An efficient and stable hybrid method, based on the time-domain integral equation (TDIE) and time-domain physical optics (TDPO), is developed for investigating transient radiation and scattering from perfectly electrical conducting (PEC) objects. It at first requires partitioning the PEC object surface into TDIE and TDPO regions, respectively. Then, a set of hybrid TDIE-TDPO equations is derived and solved using an adaptive marching-on-in-order (MOO) method. The fast Fourier transforms (FFT)-based blocking scheme is further implemented into the proposed algorithm so as to reduce N²_O dependence of the traditional MOO method to N_Olog²(N_O), where N_O is the highest order of the weighted Laguerre polynomials used for computation. Under such circumstances, its computational cost, in comparison with the full TDIE-MOO solver, is reduced significantly. Several numerical examples are presented to demonstrate its accuracy and efficiency in solving some typical transient electromagnetic problems.

This paper presents a study of RF MEMS switch designed to be integrated in tunable filters for applications from W-frequency band to V-frequency band. Along the whole process, we go into detail of each procedure to present a complete study from design to fabrication and characterization of a RF-MEMS switch. The proposed concepts are validated by experimental results.

In this paper, a covariance matrix adaptation evolutionary strategy (CMA-ES) is employed for optimization design of non-uniform circular antenna arrays. To achieve minimum sidelobe levels with the constraint of a specific first null beamwidth, the CMA-ES is utilized to find out the optimal weights and geometry of the circular array. The three various circular ring arrays are solved via CMA-ES, and the results are presented for arrays of varying configurations. The design results obtained with CMA-ES are compared to the existing array designs in the literature and to those found by the other evolutionary algorithms. Comparison with the results of other algorithms reveals the superiority of the CMA-ES.

Wideband spectrum sensing is an essential functionality for cognitive radio networks. It enables cognitive radios to detect spectral holes over a wideband channel and to opportunistically use under-utilized frequency bands without causing harmful interference to primary networks. However, most of the work on wideband spectrum sensing presented in the literature employ the Nyquist sampling which requires very high sampling rates and acquisition costs. In this paper, a new wideband spectrum sensing algorithm based on compressed sensing theory is presented. The proposed method gives an effective sparse signal representation method for the wideband spectrum sensing problem. Thus, the presented method can effectively detect all spectral holes by finding the sparse coefficients. At the same time, the signal sampling rate and acquisition costs can be substantially reduced by using the compressive sampling technique. Simulation results testify the effectiveness of the proposed approach even in low signal-to-noise (SNR) cases.

We consider the problem of direction-of-arrival (DOA) estimation for distributed signals with electromagnetic vector sensors, of which each provides measurements of the complete electric and magnetic fields induced by electromagnetic (EM) signals. In this paper, we consider situations where the sources are distributed not only in space with a deterministic angular signal density，but also in polarization with partially polarized components. A distributed signals general model with electromagnetic vector-sensor array (EMVS-DIS) is established with some reasonable assumptions. Based on the EMVS-DIS model, the minimum-variance distortionless response (MVDR) estimators for distributed source DOA are derived. MVDR estimators do not require the knowledge of the effective dimension of the pseudosignal subspace. We compare our method with the distributed signal MUSIC-like estimator in electromagnetic vector-sensor arrays. The simulation studies show significant advantages in using the proposed EMVS-DIS model with electromagnetic vector sensors. Simulation results show that the new MVDR method outperforms the MUSIC-like algorithm by reducing the estimation RMSE and improving resolution performance for scenario with distributed sources. A robustness study of MVDR localizer was also conducted via simulations.

One novel dielectric conformal finite-difference time-domain (FDTD) method is proposed for computing specific absorption rate (SAR) distribution over the human body model in one metallic cabin with some windows on its wall. It is based on the concept of area average, which is different from other traditional conformal FDTD schemes. Our developed algorithm is verified by calculating both point and average SARs of dielectric sphere and human head models illuminated by an intentional electromagnetic pulse (IEMP), respectively, and CST Microwave Studio (MWS) also used for validating its accuracy. Numerical calculations are further performed to show the average SAR distribution over the human body model for different IEMP incidences, where the cabin door is opened or closed. The effects of E-field amplitude, direction and polarization of the incident IEMP on the SAR distributions are characterized in detail. We would like to say that this study will be useful for further electromagnetic protection for some persons working in high power radiation environment.

Aircraft skins manufactured from carbon fibre reinforced plastic (CFRP) can simultaneously support structural load and act as antennas. This offers the potential for disproportionately large antenna elements and arrays, and thus enhanced aircraft capability. The efficient design of such structures requires that the link between CFRP microstructure and electromagnetic performance be established. This paper presents a method of predicting the electromagnetic attenuation of waveguides manufactured from CFRP. The method considers both the orthotropic, complex conductivity of CFRP, high in the fibre direction and low transverse to it, and the local electric fields in waveguides, which vary with location and frequency. The method was validated experimentally using waveguides manufactured from aerospace grade IM7/977-3 prepreg tape with [0 90]s, [90 0]s and [±45]s ply stacking sequences.

