This paper presents a dual-band, low profile antenna with reduced specific absorption rate (SAR) for mobile handset applications. Here, dual-band operation is obtained by combining a printed dipole antenna (initially resonating at 4.3 GHz) with EBG mushroom-like structures loaded with circular slots (CS). The final structure operates at 3.44 GHz (additional band required for LTE Advanced LTE-A) and 4.5 GHz (for Smartphone WLAN applications) with improved bandwidth and reflection coefficient (350-MHz around 3.5 GHz with -26 dB, and 330 MHz around 4.5 GHz with -30 dB). Finally, a dosimetry study of the proposed printed dual-band dipole antenna is presented and verifies an SAR reduction from 9 W/Kg to 1.41W/Kg compared to the same antenna without any loading structure, and from 3.98 W/Kg to 1.41 W/Kg compared to a standard EBG mushroom-like structure.

This article proposes a new scheme of real-coefficient fitting both Green's function and its gradient with Fast Fourier Transform (RFGG-FG-FFT) for combined field integral equation (CFIE) to compute the conducting object's electromagnetic scattering, which improves original fitting both Green's function and its gradient with Fast Fourier Transform (FGG-FG-FFT) on efficiency. Firstly, based on Moore-Penrose generalized inverse, an equivalent form of fitting matrix equation is obtained containing the property of Green's function's integral proved by addition theorem. Based on this property, with truncated Green's function new fitting technique is presented for computing fitting coefficients with real value expression, which is different from complex value expression by the original fitting technique in FGG-FG-FFT. Numerical analysis of error shows that new fitting technique has the same accuracy, but only one half of sparse matrices' storage compared to the original fitting technique in FGG-FG-FFT. Finally, the new scheme combining FGG-FG-FFT and new fitting technique is constructed. Some examples show that the new scheme is accurate and effective compared to FGG-FG-FFT and p-FFT.

In this work, the problem of mutually coupled dipole antenna array failure has been solved using bat algorithm by adjusting only the amplitude excitation of good array elements. The element failure causes the degradation of side-lobe power level to an improper level. A fitness function is formulated to obtain the difference between degraded side-lobe pattern and measured side-lobe pattern, and a flexible approach using bat algorithm is used to minimize this function. Numerical examples of single and multiple element failure correction under mutual coupling conditions are discussed to show the capability of this proposed approach.

A visibility-domain processing for optical interferometric imaging (VP-OII) method is proposed to model the visibility distribution of an image, and a phase retrieval technique is proposed to acquire additional visibility data from the powerspectrum and closure-phase data. This method requires only a few tunable parameters, and can be easily extended to include more data acquired from different instruments. By simulating the reconstruction of an LkHα 101 image, the proposed method proves a few hundreds times faster and is more resilient to noises than the conventional MIRA, and the image quality is comparable to noise that of conventional MIRA.

This paper describes a frequency-tunable phase inverter based on a slot-line resonator for the first time. The control circuit is designed and located on the defected ground. None of dc block capacitors are needed in the microstrip line. A wide tuning frequency range is accomplished by the use of the slot-line resonator with two varactors and a single control voltage. A 180-degree phase inverter is achieved by means of reversing electric field with two metallic via holes connecting the microstrip and ground plane. The graphic method is used to estimate the operation frequency. For verification, a frequency-tunable phase inverter is fabricated and measured. The measured results show a wide tuning frequency range from 1.1 GHz to 1.75 GHz with better than 20-dB return loss. The measured results are in good agreement with the simulated ones.

