The design of a compact stubbed microstrip balun with very wide range higher order harmonic suppression, is presented based on multiple open stub units, for which advantages are twofold, compared to single and double open-stub based designs. First, the high degree of size and harmonic reduction is achieved within the realizable impedance values. Second, the achieved bandwidths are fairly large (close to those of conventional balun) for a given set of electrical lengths. Unlike other methods, here, predetermined bandwidth analysis is provided for various levels of size and harmonic reduction. A prototype balun, having 75% size reduction and simultaneous wide higher order harmonic suppression extended up to 12f₀, while maintaining good input matching, amplitude and phase balance bandwidths, is fabricated for validation.

This article deals with the generalized procedure of designing and optimizing multi-ring radial and thrust permanent magnet bearings (PMBs) with an axial air gap for maximum force and stiffness per volume of the magnet. Initially, the procedure of determining optimized design variables in both the configurations is presented using the MATLAB codes written for solving the three dimensional (3D) equations of force and stiffness in PMB having `n' number of rings on the stator and rotor. The maximized results of the forces in both radial and thrust multi-ring PMBs are validated with the values obtained using finite element analysis (FEA). Then, the correlation between the optimized parameters and the air gap is obtained, and curve fit equations for the same are proposed in terms of stator outer diameter. Further, curve fit equations establishing the relationship between the maximized bearing features, and the aspect ratio (L/D4) of the bearing are expressed for different values of air gap in both the radial and thrust bearings. Finally, the generalized method of designing and optimizing the multi-ring PMB is demonstrated with a specific application. A designer can use the presented curve fit equations for optimizing design variables and calculating maximized bearing features in multi-ring radial and thrust PMBs easily just by knowing the bearing features for a single ring pair.

In this research work a compact patch antenna which is reconfigurable for frequency is presented. Frequency reconfigurability is achieved by the use of two PIN diodes. Antenna operates over four frequencies, i.e., for WiMax (4.94 GHz), WLAN (5.35), and C-Band (6.25 and 6.83 GHz) applications. The overall dimension of antenna is 25×25 mm², and an FR-4 substrate having dielectric constant of 4.4 and thickness 1.6 mm is used to fabricate the prototype of the proposed antenna. Different resonant frequencies are obtained by cutting a ∏-slot and a U-slot in radiating patch and by modifying ground slot with a modified slotted structure. One diode is used in ground, and another PIN diode is used on the patch at an appropriate position. Maximum gain of 3.91 dBi and stable radiation characteristics and VSWR < 2 are obtained at the operating bands in simulation and measurement. The antenna elicits its novelty through compactness, portability for communication devices through combination of only two PIN diode switching in cellphones, tablets PCs, and other satellite communication devices operating in C-band as per FCC standard. A prototype of antenna is fabricated, and the measured and simulated parameters are in good agreement.

In coaxial magnetic gear (CMG), magnetic modul ation ring is composed of a modulator and a connecting bridge. The torque performance of the magnetic gear are affected by the different structures of the magnetic modulation ring. In this paper, fifteen different kinds of magnetic modulation rings with different structures are proposed; they consist of three different shapes of modulators and five different locations of connection bridges. By using the two-dimensional finite element method (FEM), the magnetic flux density, magnetic line distribution, static torque, and steady-state torque of the CMG with different structures of magnetic modulation ring are analyzed. The results show that the innermost bridge has the least effect on the torque and torque ripple of the CMG, while the outermost bridge has the opposite effect. The torque capacity of the circular modulator and arc modulator is higher than that of the square modulator, and the circular modulator helps to reduce the inner torque ripple, while the square modulator helps to reduce the outer torque ripple. This paper can provide some references for the design of the magnetic modulation ring.

A planar I-shaped folded-patch antenna with a footprint of 21 mm x 21 mm x 1.6 mm is designed for compact UHF RFID tags to cohere on metal. The antenna consists of three parts: a square ground plane, an I-shaped patch and a ring resonator. The I-shaped patch is interconnected to the ground plane through a narrow shorting stub, and the microstrip feed line is inserted into the patch to reduce the input impedance of the patch. Extra capacitance and inductance introduced by the ring resonator can lower the tag's resonant frequency down to the expected UHF RFID band. The proposed antenna is manufactured, and there is excellent consistency between simulation and measurement results. The proposed tag antenna achieves a far read distance up to 6.3 m on metal (with 4 W equivalent isotropic radiated power) at resonant frequency of 920 MHz.