We present an optical sampling technique that enables exploration of mismatches of a microstrip transmission line based on reflection analyses of electromagnetic pulses. The external electro-optic sampling scheme with a minute crystal detects high-speed electrical pulses over arbitrary locations of a line with very low-intrusiveness. The temporal pulsed signals measured with an on-wafer optical probing system and the corresponding spectra are obtained to analyze the transfer characteristics of a microstrip transmission line with 20 GHz bandwidth. The spectro-temporal response was cross-checked with commercial instruments. Applications of this optical probing technique to explore mismatches at the terminal port - based on both time and frequency domain reflectometry analyses - are also presented.

In this paper, a synthesis method is presented for Chebyshev type II band-pass filters in the microwave frequency range. We investigate the cause of the second harmonic passband of coupled-serial-shunted lines bandpass filters. Filters are employed substrate suspension, wavy-edge coupling, ring resonators, defect ground structure (DGS), and a combination of the wavy-edge coupling and ring resonators may be used and were investigated to suppress the harmonic pass-band. With a combination of the wavy-edge coupled-lines and ring resonators, the harmonic pass-band of the parallel-coupled line filter is rejected more effectively. Several filters are fabricated and measured to demonstrate the design.

Magnetic induction tomography (MIT) is a contactless measurement technique of biological tissue conductivity. In this study, the differential induced voltage equations are shown in single layer and n layers models. The paper describes a 16 channels MIT measurement system with working frequency of 1MHz, which can image the plan of low conductivity object. According to physical experiments, the sensitivity is about 0.29°/S·m^-1, and the maximum shift of the phase noise is 0.08°. Some preliminary clinical experiments were done, including 2 cases of meningitis and 5 cases of brain normal patients. The comparison of all the measured values shows that all values are smaller than 1.7° in the brain normal cases, but the values of meningitis cases are more than 2°, higher than those of brain normal patients. Therefore, the MIT measurement system has great application prospect in dynamically monitoring the brain diseases.

In this paper, the subaperture approximation (SA) method for 3-D microwave imaging is presented based on the sparsity of 3-D image. The idea is that the sparsity information can be extracted from the lower resolution image obtained using the subaperture of the (virtual) array and be used for high-resolution imaging to reduce the imaging region. Thus, a recursion procedure that can significantly reduce the computational cost is established. Compared with the surface-tracing-based method, the SA method can avoid the loss of isolated scatterers. The feasibility is verified by using experimental data. After analysis, the SA method can reduce the computational cost from two aspects: reducing the array element number needed to be processed and the pixels needed to be processed. The computational cost is mainly related to the target characteristics (the sparsity ratio and the topological structure), and decreases with the increase of the sparsity ratio. When the sparsity ratio is larger than 97.6%, the computational cost can be lower than 10% of the 3-D back-projection (BP) method.

An efficient strategy for reducing the signature of an antenna is to substitute the conventional solid ground plane with a patterned ground plane thus letting the incoming energy to pass through the structure except over the operating band of the antenna. However, in a real environment, the energy flowing through the FSS (Frequency Selective Surface) can be intercepted by eventual scatterers located behind the antenna, so to nullify the RCS (Radar Cross Section) reduction. To overcome this drawback, a novel composite structure is proposed which is able to dissipate such energy by placing a thin absorbing layer below the FSS ground. It is shown that a careful analysis has to be performed to accomplish this goal since the transparent antenna array and the backing absorber strongly interact and thus they cannot be separately designed. The optimal value of the foam spacer thickness between the FSS ground and the absorbing layer is investigated by an efficient equivalent transmission line approach. Criteria for enlarging the low-RCS band with respect to the free space design are also provided. An antenna array prototype backed by the thin multilayer structure is finally manufactured and tested.

We report optimized design of multilayered electromagnetic shield using real coded genetic algorithm. It is observed that the shielding effectiveness in multilayer design is higher than single layered counterpart of equal thickness. An effort has been made to develop alternative approach to achieve specific objective of identifying the design characteristics of each layer in the multilayered shielding configuration. The proposed approach incorporates interrelated factors, such as, absorption and reflection in the design optimization as per specific shielding requirements. The design problem has been solved using shielding effectiveness theory based on transmission line (TL) modeling and real-coded genetic algorithm (GA) with simulated binary crossover (SBX) and parameter-based mutation. The advantage of real-coded GA lies in efficient solution for electromagnetic interference (EMI) shielding design due to its strength in solving constraint optimization problems of continuous variables with many parameters without any gradient information. Additionally, the role of material parameters, such as permittivity and permeability on reflection characteristics and shielding effectiveness has also been investigated and optimized using the proposed models and real-coded GA. Theoretical optimization of electromagnetic parameters has been carried out for SE ~40 dB for many industrial/commercial applications and SE ~80 dB for military applications.

