In this paper, we extend our previously published hybrid analytical model for estimation of shielding effectiveness of a dual-cavity structure with an aperture array to generalize the model for a wider range of applications. The aperture array in the center and off-center, higher order modes, and multi-cavity are taken into consideration, respectively. At last, comparations of the results calculated by the extended hybrid analytical model with those obtained by the simulation software CST are given. The results show that the extended hybrid analytical model for shielding effectiveness prediction of a three-cavity structure with numerous apertures has high precision and high efficiency.

Stub-loaded step-impedance resonator (SLSIR) is a multi-mode resonator and can be applied to implement multi-band or wideband filters. In this paper, odd- and even mode impedance analysis is used to resonant properties of the SLSIR. Only two SLSIRs are applied to design a quint-band bandpass filter (BPF). To find the required five resonant modes, the frequency ratios of the high order modes to the fundamental mode of the SLSIR are calculated depending on the impedance ratio and the length ratio of the SLSIR. Several coupling types of the SLSIRs are considered first to have enough energy for all the five passbands. When forming the quint-band, a pair of the SLSIR are coupled electrically and connected with 0o feeding input/output structure. The center frequencies are designed at 1.38 GHz, 2.58 GHz, 3.69 GHz, 5.36 GHz, and 5.8 GHz, corresponding to the different communication applications. The filter is designed, fabricated, and measured. Simulated and experimental results are in agreement, verifying the design concept.

Different optimization strategies to reduce the earth resistance in a high resistivity soil are discussed in this work and illustrated with a practical example. Finite Element simulations reproducing real-world conditions in terms of structure design and soil profiles have been made to evaluate the improvements that should be adopted to minimize earth resistance. We analyze an example of an earthing system of an array of four identical telescopes installed on high resistivity (k­¢m order) soils with two different behaviors. In the first one, current dissipation occurs in an uniform soil. In the second one, a terrain with four layers of different resistivities is considered. This situation corresponds to a real world case of an observatory constructed in a volcanic terrain. It was found that the best strategy in each case differs: extend horizontal electrodes as far as possible from the foundation in the first case and combine these electrodes with buried vertical electrodes that connect with deep high conductive layers in the second. The results are discussed in terms of the achieved improvements depending on the modifications introduced in the main structure.

An eight-element ultra-wideband multiple-input multiple-output antenna system is proposed for the 5G mobile terminals. Each radiating branch is composed of a Loop and a monopole antenna. The ultra-wideband characteristics of the antenna are obtained by a T-shaped feed branch coupling a radiation branch. Furthermore, the isolation is lower than -15 dB by introducing a T-shaped neutralization line structure. The results of simulation and measurement show that the antenna system can cover 3.3-5.6 GHz, and the antenna efficiency is 45%-80%. At the same time, the envelope correlation coefficient between any two elements is lower than 0.03. Therefore,the proposed antenna in this study is very suitable for the eight-element MIMO antenna system as a reference.

This study presents a triple resonance microstrip slotted antenna element for 5G (5.15-5.875 Wi-Fi band) applications. This antenna constitutes a rectangular patch stimulated with an I-shaped slot and two shorted metallic vias. This arrangement results in an enhancement of the bandwidth. The antenna features a wide impedance bandwidth (IBW) matching due to triple resonances when being properly excited by coax-probe feed. The IBW of the antenna ranges from 5-6 GHz band with three resonances at around 5.2, 5.5, and 5.8 GHz. Finally, the antenna is fabricated and measured, which displays a -10 dB IBW of 5.04-6.05 GHz (18.2%) featuring stable radiation and gain (around 7 dBi). Moreover, the measurements are in good agreement with simulations. On the account of the single-layered dielectric, this antenna can be easily mounted with active electronics.

In this paper, a plasmonic sensor based on a metal-insulator-metal (MIM) waveguide with a slotted side-coupled elliptical cavity is proposed. The transmission characteristics of the cavity are analyzed theoretically, and the improvements of performance for the elliptical cavity structure compared to a single disk cavity are studied. The influence of structural parameters on the transmission spectra and sensing performances is investigated thoroughly. The achieved sensitivity for the first mode was S = 959 nm/RIU and S = 2380 nm/RIU for the second one. Its corresponding sensing resolution is 1.04 x 10^-5RIU for mode 1 and 4.20 x 10^-6RIU for mode 2, respectively, and high transmissions are achieved at the two resonant wavelengths of 898.8 nm and 1857.1 nm. The proposed plasmonic sensor is a good candidate for designing novel devices and applications, in the field of chemical and biological sensing, and also in the field of plasmonic filters, switches, etc.