The properties of higher order radial modes of electromagnetic azimuthal surfacetype waves (ASW) which propagate in partially plasma-filled cylindrical waveguides without external magnetic field are analyzed using analytical and numerical techniques. For a waveguide with plasma surrounded by dielectric material and encased in metal, the eigenfrequencies for higher order radial modes are obtained. It is found that the ASW higher radial modes propagate with shorter vacuum wavelength than the zero-th order radial modes and that the more favourable conditions for higher order radial mode propagation are for ASW's with larger azimuthal wavenumber in waveguides with wider dielectric layer and larger dielectric constant. A further salient feature of ASW higher radial modes is that a change in plasma waveguide parameters causes a drastic change in ASW eigenfrequency in contrast to the zero-th order modes which have a smoother frequency variation with effective wavenumber.

The improvement in the power density in the double stator configurations is feasible with increase in the electrical loading of the electrical machines. This type of newer configuration is finding significant applications in improvising energy generation, more commonly for renewable energy generation. Various double stator configurations with non-arc permanent magnet machines for power density are modelled and analyzed in this paper. Finite Element Method (FEM) is used to simulate for the generation capability including the electromagnetics parameters such as flux linkage and open circuit voltage. A new slotted rotor structure is evolved based on the magnetic flux flow control inside the machine. The proposed structure is then fabricated in the laboratory and tested for operating characteristics with load circuit. The proposed machine produces a maximum power of 600 W at speed of 2000 rpm with 75% of maximum efficiency with the micro-hydro generation unit.

In recently developed wireless communication systems, circular polarization (CP) antennas are used for communication links to reduce the natural loss effect in receivers. Therefore, in this paper, a dual-band microstrip slot antenna based on a parallel split ring resonator with circular and linear polarization which can be used for wireless and WiMAX applications is presented. The final antenna to design is based on inspired split ring resonators (SRR) to achieve circular polarization and compact size and with special parallel form of the SRR and straight feed line. We have achieved higher bandwidth in the requested frequency range with dual-band characteristics. The final antenna has a bidirectional pattern with circular polarization at the range of 2.9-3.65 GHz and bandwidths of 2-3.6 and 3.8-4.8 GHz with VSWR<2 for WLAN, Bluetooth and radar applications for IEEE WLAN protocol with gain of 5-6 dBi, respectively. The size of the prototype patch antenna is 40×40 mm². It is designed and fabricated on an FR-4 low cost substrate with ε_r=4.4 and a thickness of 1.6 mm. It is simulated using HFSS full wave software. In addition, the experimental results are presented and compared with simulation for VSWR, radiation patterns and axial ratio. The periodic analysis has been used for extracting the metamaterial parameters.

Imaging and scaling of precession targets are very important in spatial target surveillance. The bistatic wideband radar echo model of the spatial precession cone-shaped target is induced, and bistatic ISAR imaging method based on time-frequency analysis is described. Combined with the monostatic and bistatic scattering characteristics of cone-shaped targets, the cross scaling method is presented through range instantaneous Doppler (RID) image matching using T/R-R bistatic radar observations, and the correct scaled monostatic and bistatic two-dimensional images can be obtained at the same time, which can reflect the actual size of the target. The algorithm is validated by dynamic simulation with electromagnetic computation data and provides a feasible way for the stable recognition of spatial targets.

An effective fast equivalent cable bundle modeling method is proposed in this paper to study electromagnetic pulse response of complex cable bundle. Compared with traditional equivalent cable bundle method (ECBM), the complete cable bundle is equivalent to only one cable by modification of cable grouping method, which leads to reduction in number of cables and computation progress. The proposed method can perform well not only in pure resistance case, but also in frequency dependent load case by weighted average method (WAM). The computation time and memory acquirement for complete cable bundle model terminated in arbitrary loads have been further reduced by fast equivalent method compared to ECBM, and calculation precision is maintained to meet fast application need. Numerical simulation of coupled currents in observed cable located at a certain distance away from cable bundle by CST software is given to verify accuracy of the method under illumination of high altitude electromagnetic pulse (HEMP).