This work presents the results of the synthesis of a light-weight inexpensive reconfigurable planar array antenna. The antenna structure is based on four circular patches. The sources points and some discontinuities on the patches can be electronically reconfigured by means of radio-frequency (RF) switches in order to modify the radiation pattern. In particular, the main lobe could be steered towards a desired direction to obtain an optimal management of wireless resources. An experimental prototype has been realized and tested. Numerical and experimental results are reported and compared to assess the reconfigurable capabilities of the proposed antenna prototype.

In this paper, it is demonstrated how anisotropic and inhomogeneous magnetic metamaterials may be used for molding the flow of the magnetic field, considering magnetic field shielding as the main application of practical interest. It is shown that using anisotropic materials, magnetic field shielding may be improved, and this anisotropy can be realized by metamaterials. Introducing additional inhomogeneity in the metamaterial can increase the shielding performance even more. The required parameters for inhomogeneity may be obtained by representing the shielding problem in matrix form, using a quasi-static magnetic field approximation. Finally, some comments on the practical implementation of the metamaterial and comparisons with the standard shielding techniques are given.

The influence of random fluctuations in the layer thicknesses in high contrast, one-dimensional Photonic Crystals (PCs) on the transmission spectra and Photonic Band Gaps (PBGs) is investigated. The change in the PBGs depends on the magnitude of the fluctuations and increases with an increase in the order of the PBG. Introducing thickness non-uniformity into the PC of up to 0.004 times the value of lattice constant for different types of fluctuation distributions has a negligible effect on either the position or the shape of the 1st and nearest PBGs. The approach suggested here allows the determination of the tolerances required in the geometrical parameters of PCs during fabrication. It also allows the optimisation of PC structures using high order PBGs.

This paper presents a comparative study of neural network (NN) training. The trained NNs are used as adaptive beamformers of antenna arrays. The training is performed either by a recently developed method called Mutated Boolean PSO (MBPSO) or by a well known beamforming method called Minimum Variance Distortionless Response (MVDR). The training procedure starts by applying the MBPSO and the MVDR to a set of random cases where a linear antenna array receives a signal of interest (SOI) and several interference signals at random directions of arrival (DOA) different from each other in the presence of additive Gaussian noise. For each case, the MBPSO and the MVDR are independently applied to estimate respective excitation weights that make the array steer the main lobe towards the DOA of the SOI and form nulls towards the DOA of the interference signals. The lowest possible value of side lobe level (SLL) is additionally required. The weights extracted by the MBPSO and the weights extracted by the MVDR are used to train respectively two different NNs. Then, the two trained NNs are independently applied to a new set of cases, where random DOA are chosen for the SOI and the interference signals. Finally, the radiation patterns extracted by the two NNs are compared to each other regarding the steering ability of the main lobe and the nulls as well as the side lobe level. The comparison exhibits the superiority of the NN trained by the MBPSO.

This paper presents a novel planar antenna with a reconfigurable radiation pattern. The proposed layout consists of N ≥ 2 monospaced planar bowtie antennas selected one by one by means of a pair of PIN diodes. Experimental results referring to the case of N=2 and N=4 are reported and discussed demonstrating the feasibility and effectiveness of the proposed design approach.

In this paper, a novel approach to design compact multi-band loop antennas is proposed. This type of antennas is composed of coplanar waveguide (CPW)-based composite right/left-handed (CRLH) quarter-wave type resonators, and developed on a vialess single layer. Both size reduction and low frequency ratios have been achieved, profiting from the employment of quarter-wave resonators and the high nonlinearity in the left-handed region of CRLH transmission line (TL) dispersion diagram. A sample prototype operating at three negative modes (1.92/2.15/2.64 GHz) with an overall size of 29 × 21.3 × 1.0 mm³ was manufactured and measured. Measured results show good agreement with EM simulation, exhibiting good impedance matching as well as stably omni-directional radiation patterns at the three operating modes.

Joint time-frequency analysis (JTFA) is applied to micro Doppler signatures generated by jet engine modulation (JEM) effect using a modified Hilbert-Huang transform (HHT). The modified HHT is developed to improve the JTFA results of measured JEM signals. Wavelet decomposition (WD) with Meyer wavelet function is considered as a supplementary process of the HHT. The modified HHT examines a signature obtained from simulation of a jet engine CAD model, and is then applied to the signatures obtained from measurement of two realistic jet engine models. The modified HHT gives more improved JTFA results of the measured JEM signals than those from the simple short-time Fourier transform - (STFT) based analysis. The modified HHT-based JTFA approach is expected to be significantly useful for enabling high-quality radar target recognition in a real environment by complementing other traditional analyses.