Analytical solution and numerical results are provided for the problem of plane wave scattering by an electrically large Perfect Electric Conductor plate located vertically over a simple lossy dielectric half-space. The incoming monochromatic homogeneous plane wave is assumed to be incident from an arbitrary direction and decomposed into TE and TM components. Physical Optics approximation is used for estimating the currents induced on the plate. The scattered fields are obtained explicitly by evaluating the Electric Field Integral Equation analytically incorporating the set of Green functions by R.W.P. King which apply under High Contrast Approximation. Amplitude and phase variations of the numerical distance and attenuation function are illustrated in HF-MW band ranges. Azimuth and elevation patterns for total scattered electric fields are illustrated with emphasis on the relative contributions of surface wave fields depending on operating frequency and refractivity. An analytical procedure to extract free space RCS information from measured/calculated data is introduced based on the asymptotic behaviours of surface waves and its stability is tested numerically.

Microwave radiometer is a high-sensitivity ``camera'', which realizes high-resolution imaging by receiving the natural radiation signal in microwave band from the observation scene. Due to the imperfection of the system hardware, the measured data include not only the radiated signal of interest but also the noise generated by the system hardware itself. These unexpected noises will affect the imaging performance of the system, especially for the synthetic aperture interferometric radiometer (SAIR). In this paper, the noise behavior of the SAIR system is analyzed and modeled for the first time. Based on the noise behavior model, a method is proposed to pick the optimal averaging time for imaging with high fidelity in the SAIR system. Some experiments are carried out to verify the correctness of the noise behavior model and the optimal averaging time picking method for SAIR. With the noise behavior model and the optimal averaging time picking method, it can provide an effective guide for the SAIR system design, error correction, and reconstruction.

A new ring wideband bandstop filter (BSF) and its exact design method is proposed and investigated in this letter. The BSF is devised by introducing an additional transmission line to a traditional hairpin bandstop filter in parallel, hence giving enhanced selectivity and attenuation performance. A lumped lowpass equivalent circuit is introduced to explain the mechanism of the filter. Rigorous correspondence between the BSF and its equivalent circuit is established by comparing their even- and odd-mode input admittances. This enables the BSF to be synthesized the same way as lumped filters. Both the BSF and the method have been documented by a design example.

Compressive sensing (CS) is an effective method for reconstructing magnetic resonance imaging (MRI) image from under-determined linear system (ULS). However, how to improve the accuracy of MRI image reconstructed by CS is still a serious problem, especially in noisy conditions. To solve this problem, in this paper, we propose a novel approach, dubbed as regularized maximum entropy function (RMEF) minimization algorithm. Specifically, motivated by the entropy function in information theory, we propose a maximum entropy function (MEF) to approximate L_q-norm (0 < q < 1) as sparsity promoting objectives, and then the regularization mechanism for improving the de-noising performance is adopted. Combining the above two ideas, a new objective function of RMEF method is proposed, and the global minimum is iteratively solved. We further analyze the convergence to verify the robustness of the RMEF algorithm. Experiments demonstrate the state-of-the-art performances of the proposed RMEF algorithm and show that the RMEF achieves higher PSNR and SSIM than other widely-adopted methods in MRI image recovery.

A triple band notch MIMO/Diversity antenna using Inductance Boosted Compact Electromagnetic Band Gap (IB-CEBG) cells is presented in this paper. For obtaining compactness in the conventional EBG cell, spiral shaped defects are introduced. The proposed antenna obtains triple band notches in WiMAX (3.3-3.6 GHz), WLAN (5-6 GHz), and the X-band satellite communication (7.2-8.4 GHz) bands. IB-CEBG cells exhibits miniaturization of approximately 46% for WiMAX band, 50% for WLAN band and 48% for X-band Satellite communication band, compared to conventional EBG cells. To enhance the isolation among all four compact UWB monopoles, rectangular slots in the ground plane and parasitic decoupling arrangement are utilised. Further, a stepped structure with an angular separation of 90˚ is incorporated with individual monopoles to reduce mutual coupling effects. Stepped structure also helps in the better impedance matching by incrementing the path length. The results show that the magnitude of transmission coefficient is greater than 15 dB in between the ports of proposed antenna elements. Envelope Correlation Coefficient is less than 0.5, which lies in tolerable limits for Ultra-Wide band (UWB) frequency range. It has been noticed that notched frequency is dependent on IB-CEBG cell parameters. The proposed antenna is fabricated using an FR-4 substrate with overall dimensions of 58 x 90 x 1.6 mm³.