Magnetic micro-robots are used widely in a narrow space, such as internal inspections and desilting of slender pipelines, minimal- or non-invasive diagnoses and treatments of various human diseases in blood vessels, and micro-manipulations, micro-sensing fields. Magnetic micro-robots are usually driven by several electromagnetic coils. It is essential to understand the magnetic field and magnetic forces acting on micro-robots to drive the magnetic micro-robots more effectively. In this paper, the finite element method is applied to simulate the magnetic field generated by a coil assembly. Moreover, a three-dimensional magnetic force simulation is also performed to reveal the magnetic forces acting on a cylindrical magnetic micro-robot. Experimental measurements validate the simulated results. A Hall sensor is used to measure the magnetic field along the coil assembly's axial and radial direction. The micro-robot is glued to a connecting rod, fixing a force sensor to measure the magnetic forces acting on it. The measured results are in good accordance with the simulated ones, which prove the validity of the simulation. The results from this study show potential to provide a reference to magnetic micro-robot applications.

Compressed sensing (CS) imaging radar can obtain higher resolution than the traditional synthetic aperture radar (SAR) with less data, which makes it important for military and civilian applications. However, noise, especially active noise jamming will degrade its performance. This paper describes the signal model of the CS imaging radar under noise jamming. Through theoretical analysis and simulation experiments, the influences of different jamming patterns, jamming parameters and reconstruction algorithms on the performance of CS imaging are compared. It can provide reference for the research of anti-jamming technology of CS imaging radar.

A Ku-band long linear helical subarray (LLHS) for a high-power cylindrical conformal array antenna has been developed. The LLHS consists of 80 helical antennas can be used to constitute conformal array of cylindrical surface. Through the research on the embedded probe structure, the adjustment of the coupling ability of different types of unit probes and the sealing method of the whole feeding, the problems of large feed reflection, the uneven coupling amount of the unit probe in the rectangular waveguide system are solved, and the LLHS which can be used in the high-power conformal array is realized. The LLHS which is 52.35λ length can obtain 25.2 dB gain, 2.31 dB axis ratio, 90% aperture efficiency, -15.65 dB reflection at 12.5 GHz, and the reflection is lower than -14 dB during 12-13 dB. In addition, it could handle a pulse power of 166 MW under vacuum condition.

Radio frequency (RF) energy harvesting technologies have attracted different efforts from researchers to employ low energy in powering portable electronic devices. In this article, an Ultra-Wide Band (UWB) antenna based on a Vivaldi fractal antenna backed with a Metamaterial (MTM) array is exemplified for RF-energy harvesting in the modern 5G networks. The antenna is connected to a full wave rectifier circuit to obtain a rectified DC current. It is found that the exemplified antenna provides a maximum output voltage of 1.4V and 1.3 V at 3.1 GHz and 4 GHz, respectively, when the incident RF power is around 17 Bm. The measured results and simulations show excellent agreement. The antenna is printed a flexible Kodak photo paper of 0.5 mm thickness with ε_r = 2 and loss tangent of 0.0015. The numerical simulations are conducted using CST MWS and HFSS software packages. The proposed antenna structure is fabricated using an ink jet printing technology based on conductive silver nanoparticle ink. Finally, from the obtained measurements after the comparison to their simulations, the proposed antenna is covers the frequency band from 2.4 GHz up to 20 GHz with a gain of 1.8 dBi at 3.1 GHz and 4 dBi at 4 GHz.

A novel dual-band frequency selective surface (FSS) operating at Ku- and Ka- bands is presented in this paper. The proposed FSS is an aperture element constituted by a square loop loaded with four symmetrical umbrella-shaped stubs on the front side of the dielectric substrate. A good angular stability up to 60° angle of incidence for both TE and TM polarizations is provided by the FSS. Moreover, the two passbands of FSS can be controlled independently and flexibly by changing corresponding structural parameters. A prototype of the FSS is fabricated and measured. The good agreement between simulation and measurement results further proves the performance of the FSS.

