by a substrate integrated waveguide (SIW). Besides, quasi-coaxial vertical transition and transition from grounded coplanar waveguide (GCPW) to SIW are designed on the substrate to achieve compact size. The substrate is based on a single-layer printed circuit board (PCB), which can meet the cost-effectiveness requirements of the 5G application. Meanwhile, the proposed antenna can be easily integrated with other surface-mount devices by using the BGA packaging. In particular, it can be mounted near the RF front-end chipset to improve system performance. Finally, the prototype is manufactured and verified. Experimental results show that the -10 dB bandwidth of the proposed antenna is 5.35% in the range of 27.3 to 28.8 GHz, and the peak gain achieves 4.4 dBi at 29 GHz.

In high speed indoor communication, ultra-wideband (UWB) plays a crucial role. UWB contains several other narrow band systems, which give interference. In order to reject these narrow bands present in UWB system, a novel multilayer step via electromagnetic band gap (MS-EBG) structure to vary the band-notch of UWB monopole printed antenna is presented in this work. The proposed EBG consists of grooved substrate with step via arrangement. These grooved substrate allow for the deposition of the liquids with different dielectric constants to achieve the variations in band gap center frequency of EBG. The microstrip line based model with equivalent circuit diagram of MS-EBG is developed with experimental results using suspended micro strip line (SML) method, with different liquids like kerosene, sea water, mineral oil, without grooved substrate, etc. The simulated and experimental results show liquid sensing ability of the proposed MS-EBG structure. The application of MS-EBG to vary the band notch in UWB hexagonal monopole antenna (HMA) is also demonstrated. Simulated and experimental results show noticeable variation in the band notch center frequency with different liquids deposited in the grooved substrate. The proposed method required only liquid change arrangement to get desired band notch in UWB monopole antenna. Compared to electrical and mechanical method to get band notch in UWB monopole antenna, the proposed method works without any power supply, active devices and additional complex arrangement.

Electromagnetic properties of a planar metallic metasurface with the design inspired by Babinet's principle are numerically studied. The metasurface is constructed from a metal plate perforated by coaxial-sector apertures. It is shown that the chosen coaxial-sector apertures make it possible to obtain a wider operating range of the metasurface than those composed of apertures of other shapes (e.g. round or rectangle). Moreover, the proposed metasurface performs an efficient polarization conversion of the linearly polarized wave to elliptically and circularly polarized ones in the reflected field.

This paper presents a method for rapid microwave imaging of traumatic brain injury based on scattering parameters. The algorithm uses the integer order Bessel function and Born approximation, which converts nonlinear inverse scattering problem into linear problem. After truncated singular value decomposition, imaging can be performed without iteration. Simulations and experiments show that the algorithm can not only reduce the amount of calculation for fast imaging, but also accurately image a brain hematoma or foreign body.

This letter proposes a miniature bow-tie antenna element and its 2 × 2 arrays based on ball grid array (BGA) packaging technology for 5G millimeter-wave new radio (NR) applications. The antenna substrate uses ultra-economical single-layer FR4 printed circuit boards (PCB) to reduce manufacturing costs. By adopting solder balls, the antenna achieves the BGA packaging and realizes the surface mounting function. One bow-tie patch is excited by a plated through-hole (PTH) connected to the feeding point. The other bow-tie patch is directly short connected to the ground plane by another PTH. Besides, the bottom ground plane can be equivalent to a reflector, allowing the antenna element and array to obtain broadside radiation. For ease of integration, the input impedance of the antenna is set to 50 Ω. The measurement results show that the -10 dB bandwidth of the antenna element is 21% covering 25.2 to 31.1 GHz. The measured peak gains of the antenna element and the 2 × 2 arrays are 7.6 and 10.75 dBi, respectively. The proposed antenna element and array cover N257 (26.5-29.5 GHz) and N261 (27.5-28.35 GHz) bands. It is very suitable for the 5G millimeter-wave application.

A 37-43 GHz endfire antenna based on ball grid array (BGA) packaging is proposed for the fifth-generation (5G) wireless system. The antenna consists of a miniaturized radiator and reflector. Besides, the radiator is fed by a substrate integrated waveguide (SIW). Furthermore, the RF transition from the SIW to grounded coplanar waveguide (GCPW) and vertical quasi-coaxial is realized on the substrate. The antenna is implemented on a single-layer substrate using standard printed circuit board (PCB) technology to reduce costs. Then, the cost-effective antenna element is reflow soldered with solder balls to form a BGA packaging. The advantages of the BGA packaging and the three-dimensional (3D) integration are discussed in detail. The miniature packaging achieves a compact size of 7 mm × 3.4 mm × 0.6 mm. Finally, a prototype was manufactured to verify the performance. The measurement results show that the proposed antenna is a good candidate for 5G millimeter-wave (mmWave) New Radio (NR) applications.