In this paper, a portable frequency domain electromagnetic system CEM-2 is presented for shallow metal targets detection. This paper discusses the detection principle of frequency domain electromagnetic system, introduces hardware implementation, presents test results of each module, and gives the system's imaging results in field tests. Sinusoidal pulse width modulation technique is employed in this system to produce single-frequency or multi-frequencies synthetic electromagnetic signals with signal to noise ratio of about 85 dB. After integration, the CEM-2 system's in-phase noise level is about 90 ppm while the quadrature response is about 100 ppm. The experiment results of CEM-2 agree well with the simulation ones both from signatures and amplitudes. The experiment for detecting targets of different sizes and materials conducted in field indicates that CEM-2 system can be used to distinguish metallic and ferrous objects.

This paper presents a broadband and compact planar quasi-Yagi antenna for multi-band 3G/4G applications.The proposed quasi-Yagi antenna consists of a modified bow-tie driver to increase the bandwidth, a passive reflector and two passive directors to enhance the directivity at the lower and higher ends of the operating band, respectively. A microstrip-to-slotline transition feed is used to achieve a good impedance matching. It is confirmed by experiment that general approaches for increasing the bandwidth of bow-tie antennas are also feasible for quasi-Yagi antennas with bow-tie drivers. Furthermore, with the modified bow-tie structure, the directivity of the antenna at higher frequencies of the operating band is enhanced, because the bow-tie shape can form planar horn structures and has strong current distributions at high frequencies. The proposed antenna is fabricated using an FR4 substrate with a dielectric constant of 4.2, and the overall dimension of the antenna is 1.24λ_gc×0.94λ_gc. Measurements show that the 10 dB return loss bandwidth is 80.4%, operating from 1.45 to 3.4 GHz. Measured gains are greater than 4 dBi within the entire bandwidth, and the front-to-back ratios are greater than 10 dB. Having a multi-band coverage within the 3G/4G spectra,this antenna is expected to be used for 3G/4G mobile wireless communications.

When compressive sensing was employed to solve electromagnetic scattering problems over wide incident angles, the selection of sparse transform strongly affects the efficiency of the CS algorithm. Different sparse transforms will require different numbers of measurement. Thus, constructing a highly efficient sparse transform is the most important work for the CS-based electromagnetic scattering computing. Based on the linear relation between current and excitation vectors over wide incident angles, we adopt the excitation matrix as sparse transform directly to obtain a suitable sparse representation of the induced currents. The feasibility and basic principle of the algorithm are elaborated in detail, and the performance of the proposed sparse transform is validated in numerical results.

A highly integrated X-band receiver module is designed based on a 10-layered low temperature co-fired ceramic (LTCC) substrate. A compact X-band bandpass filter (BPF), an intermediate frequency (IF) band hybrid and an IF band BPF are proposed for the receiver module. The measured gain parameter of the proposed receiver is higher than 51 dB, and noise figure (NF) and image rejection are better than 2.5 dB and 37 dB, respectively. The overall size of the receiver module is only 54 mm × 15 mm × 1 mm. Comparisons and discussions are also provided.

Two small size multiple-input-multiple-out (MIMO) antennas with high isolation for ultrawideband (UWB) applications are presented. A two-element MIMO antenna, which is mounted on an FR4 substrate with a compact size of 24 mm × 33 mm, consists of two symmetric circular monopole elements and a modified ground. The protruded ground provides a way to improve isolation and impedance matching. Such a wide band from 2.75 to 11 GHz is achieved by using modified ground technology, and high isolation more than 20 dB is also accomplished. Meanwhile, moderate gain and omnidirectional radiation patterns can be obtained. Based on the circular monopole with modified ground, a four-element antenna array is also constructed and studied. The size of the four-element antenna with orthogonal arrangement is 44 mm × 44 mm. Measured results show that the antenna also exhibits good impedance matching as well as low envelope correlation coefficient over the entire UWB spectrum.