A CPW (coplanar waveguide) bandpass filter based on spiral-shaped DGSs (defected ground structures) which can be used in the 5G band is proposed. Two pairs of face-to-face symmetrical spiral-shaped DGSs are added to the ground planes of a CPW main transmission line. A cross-shaped notch is adopted in the central strip of the CPW main transmission line to generate the passband, while two m-shaped DGSs are brought in to improve the passband performance of the filter. The measured results show that the central frequency is 3.54 GHz, and the 3-dB bandwidth is from 3.29 GHz to 3.79 GHz. The filter has a 10.1% bandwidth with a return loss better than 10 dB from 3.35 GHz to 3.71 GHz, and the insertion loss is less than 2.0 dB in the passband. Besides, there are two transmission zeros near the passband at 2.45 GHz and 4.81 GHz, which can improve the stopband rejection.

We firstly derived the simplified formulas for calculating attenuation constants of surface wave in double-layer magnetic absorbing sheets (MASs). The fabricated two kinds of magnetic absorbing sheets, having advantages in the low and high frequency range respectively, were used to design a group of 0.5 mm-thick double-layer sheets. Numerical calculation results show that the surface wave attenuation constants of double-layer absorbing sheet with a proper combination of the two MASs can be significantly enhanced in the whole frequency range, compared to those single-layer sheets of the same thickness. Furthermore, the simulations of mono-static RCS reduction of the metal slab coated with double-layer MAS well confirm the calculation analysis. This work demonstrates that it is feasible for double-layer magnetic absorbing sheet to enhance the surface wave attenuation ability and broaden application frequency range.

A method is proposed to calibrate a planar phased array by reconstructing its aperture distribution, in which the aperture distribution is superposed within the physical range of radiating element. Consequently, the calibration coefficients are solved for the linear relationship between the superposed aperture distribution and elements' excitations. The calibration accuracy that is influenced by resolution of aperture distribution is also discussed in this paper. In practice, the reconstruction procedure of aperture distribution is based on the plane wave spectrum (PWS) theory, utilizing FFT and IFFT techniques. This method turns out to be valid by experiment.

In this article, a new approach has been demonstrated for the bandwidth enlargement of a substrate integrated waveguide (SIW) cavity-backed antenna. The proposed structure employs bilateral slots, instead of unilateral slots, which is a distinct approach, in contrast to traditional cavity antennas. The proposed antenna embodies SIW cavity with a height less than 0.017λ₀ and thus holds low-profile planar geometry, while retaining lower losses and light weight. The non-resonant slot, at the bottom plate, produces two-hybrid modes (odd TE₂₁₀ and even TE₂₁₀). The quality factor (Q) of these hybrid modes is greatly reduced by loading the resonant slot cut at the top metallic plate of the SIW cavity which leads to achieving a wideband response. A sample is fabricated and investigated at X-band. It is shown that the experimental results are well-matched with the simulated ones. The measured impedance bandwidth of the proposed antenna is 860 MHz (8.6%). Moreover, it renders a maximum gain of 6.56 dBi at 9.78 GHz and 6.75 dBi at 10.35 GHz, within the operating bandwidth. The cross-polarization radiation levels of maximum -26 dB and -28 dB are obtained at the corresponding resonant frequencies, respectively.

To obtain three-dimensional (3-D) high-precision and real-time through-wall location under ambiguous wall parameters, an approach based on the extreme learning machine (ELM) which is a neural network is proposed. The wall's ambiguity and propagation effects are both included in the hidden layer feedforward network, and then the through-wall location problem is converted to a regression problem. The relationship between the scattered signals and the target properties are determined after the training process. Then the target properties are estimated using the ELM approach. Numerical results demonstrate good performance in terms of effectiveness, generalization, and robustness, especially for the kernel extreme learning machine (KELM) approach. Noiseless and noisy measurements are performed to further demonstrate that the approach can provide good performance in terms of stability and reliability. The location time, including the training time and the test time, is also discussed, and the results show that the KELM approach is very suitable for real-time location problems. Compared to the machine learning approach, the KELM approach is better not only in the aspect of accuracy but also in location time.