The letter presents a compact, cost-effective, and surface-mount patch antenna element for 5G millimeter-wave (mmWave) system integration. The antenna element adopts ball grid array (BGA) packaging technology to achieve surface mount function, which can be applied to highly integrated systems. By adding a ring slot on the radiating patch, the proposed antenna obtains a wider impedance bandwidth. The antenna prototype has been simulated, manufactured, and verified. The proposed antenna element size is 5 mm × 5 mm × 1.3 mm. The measurement results show that the proposed antenna element can be used in the N257 (26.5 to 29.5 GHz) and N261 (27.5-28.35 GHz) frequency bands.

The resonant frequency will be changed, and the load voltage will be unstable with misalignments and load variations in wireless power transfer (WPT) systems. In this paper, the expression for solving the resonant frequency is obtained. The calculation result shows that the resonant frequency is changed with the changes of misalignment and load. First, a new control method of frequency tracking with a Fuzzy proportional-integral (PI) compound controller is proposed, which can eliminate the overshoot of resonant frequency and improve the speed of frequency tracking. Second, a mixed-modulation method for adjusting frequency and voltage is further proposed, which is mainly composed of the selection algorithm of the duty cycle, the phase-shifting angle calculation, and the method of frequency tracking based on the Fuzzy PI compound controller. The appropriate duty cycle is obtained by the selection algorithm of the duty cycle to adjust the load voltage. The phase-shifting angles of different duty cycles are obtained by the phase-shifting angle calculation, which play a role in adjusting the resonant frequency by combining the Fuzzy PI compound controller. The proposed method can not only make the system keep a resonant state, but also make the output voltage across the load stable. A WPT system via magnetically coupled resonance is designed. Calculation and simulation results validating the superiority of the proposed method are given.

In this paper, we derived Analytical Kirchhoff Solutions (AKS) for bistatic scattering near the specular directions at P band and L band for applications in Signals of Opportunity (SoOp). The land surface profiles are divided into three scales: microwave roughness f₁, fine scale topography f₂, and coarse scale 30-meter DEM f₃. The microwave roughness and the fine scale topography are treated as random rough surfaces, while the coarse scale topography from DEM data are treated as deterministic planar patches. The salient features of the AKS model are (i) analytical expressions are obtained for both coherent waves and incoherent waves, (ii) Monte Carlo simulations are not required making the AKS computationally efficient, (iii) the analytical solutions are expressed in terms of the spectrum, so that the dividing line between microwave roughness and fine scale topography is not required, and the rough surface spectrum derived from lidar elevation measurements can be incorporated directly. The results of the three approaches, AKS, the Numerical Kirchhoff Approach (NKA) and the Fine Scale Partial Coherent Patch (FPCP) model, are indistinguishable for both the coherent waves and the incoherent waves. The agreements validate the AKS and FPCP approaches as NKA is a brute force accurate method based on Kirchhoff integral using 2 cm discretization and high-performance computers. Results show that the f₂ profiles of fine scale topography have significant effects. The results of three Kirchhoff approaches fall in-between the results of the two versions of Geometric Optics (GO) approximations to the Kirchhoff integral [1, 2]. The two GO versions are with and without attenuation due to microwave roughness. The GO with microwave attenuation is also known as the ``Improved Geometric Optics Model (IGOM)''. Numerical results of coherent waves and incoherent waves are illustrated for remote sensing of snow and soil moisture at P band and L band. For P band, the histograms of the phase are shown. Results of the coherent waves are dependent on the sizes of the area as well as topographical elevations and slopes. AKS results are used to illustrate the coherent waves at P band on area sizes up to 1.5 km using 30-meter DEM topography elevations and derived slopes at Sanford, Brazos Peak, and Lobato Tank, Colorado, USA. For L band, the AKS results of Cross-Track are in good agreement with CYGNSS data over San Luis Valley, USA. In comparing CPU, it takes merely 25 seconds on a single CPU core for AKS to compute for a 15 km by 15 km DDM pixel which has 250000 DEM 30-meter patches. The CPU for AKS is slightly more than the 20 seconds required for GO.