Using the moment method, we analyze a loop antenna with a perturbation segment in the presence of a ground plane. First, the radiation characteristics versus loop height above the ground plane are investigated. It is found that as the loop height increases to more than 0.2 wavelengths a novel antenna other than a conventional one can exist, showing an enlarged bandwidth of 9% for a 3 dB axial-ratio criterion. Next, the radiation mechanism of the novel antenna is compared with that of the conventional one. Last, the novel loop is used in a comb-line antenna as a radiation element. It is found that the CP wave bandwidth is five times as wide as that of a conventional comb-line antenna. The analysis results are verified by experimental work.

Rigorous quantum formulation of the Parity-Time (PT) symmetry phenomenon in the RF/microwave regime for a pair of coupled coil resonators with lump elements has been presented. The coil resonator is described by the lump-element model that consists of an inductor (L), a resistor (R) and a capacitor (C). Rigorous quantum Hamiltonian for the coupled LRC coil resonators system has been derived through twice basis transforms of the original basis. The first basis transform rotates the original basis such that off-diagonal terms of the governing matrix of the equation system of the coupled coil resonators is reduced to constants. Then a second basis transform obtains the quantum Hamiltonian, including the diagonal effective complex frequencies and off-diagonal coupling terms, together with the transformed basis. With the obtained quantum Hamiltonian, the eigenvalues and eigenvectors of the coupled coil resonators can be obtained as usual as the quantum Hamiltonian. Finally, numerical simulation verifies the correctness of the theory. The quantum formulation of the coupled coil resonators can provide better guideline to design a better PT-symmetric system.

This work aims at completing the Wiener-Hopf analysis of a canonical problem referring to an extra-ordinary transverse electromagnetic wave propagating within a parallel plane waveguide loaded with magnetized plasma when incident normally at the truncated edge of its upper conductor. The complicated mathematical issues faced herein comes from the non-symmetric Kernel functions involved in the related integral equation. This property puts two challenging issues, first the rarely occurring factorization of non-symmetric Kernels and secondly the handling of unidirectional surface and leaky waves. Although the formulation of the Wiener-Hopf equations was carried out in our previous work, these two challenges were not confronted, since that work has been completed only in regard to the closed-shielded geometry which involves a symmetric Kernel. Thus, the novel contribution of this work refers to completing the analysis of the open geometry by handling the factorization of the related non-symmetric Kernel, to evaluate the radiated field as well as to study the unidirectional waves for their near and far fields.

The finite-difference time-domain (FDTD) algorithm is a numerical stencil computation method, which is widely used in solving electromagnetic simulation problems. However, this algorithm is both computing and storage intensive, so the simulation efficiency is usually restricted in software implementation on CPUs. Recently, hardware accelerators have proved to be effective in improving the performance of various stencil computations. In this paper, we propose a hardware architecture of the 3D FDTD algorithm along with a practical convolutional perfectly matched layer (CPML) boundary condition and implement it on a field programmable gate array (FPGA). By applying the chain processing elements array and temporal parallel strategy, the proposed accelerator can achieve a maximum of 608 mega cells per second (Mcells/s), which is approximately 6 times higher than that of other reported designs on FPGAs. Moreover, the accelerator can maintain the speed above 467 Mcells/s for different grid sizes and CPML layers without modifying the hardware design, which demonstrates the performance stability and flexibility of the architecture under various applications.

Magnetic resonance electrical properties tomography has attracted attentions as an imaging modality for reconstructing the electrical properties (EPs), namely conductivity and permittivity, of biological tissues. Current reconstruction algorithms assume that EPs are locally homogeneous, which results in the so-called tissue transition-region artifact. We previously proposed a reconstruction algorithm based on a Dbar equation that governed electric fields. The representation formula of its solution was given by the generalized Cauchy formula. Although this method gives an explicit reconstruction formula of EPs when two-dimensional approximation holds, an iterative procedure is required to deal with three-dimensional problems, and the convergence of this method is not guaranteed. In this paper, we extend our previous method to derive an explicit reconstruction formula of EPs that is effective even when the magnetic field and EPs vary along the body axis. The proposed method solves a linear system of equation derived from the generalized Cauchy formula using the conjugate gradient method with fast Fourier transform algorithm instead of directly performing a forward calculation, as was done in our previous method. Numerical simulations with cylinder and human-head models and phantom experiments show that the proposed method can reconstruct EPs precisely without iteration even in the three-dimensional case.