In this letter, a multiband compact low-profile planar antenna based on multiple resonant stubs is proposed and studied. By utilizing two pairs of stubs embedded on a defected ground, the reflection coefficient less than -10 dB can be achieved with broadband characteristic for applications of wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX). Meanwhile, a pair of inserted slots on both sides of a curve slot is applied to the antenna design, which decreases the cross polarization. A multiband antenna is fabricated and measured to verify the design. The antenna is compact with operation frequencies for WLAN (2.45/5.2/5.8 GHz) and WiMAX (2.8/3.8/5.5 GHz) applications. The measured peak gains are 5.5, 4.4, 0.0, and 5.6 dBi at 2.45, 2.8, 3.8, and 5.5 GHz, respectively.

This paper presents a new multi-band stopband filter loaded by a shorted metamaterial circuit. Firstly, two filters loaded by stubs and open ring resonators (ORRs) are studied and compared. The ORRs allow more effects in terms of miniaturization by a shifting toward low frequencies and rejection bandwidth (57.34%). To improve the filter efficiency, coupled split ring resonators (SRRs) are used. The final filter is characterized by a miniaturized size of 18.8 x 40 mm², wide rejection bandwidth, high selectivity level and multiple resonances over S, C, X and Ku bands. L-C equivalent circuit model filter and other characteristics are investigated. A prototype of the filter with coupled SRRs has been fabricated and measured. Good matching among EM-simulation, equivalent circuit modelling, and measured results are achieved.

In this paper, we develop numerical methods for using vector spherical and spheroidal waves in the hybrid method to calculate the multiple scattering of objects of complex shapes, based on the rigorous solutions of Maxwell equations in the form of Foldy-Lax multiple scattering equations (FL). The steps in the hybrid method are: (1) calculating the T-matrix of each single object using vector spherical/spheroidal waves and (2) vector spherical/spheroidal waves addition theorem. We utilize the commercial software HFSS to calculate the scattered fields of a complex object on the circumscribing sphere or spheroid for multiple incidences and polarizations. The T-matrix of spherical waves or spheroidal waves are then obtained from these scattered fields. To perform wave transformations (i.e. addition theorem) for vector spherical/spheroidal waves, we develop robust numerical methods. Numerical results are illustrated for T-matrices and numerical vector addition theorems.

Potential-based integral equations are being explored to develop numerical methods that avoid low frequency breakdown issues and are better suited to couple to quantum physics computations. Important classes of quantum electrodynamics problems are typically formulated in the radiation gauge, leading to interest in efficient numerical solutions able to be performed directly in this gauge. This work presents time domain integral equations for penetrable regions that are developed in the radiation gauge. An appropriate marching-on-in-time discretization scheme is developed that fully conforms to the spatial and temporal Sobolev space properties of the integral equations. It is shown that following this approach leads to a discrete system with improved stability properties that produces accurate results down to very low frequencies. The accuracy and stability of this formulation at low frequencies are shown through numerical results.

A new design for a cylindrical dielectric resonator antenna (DRA) with a capability of switching between circular, linear horizontal and linear vertical polarizations is introduced. The DRA, operating at the center frequency of 3.25 GHz, is fed by a microstrip line through two dog-bone slots. In this design, only two PIN diodes are employed as switching elements which significantly decreases the complexity of DC biasing circuits compared to existing designs. The PIN diodes are embedded in transformers connected to the feeding microstrip lines. This technique conveniently allows to make compensations for parasitic effects of the PIN diodes junction capacitors on the antenna matching bandwidth. The circular, linear horizontal and linear vertical polarizations have a bandwidth of 22%, 17% and 18%, respectively. The 3-dB axial ratio bandwidth for the circular polarization is 12%. The measured results obtained from prototyped antenna agree well with simulated results of the designed antenna system, which confirms the validity of the design process.