A MIMO antenna with ACS- asymmetric coplanar strip feeding technique with compact size for UWB applications of band-notched features is presented. The proposed MIMO antenna contains two orthogonally placed rectangular-shaped radiating elements. The orthogonal mechanism of placement of radiating elements provides a good amount of isolation from 3.09 GHz to 11.13 GHz. The size of the antenna is 27 × 27 mm². The isolation is more than 17 dB for most of the UWB range. The proposed MIMO antenna represents nearly omnidirectional radiation pattern and low value of envelope correlation coefficient. Because of the usage of ACS feeding techniques, the antenna size is reduced, and it is a uniplanar structure. The diversity performance of the MIMO antenna is explained in terms of ECC-Envelope Correlation Coefficient, DG-Diversity Gain, and TARC-Total Active Reflection coefficient.

RAdio Detection And Ranging (RADAR) is an essential tool used extensively to detect a target's presence within the vicinity characterized by the range of the RADAR. In order to localize the target, Direction of Departure (DOD) and Direction of Arrival (DOA) estimations are utilized. To make it more convenient, a bistatic multiple input multiple output (MIMO) configuration is exploited to deduce the position of a target through the triangulation method easily. Furthermore, due to the maneuvering of targets in space, more robust direction finding solutions can be derived using Time-Frequency (TF) representations. Thus, this paper aims to leverage the benefits of TF analysis for the estimation of DOD and DOA jointly for a bistatic MIMO radar. The performance of the considered method is numerically evaluated and is compared against the conventional algorithms that do not use TF tools and as well compared against the Cramer Rao Lower Bound (CRLB). The results show that TF based approach may be a promising candidate in terms of its robustness against channel noise. Also, the performance of the TF based DOD-DOA estimates is studied in terms of their consistency and resolvability of targets which measures the performance in a multi-target environment. Finally, the use-case of TF based estimation to solve the problem in the presence of coherent targets is analysed through simulations and inferred.

An integrated wireless impulse generator has been designed, simulated, fabricated and tested. Switched oscillator topology has been used as an impulse generator. A switched oscillator consists of a low impedance transmission line, which is charged by a DC source with a large input impedance. The transmission line is connected to a fast closing switch at one end and a high feed-point impedance antenna at the other end. After charging the transmission line, closing the fast switch short circuits the transmission line, resulting in a transient wave propagating toward the antenna. The mismatch between transmission line characteristic impedance and the antenna feed point impedance causes a reflection at the antenna terminal. Due to the short circuit at switch terminal, the reflected signal will reflect back at the switch terminal as well. This back and forth reflection generates a series of pulses at the antenna terminal which will be radiated by the antenna. The switched oscillator impulse generator is designed to operate in the industrial, scientific and medical (ISM) radio frequency band.

In this article, a novel Hexagonal Split-Ring Resonator enclosed Circular Split-Ring Resonator (HSRR-CSRR) inspired printed antenna is presented for sub-6 GHz 5G NR and IEEE 802.11ba/be applications. The proposed antenna comprises an HSRR-CSRR and a D-SHSRR metamaterial unit cell with a partial ground plane. The designed antenna is printed on a low-cost FR-4 substrate with dielectric constant εr of 4.4, thickness of 1.6 mm, and loss tangent of 0.02. An HSRR-CSRR metamaterial structure is designed to get the three distinct resonance frequencies at 3.5 GHz, 5.05 GHz, and 6.2 GHz, respectively. To cover the entire band of Sub-6 GHz 5G NR (5-6 GHz), a Double-slit Single Hexagonal Split Ring Resonator (D-SHSRR) is designed for 5.8 GHz and loaded along with the HSRR-CSRR. The operating principle, equivalent circuit, and parametric extraction of the HSRR-CSRR structure are examined. Compared to the conventional antenna, the proposed antenna has a compact size of (0.38λ_g×0.52λ_g×0.03λ_g). The antenna parameters have been investigated using Ansys HFSS 15.0 software. The measured and simulated results are in good agreement.