This paper presents a heart-shaped planar monopole antenna for ultra-wideband (UWB) applications. To increase the impedance bandwidth of the antenna and achieve UWB coverage, we use a heart-shaped radiating patch fed by a microstrip line and an elliptical curved ground plane. Based on this structure, by etching an annular slot loaded with a capacitor in the heart-shaped radiating patch, a planar band-notched UWB antenna can also be obtained. Specifically, to demonstrate the potential application of the proposed structure, a UWB antenna design with a reconfigurable notched band is presented by using a varactor to replace the capacitor. Commercial software ANSYS HFSS is used to analyze and design this antenna. Measured results of the fabricated antenna show good agreement with simulated ones.

This paper proposes a compact and miniaturized branch-line coupler using a crossing bond wire structured slow-wave branch line (CBWSWB). The proposed coupler achieves a size reduction of 82% compared with a conventional implementation. Measured S₁₁, S₂₁, S₃₁ and S₄₁ of the proposed coupler are better than -24, -3.7, -3.7 and -28 dB at 3 GHz, respectively. Furthermore, the phase difference between through and coupling ports of the coupler is within 1°.

In order to improve the angle measurement precision with a low computational complexity, a 2-D direction of arrival (DOA) estimation algorithm UCA-TF-MI-ESPRIT is proposed in this paper. This algorithm is based on the mode space algorithm and the time-frequency (TF) multiple invariance rotational invariance technique (MI-ESPRIT). Firstly, a uniform circular array (UCA) is equivalent to a virtual uniform linear array (ULA) by utilizing mode-space algorithm. Then, the smoothed pseudo Wigner-Ville distribution (SPWVD) of the ULA output is calculated. The spatial time-frequency matrix can be obtained through the average of multiple time-frequency points in the time-frequency plane, and the signal subspace can also be obtained through using eigen decomposition. Then a simple and effective subarray dividing approach is proposed, and the multiple rotational invariant equation of the array is obtained by using the Bessel function. Finally, the closed-form solution is obtained using multi-least-squares (MLS) criterion so that the 2-D DOA estimation of LFM signals in UCA is completed. The simulation results verify the effectiveness of the algorithm proposed by this paper.

Diffraction tomography (DT) from limited projection data has been an active research topic for over three decades. The interest has been steadily fueled due to its application in multiple disciplines including medical imaging, structural health monitoring and non-destructive evaluation to name a few. This paper explores the applicability of compressed sensing to recover complex-valued objective functions (e.g., complex permittivity in microwave tomography). Generally, compressed sensing based tomographic reconstruction has been studied under full angular access. In this paper, the effect of lowering the angular access in addition to highly limited number of projection data is explored. The effectiveness of the reconstruction methods is tested with severely limited dataset which would render reconstruction impossible by traditional iterative approximation methods. Furthermore, results show that complex-valued phantoms can be reconstructed from as few as 15 projections from 120˚ coverage, a significant finding. In this study, the Total Variation (TV) has been used as the l₁ norm within the compressed sensing framework. The robustness of the algorithm in presence of noise is discussed. Use of multiple sparse domains has also been explored briefly. The results show the effectiveness of TV as a regularization parameter even for complex-valued images under the compressed sensing regime. This is a pertinent observation as TV is a simple norm to implement. For a large class of images, especially in medical imaging, this implies the availability of a steady l₁ norm for easy implementation of compressed sensing reconstruction for complex-valued images.

A LEO-ground infrared laser occultation (LGIO) technique is proposed to retrieve the greenhouse gas (GHG) profiles around a specific location, including the analysis of key factors and practical issues that may affects its efficacy. A harmony search with ensemble consideration (HS-EC) algorithm is applied to retrieve the volume mixing ratio (VMR) profiles of H₂O and three major GHGs, CO₂, CH₄ and N₂O. The vertical resolution of retrieved GHG profiles is 1 km from ground level up to 20 km at height. The errors in VMR of H₂O, CH₄, N₂O and CO₂ are below 10, 5, 5 and 3%, respectively, up to 45 km above ground.