Placing microwave absorbing materials into a high-quality factor resonant cavity may in general reduce the large interior electromagnetic fields excited under external illumination. In this paper, we aim to combine two analytical models we previously developed: 1) an unmatched formulation for frequencies below the slot resonance to model shielding effectiveness versus frequency; and 2) a perturbation model approach to estimate the quality factor of cavities in the presence of absorbers. The resulting model realizes a toolkit with which design guidelines of the absorber's properties and location can be optimized over a frequency band. Analytic predictions of shielding effectiveness for three transverse magnetic modes for various locations of the absorber placed on the inside cavity wall show good agreement with both full-wave simulations and experiments, and validate the proposed model. This analysis opens new avenues for specialized ways to mitigate harmful fields within cavities.

In this paper, a hybrid antenna array for 4G/5G smartphone applications is presented. The hybrid antenna system is composed of one array of two antenna elements for 4G application and another array of six antenna elements for 5G application. By loading PIN diodes and changing the on/off state of the PIN switch, then the resonance point will shift. The 2-antenna array broadens the bandwidth of 4G frequency band and is capable of covering GSM850/900/DCS1800/PCS1900/UMTS2100 and LTE2300/2500 operating bands. A U-shape monopole strip and an S-shape slot coupling technologies are also introduced, the 6-antenna array improves the impedance matching for the proposed 5G antenna array, and is capable of covering the 5G (3300 3600 MHz and 4800 5000 MHz), which can meet the demand of 5G application. Spatial and polarization diversity techniques are implemented on these antenna elements so that high isolation can be achieved. This hybrid antenna array is fabricated, and typically experimental results such as S11, isolation, radiation pattern, efficiency, and channel capacity are presented. The measured results are in good agreement with the simulated ones.

In this article, a modified circular shape printed dipole structure is studied to achieve wide bandwidth and dual-band circular polarization (CP) behavior along with dual polarizations. The idea behind this structure is that asymmetric geometry can give rise to circular polarization with an optimized position of coaxial probe feed. The circular patches on both sides of the substrate are altered with elliptical slots at an optimized location in association with opening slots. With these alterations the impedance bandwidth for S₁₁<-10 dB is ranging from 2.36-7.34 GHz (4.97 GHz) which is nearly 102.5% about mid-point frequency 4.85 GHz. The antenna resonates at a lower band (1.55 GHz) and shows linear polarization (LP) operation at that band whereas dual CP bands with dual senses are obtained at higher frequency ranges 4.00-4.60 GHz and 6.07-7.13 GHz respectively with 3-dB axial ratio bandwidth of 13.7% and 16.6%. The simulated and measured experimental results are in close agreement. This antenna is suitable to be used for navigation purposes, radar communication, and wireless communication (especially wireless avionics intra communications) in S and C bands, respectively.

First of all we inform the audiences that this article is a Review Paper (RP) for the PIERS17 Proceedings Paper (Zheng et al. [17]). The reason why we publish this RP is that: although the paper [17] reported important ideas and simulation facts, details of the contents were insufficient, and the audiences of the report were not satisfied. This was because the page number was limited, and we saved the number of pages. However, because the contents of~[17] are important, we decided to publish an RP, which would provide additional explanations or give considerations supporting main issues. Now, we start the abstract from Section~1. Here, we mention historical topics and RP-related things. In Section~2, we explain the problem of diffraction by a conically-mounted metal grating. To save the page number, we skip the method of solution. In Section~3, we explain our method in noise free case. We show the high precision of the quadratic (or parabola) approximation. We define the workspace (WS: relation between index range of a sample and a proper azimuth angle) and one-to-one correspondence between sample index and resonance angle. In Section~4, we try our method in a noisy environments. A curve-fitting procedure and three types of noise filters work to find satisfactory solutions. That is, in both 3. and 4., the resolution of the index is 7-digit usually, which is our target from the beginning. We think that the introduction of AI or statistical processing would increase the stability of the result. In Section~5, we mention some of future works. In APPENDIX A, we explain the method: How to find the azimuth angle, which we need in solving the diffraction problems by conically-mounted grating.