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.

An efficient nature inspired algorithm based on particle swarm optimization (PSO) is presented in this paper for the optimal design of planar multi-layered radomes for multiband applications. Material layer sequence and thickness profile are the two critical factors determining the position of pass bands in the frequency range of operation as well as the transmission performance in those bands. These design aspects have to be appropriately optimized to achieve the desired performance, and it becomes a daunting task for radome designers when a comparatively large database of suitable materials is available in the solution space. Even though commercially available software packages provide options (like particle swarm optimization (PSO), genetic algorithm (GA) etc.) for the optimization of thickness profile, they do not have the functionality for optimizing the position of a specific material inside the multi-layered radome wall configuration. In this regard, the proposed PSO-based algorithm automatically chooses suitable materials from the predefined database and optimizes the thickness for each layer, in order to achieve superior transmission in user defined pass bands. Furthermore, the superiority of the indigenously developed algorithm over the optimization techniques available in full wave simulation software (FEKO) w.r.t. accuracy and computational efficiency is also established using suitable case studies and validations. Although PSO has been used in the context of radomes, its application for the simultaneous optimization of material layer sequence and thickness profile of multi-layered radomes is not reported in literature to the best of our knowledge.

There is complex electromagnetic interference in the substation. In order to improve detection accuracy, a digital lock-in amplifier is used in the detection of the grounding grid. This paper introduces the principle of non-destructive testing of grounding grid based on electromagnetic method. Firstly, the distribution characteristics of surface magnetic induction intensity at different frequencies are obtained by CDEGS simulation. At the same time, it describes the principle and structure of an orthogonal vector type digital lock-in amplifier in detail. In order to realize the high-precision grounding grid detection system, the hardware circuit of the digital lock-in amplifier is designed by FPGA and analog-to-digital converter. The digital lock-in amplifier algorithm is implemented in the FPGA. Finally, the digital lock-in amplifier is tested. The test results show that when the signal-to-noise ratio of the signal to be tested is -20 db, the signal amplitude measurement error is less than 3%. The designed digital lock-in amplifier is applied to the actual grounding grid detection, and the topology and corrosion of the grounding network can be detected. Therefore, the digital lock-in amplifier can be effectively applied to non-destructive testing of grounding grid.

The design of a wideband antenna using truncated corners partial ground plane loaded with L-shaped stubs and inverted T-shaped slots has been presented in this manuscript. The different concepts and structures related to antenna designing have been employed to attain the optimized model of antenna. L-shaped stubs and inverted T-shaped slots incised in the structure of antenna improve the impedance matching and bandwidth of proposed antenna. The fed 50Ω microstrip line has been applied to the proposed structure for attaining distinct performance parameters like reflection coefficient, gain and radiation pattern. The distinct structures of proposed antenna have been juxtaposed, and it is found that the structure with L-shaped stubs and inverted T-shaped slots shows improved antenna performance parameters. The designed antenna exhibits the bandwidth of 133.04% (3.14-15.62 GHz) and 16.96% (18.56-2.0 GHz) with improved reflection coefficient and gain. The proposed antenna has also been fabricated and tested for validation of simulated and measured results, and found in good agreement with each other. The design of proposed antenna is carved on a low cost thick substrate with compact electrical size of 0.566λ x 0.452λ x 0.0301λ mm³ at 5.45 GHz frequency and can be used for different wireless applications in the frequency range 3.14-15.62 GHz and 18.56-22.0 GHz.

A novel hybrid resonant structure is proposed to decouple a dual-band microstrip antenna array. The decoupling structure is composed of two H-shaped strips, and the lower and upper ones respectively collaborate with an X-shaped slot to reduce mutual coupling at 4.5 GHz and 5.5 GHz. Two sub-patches of different sizes share a connection feeding line to construct the dual-band array element, which is arranged along H-plane with the edge-to-edge spacing 0.15 λ_l and 0.24λ_h (λ_l and λ_h are the free-space wavelengths of 4.5 GHz and 5.5 GHz, respectively). Simulated and measured results indicate that through loading the hybrid resonant structure, 31.6dB and 24.0dB reductions of mutual coupling at two frequencies are obtained, while the levels of coupling coefficients are both below -30 dB in two operating bands. Moreover, the modified radiation patterns, improved diversity metrics and weakened coupled current distributions further verify its superior decoupling capability. The proposed decoupling structure reveals its promise in being employed in communication system and multielement linearly antenna arrays.

The coaxiality of the transmitter and receiver has a significant impact on the efficiency in a wireless power transfer system. In order to keep high system efficiency, a novel coil structure is studied in this paper. Several plane coils are crossed to make up a three-dimensional coil structure in the transmitter, which will make sure the system in the state of strong magnetic field coupling. In the theory part, the magnetic field equation of different relationships between transmitter and receiver is deducted in detail. In the simulation part, the performance of the three-dimensional coil structure has been studied. The simulation results show that the new coil structure can generate a rotating magnetic field, and the rotating magnetic field will keep the system in the state of the strong magnetic field coupling in the simulation model. In the experimental part, the three-dimensional coil structure has been compared to a plane coil structure. The experimental results show that the efficiency of the three-dimensional coil structure is increased above 10% in the misalignment situation. The simulated and experimental results show that the new three-dimensional coil structure has a better performance in the misalignment situation than the plane coil structure in a wireless power transfer system.

An elliptical array, composed of 10 uniform elliptical apertures as the radiating elements, is presented. Assume that each aperture in an electric conducting plane spreads on the elliptic orbit and is fed by the uniform plane wave in order to obtain a low SLL array pattern with high directivity, the elliptic orbit eccentricity and the angular position of each array element are stimulated. The applied parameters are determined by an elaborate optimization procedure. The utilized procedure, comprising the geometric computational technique (GCT), and angular positions excitation (APE) is stated in detail, respectively to determine a satisfactory eccentricity and the angular position of each element.

In this manuscript, the thermal effect on a lumped element balanced dual-band band-stop filter (BSF) has been discussed in detail for the first time. The response of a novel filter should maintain consistency over a wide range of temperature. Although any microwave filter in general is designed for room temperature condition, the filter is employed for applications where the operating temperature constantly changes. Therefore, it is necessary to check the reliability of the filter response within a specific temperature range based on its application. Modern simulation software helps to make an initial assumption about the filter performance at different thermal conditions before its lab testing or actual application. Here, a quantitative analysis has been provided to show how change in temperature contributes to the change in each component value of a lumped element filter. This analysis is followed by a simulation to show that a balanced lumped element filter exhibits lower loss than its single-ended counterpart. Also, as the temperature varies, the balanced design demonstrates less deviation in the loss value than a two-port design. Next, a balanced dual-band BSF prototype with center frequencies 1.151GHz and 1.366GHz (25℃)is characterized with a 4-port network analyzer under different temperature conditions. The experimental results exhibit a good match with the simulation results. For a variation of 80℃ in temperature, the maximum deviation obtained for the filter center frequency, absolute bandwidth (ABW) and insertion loss (Sdd21) are 5MHz, 2.8MHz and 2dB, respectively.