In this paper, we discuss the spectral property of radiation of an electron moving in a bi-period harmonic undulator field with a phase between the primary undulator field and the harmonic field component. We derive the expression for the photons per second per mrad² per 0.1% BW of the radiation. A small signal gain analysis is also discussed highlighting this feature of the radiation. A bi-period index parameter, i.e., Λ is introduced in the calculation. According to the value of the index parameter, the scheme can operate as one period or bi-period undulator. It is shown that when Λ = π, the device operates at the fundamental and the third harmonic. However, when Λ = π/2, it is possible to eliminate the third harmonic.

This paper describes an innovative technique for the quantitative reconstruction of the dielectric and conductivity distribution of objects in a microwave tomography framework using sparse data. The proposed method tries to extract information about the size, shape, localisation and dielectric distribution of various inclusions within the object under study using an iterative reconstruction methodology in the sparse domain. The proposed algorithm combines the Distorted Born Iteration method (DBIM) and a convex optimization technique for solving the inverse ill-posed problem. The Re-weighted Basis Pursuit (RwBP) algorithm is chosen as the convex optimization technique in this work. The performance of the proposed algorithm has been compared with the TV-norm method, and the results obtained are highly encouraging. The proposed method produces a significant reduction in the reconstruction error as compared to the TV norm method with an error value of 0.083 as against 0.32 in the case of TV norm in the presence of 25 dB noise. By accurately preserving the edges of the inclusions the proposed technique is found to provide an overall improvement in the reconstruction in terms of tissue differentiation (permittivity and conductivity), dimensions of inclusions, resolution, shape, size and coordinate localisation of inclusions. The proposed algorithm converges within 10-12 iterations as compared to other complex imaging algorithms available in the literature. Further, this proposed technique is validated using experimental data from an actual breast imaging setup. The three inclusions of 10 mm, 6 mm, and 3 mm have been localised with errors of 0.052, 0.04, and 0.09, respectively The results obtained from the real-time data show the applicability and feasibility of the proposed algorithm in breast tumor imaging application

Wearable antennas have received a great deal of popularity in recent years owing to their enticing characteristics and opportunities to realize lightweight, compact, low-cost, and versatile wireless communications and environments. These antennas must be conformal, and they must be built using lightweight materials and constructed in a low-profile configuration when mounted on various areas of the human body. These antennas ought to be able to function close to the human body with limited deterioration. These criteria render the layout of wearable antennas demanding, particularly when considering factors such as investigating the usability of textile substrates, high conductive materials during fabrication processes, and the effect of body binding scenarios on the performance of the design. Although there are minor differences in magnitude based on the implementations, several of these problems occur in the body-worn deployment sense. This study addresses the numerous problems and obstacles in the production of wearable antennas, their variety of materials, and the techniques of manufacturing alongside with bending scheme. This is accompanied by a summary of creative features and their respective approaches to address these problems recently raised by work in this area by the science community.

Microwave Imaging (MI) is a new technique for detecting breast cancer using electrical property difference between the non-malignant and malignant tissues present in the breast. Numerous studies show that detecting the depth of the tumor is the essential measure in determining additional management. Developing evidence in many of the literature surveys illustrate that detecting tumor depth is a precise parameter for identifying the affected area. Thus, Ground Penetrating Radar (GPR) algorithm is applied successfully to detect the exact depth of the malignant tissue. Generally, GPR is originally conceived for archaeological investigations, building condition assessment, detection of buried mines, etc. But here an effort has been made to apply GPR to Radar-based breast cancer detection. The simulated bandwidth of the proposed UWB antenna starts at 2.4GHz and ends at 4.7 GHz. The electromagnetic wave reflected due to dielectric property variation is used by GPR algorithm to identify the depth of the tumor. Before applying a depth migration technique, preprocessing steps like Cartesian form transformation, Hermitian Signal Processing, and Inverse Fast Fourier Transform (IFFT) have to be followed in the backscattered signal to convert positive frequency data into time-domain data. Depth details can be noticed in the migrated image, after applying the migration procedure. Results show that GPR algorithm can be effectively used for detecting the tumor embedded in the depth of the breast tissue. To understand the effectiveness of this imaging scheme, an experimental analysis is done using a combination of wheat flour and water-petroleum jelly. The measured impedance bandwidth of the UWB antenna ranges from 2.8 GHz to 4.48 GHz. The observation is done for a known spherical tumor of diameter 13mm which is placed at different depths from the skin layer. While applying the algorithm in the received backscattered signal, we were able to detect correctly the tumor at a depth of 45mm embedded in the breast tissue. The experimental results are compared with simulation ones to validate the aptness of a microwave imaging approach for detecting the depth of the tumor.

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.