This paper presents an efficient method to redesign a horn-fed, double-curvature reflector antenna. It helps reconstruct or repair the reflector according to a correct reference or analyze its radiation characteristics through full-wave electromagnetic simulations. The proposed method mainly consists of five stages. At first, it is necessary to obtain initial data in the form of three-dimensional coordinates of a sufficient number of points sampled from the reflector's different surface areas, especially from its central section curve and its peripheral contour. Then, the best-fitting surface to the sampled points is found using geometrical-optics (GO)-based formulations in an invasive weed optimization (IWO) algorithm. The GO relations extend the reflector laterally using elevation angle, horizontal, or focal point strips. As these are intrinsic formulations for designing doubly-curved reflectors, the fitted surface can resolve the possible defects in the reference reflector's geometryor inaccuracies in the sampled information partly. For this purpose, the reflector's central section curve is estimated by fitting a fifth-degree polynomial curve to the data sampled from it. Also, two kinds of errors, which are based on Euclidean distances, define the optimization algorithm cost function for more reliable surface fitting. In the third stage, the fitted surface's peripheral contour is adjusted to match the outline of the reference reflector using the points sampled from this section. In stage four, the redesigned reflector in the form of a point cloud is converted to a .stl file format for further simulation in a full-wave electromagnetic software. Finally, the similarity between the redesigned and reference reflectors' radiation patterns is examined using a radiation-based cost function in an iterative process, and the previously devised four stages repeat until appropriate results are obtained. In particular, an already designed and fabricated UHF band, doubly-curved reflector antenna, capable of generating a cosecant-squared radiation pattern in the elevation plane and narrow in the azimuth, is redesigned using 99 points sampled from it. It is found that horizontal strips can best fit the reflector with the small normalized error about 3 mm at the end of the IWO algorithm, indicating a nearly perfect geometrical similarity between the redesigned and reference reflectors. For further verification of the suggested method, the redesigned reflector's radiation pattern is simulated in CST simulation software, and the results are compared with the measured radiation pattern of the fabricated reflector and the simulated radiation pattern of the antenna's initial CAD model in the azimuth and elevation planes. Specifically for the redesigned antenna, the amounts of HPBW and sidelobe level in the azimuth plane are about 2.6° and 29.85 dB, respectively. Also, the amounts of gain, HPBW, and predefined parameters of α and β in the elevation plane are 28.25 dB, 13.5°, 5.07 dB, and 11.7°, respectively. All of the measured and simulated results are in good correspondence with each other, suggesting that the proposed method is a secure solution for redesigning double-curvature reflector antennas precisely and efficiently.

Valve radiator blockage is a serious problem endangering the safety of thyristor. At present, there are no effective methods for blockage evaluation and monitoring. This paper analyzes the heat dissipation state of a radiator under different blocking conditions and divides it into abnormal heat dissipation and normal heat dissipation. Then, based on reliability theory, the tolerance index ψ for blockage and the probability index θ for overheating are proposed to evaluate the blockage hazard of the thyristor. Also, the thermal circuit model of the valve group is established to monitor radiator blockage. According to the model, the corresponding relationship between radiator blockage and valve temperature distribution is solved, and the blockage detects index based on device temperature is given to judge radiator block. Through the infrared monitoring temperature solution, judgment of radiator blockage is consistent with the set blockage.

A bearingless induction motor (BL-IM) is a new type of motor integrating suspension and rotation functions. Higher requirements are put forward for its suspension performance. Due to the material advantages of a new type of amorphous alloy with high magnetic conductivity, low loss and low coercivity, it is considered to be used in the BL-IM rotor to reduce iron loss and improve the electromagnetic performance of the BL-IM. Finite element analysis software is used to analyze the performance of two different kinds of motors with the rotors made of conventional silicon steel and amorphous alloy respectively. The magnetic field density distribution, torque, speed, and radial force are compared between the two motors. The results show that the speed of amorphous alloy motor increases faster, and the rotor has better suspension characteristics. Moreover, the amorphous alloy material has a smaller density; the material properties can effectively reduce the weight of the motor; it is beneficial to the operation of the BL-IM in special environments.

Alzheimer's disease (AD) is a degenerative disease of the nervous system that often occurs in the elderly. As magnetic resonance imaging (MRI) and positron emission tomography (PET) reflect the brain's anatomical changes and functional changes caused by AD, they are often used to diagnose AD. Multimodal fusion based on these two types of images can effectively utilize complementary information and improve diagnostic performance. To avoid the computational complexity of the 3D image and expand training samples, this study designed an AD diagnosis framework based on a 2.5D convolutional neural network (CNN) to fuse multimodal data. First, MRI and PET were preprocessed with skull stripping and registration. After that, multiple 2.5D patches were extracted within the hippocampus regions from both MRI and PET. Then, we constructed a multimodal 2.5D CNN to integrate the multimodal information from MRI and PET patches. We also utilized a training strategy called branches pre-training to enhance the feature extraction ability of the 2.5D CNN by pre-training two branches with corresponding modalities individually. Finally, the results of patches are used to diagnose AD and progressive mild cognitive impairment (pMCI) patients from normal controls (NC). The experiments were conducted with the ADNI dataset, and accuracies of 92.89% and 84.07% were achieved in the AD vs. NC and pMCI vs. NC tasks. The results are much better than using single modality and indicate that the proposed multimodal 2.5D CNN could effectively integrate complementary information from multi-modality and yield a promising AD diagnosis performance.