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.

Two approaches to reconstruct the S-matrix of N-port waveguide reciprocal devices from 2-port S-matrix measurements are proposed and discussed. The main advantage of the proposed approaches is that measurements are done always at the same two ports, without moving the device. The remaining N-2 ports are loaded with different loads, either matched or short. The first approach, based on a manipulation of the 2-port S-matrices, requires N-2 matched and two other loads, while the second approach, based on the evaluation of an equivalent circuit, requires N-2 short and two other loads. The measurement technique is based on the standard loads (short, shift and matched) in the waveguide calibration kit of the 2-port VNA.

Non-circular properties of non-circular signals can be used to improve the performance of the direction-of-arrival (DOA) estimation. However, most ready-made algorithms are not applicable to the general case in which both non-circular and circular signals exist. In this paper, we present a novel DOA estimation algorithm for mixed signals, namely MS-MUSIC (Mixed Signals - Multiple Signals Classification), which can deal with the two kinds of signals simultaneously. And on this basis, we derive the Cramer-Rao Lower Bound (CRLB) of the azimuth and elevation estimation. The effectiveness of the algorithm is confirmed by the simulation results. Meanwhile, it acquires higher accuracy than the traditional algorithms.

In this paper, we present results of characterization of a bifacial silicon solar cell, under multispectral steady state illumination, using finite elementmethod (FEM). The illumination level (n) and back surface recombination velocities (Sb) effects on solar cell electrical parameters have been highlighted. After solving the continuity equation that describes the solar cell operation, the excess minority carrier's density and current-voltage characteristics are determined for various values of illumination level and recombination velocities on the junction and the back surface of the solar cell. The results obtained are in agreement with those given by analytical methods and prove that the photovoltaic cells can be analyzed only by numerical methods, such asthe FEM, characterized by their robustness and flexibility in their applicationsin a context where those methods take more and more importancein the development of Computer Aided Design (CAD) tools.

In this paper, a frequency reconfigurable Antipodal Vivaldi Antenna (AVA), capable of covering a Band of Interest (BoI) spanning from 3 to 10.6 GHz with four different bandwidth resolutions, is presented. By incorporating four rectilinear resonators and two Split-Ring-Resonators (SRRs) into the AVA, the whole BoI can be covered by one (UWB mode), three (3-sub mode), seven (7-sub mode), or sixteen (16-sub mode) sub-bands. In the UWB-mode, all the six resonators are deactivated by disrupting their structures, so the antenna operates as a classical AVA. In the 3-sub mode, only one rectilinear resonator is activated; the low Q of these resonators allow narrowing the antenna operating band so that the BoI is covered by three sub-bands. In the 7-sub mode, two rectilinear resonators are activated at a time, which narrows the operating bandwidth furthermore, allowing to cover the BoI by seven sub-bands. In the 16-sub mode, one of the two SRRs is activated at a time to be used as a coupling-bridge to very narrow frequency bands that allows covering the BoI by sixteen different bands. To present the work, simulated and measured results are given and discussed.

One-side boundary conditions on the field inside core region are obtained for core-cladding waveguide with anisotropic cladding. The boundary conditions involve two functions acting as components of anisotropic surface impedance for cladding material. These functions are determined in relation to desired values for step-index waveguide and dielectric-lined waveguide with either perfectly or finitely conducting walls. With resulting surface impedance, the perfect analogy between core-cladding and impedance waveguide is achieved. Using this analogy, independent eigenvalue problems are obtained for membrane functions of HE and EH waves of core-cladding waveguide. From this result some conclusions about electromagnetic properties of HE and EH waves are drawn.

In this paper a CPW-fed annular slot antenna is miniaturized with enhanced impedance bandwidth using a reactive impedance surface (RIS) substrate. Such meta-surface (RIS) is realized by patterning 3×3 array of circular elements over an inexpensive FR-4 substrate which is backed by a circular metallic plane. Due to the compensation of electric and magnetic energy stored by antenna and RIS substrate respectively, the antenna resonance frequency is shifted by 53.6% compared with a simple slot antenna. By the inclusion of such reactive surface, input impedance of the antenna is reduced, and a remarkable improvement in impedance bandwidth from 11.66% to 64.26% is also noticed. Therefore, both miniaturization and bandwidth enhancement are achieved simultaneously with the present loading technique. The directivity of the RIS loaded antenna is increased further by loading a concentric metallic ring over the RIS loaded structure at a height above the RIS plane. The Ring & RIS loaded structure is fabricated for measurement purpose. A good agreement is obtained between the simulated and measured results for both RIS loaded and Ring & RIS loaded configurations. The ring loading over the RIS antenna provides improvement in directivity about 5 dB. The peak gain and bandwidth are measured as -1.03 dBi and 58.62%, respectively.

A triple-band planar electromagnetic band-gap (EBG) structure used for gain enhancement and wideband radar cross section reduction (RCSR) of antenna is presented in this paper. Three band-gaps of an EBG structure are realized by introducing two pla-nar spiral inductances on a planar EBG structure. An equivalent model of EBG is given to further understand the formation of three band-gaps. The proposed EBG is placed around antenna units and arrays to calculate the affection of the RCS and the gain. Due to the band-gaps of the EBG structure, RCS of antennas is reduced, and the gain of antennas is enhanced. Results show that the RCS is reduced as much as 20 dB from 9 GHz to 21 GHz, and both of bandwidth and gain of antennas can be slightly enhanced. Two antenna units operating at 8.6 GHz are fabricated and measured to verify the correctness of simulation. Measured and simulated results are in good agreement.

A compact circularly polarized antenna using a wide L-shaped slot and a microstrip feedline is proposed. The measured results demonstrate that the antenna has an axial ratio (AR) < 3 dB bandwidth ranging from 5-8.5 GHz and an S₁₁ < -10 dB bandwidth ranging from 4-8.6 GHz. The antenna is very simple, composed of an L-slot and a microstrip feedline placed beneath and to the edge of the L-slot. The size of the antenna is 20 x 20 mm² which is attractive for compact wireless devices that operate in C-band. The antenna has very low cost and does not require: a large size, truncated corners, reflecting surfaces, complex feeding structure, and via connections, which increase fabrication cost and design complexity.