For the spaceborne synthetic aperture radar (SAR) system, in order to alleviate the complexity of the imaging algorithm and to improve the accuracy of the applications of SAR images, attitude steering is required to reduce the Doppler centroid to 0 Hz. In published literature, two-dimensional attitude steering, including yaw and pitch steering, is employed for elliptic orbiting SAR systems. This paper proposes a new steering approach involving only yaw steering to suppress the Doppler centroid of the mid-range to theoretically 0 Hz with a low residual Doppler centroid at the edge of the range extent. This may reduce the complexity of the attitude control system. The comparison of the performances of the current applied methods and the proposed approach is carried out with a simulation, and the effectiveness of the new approach is validated by the results.

In order to collect information for the manufacture and application of a designed dual left-handed material (LHM) structure, the influence of salt spray test on the two conductive composite coatings consisting of silver and copper is contrastively investigated. It is found that the salt spray corrosion test can influence the microstructure of the coated copper and silver layers, leading to the decrease of electrical conductivity of the coated copper and silver layers. As results, the transmission performance of the dual-LHM structure is reduced, while the bandwidth of the dual-LHM structure is broadened. Moreover, at the same conditions, the salt spray corrosion test has less influence on the transmission characteristics of the silver-plated dual-LHM structure than those of copper-plated dual-LHM structure.

A wideband diplexer for the extended C-band feed antenna system is proposed in this paper. The diplexer operates in the receiving band (Rx) 3.625-4.8 GHz and transmitting band (Tx) 5.85-7.025 GHz, which give 28% and 19% bandwidths at Rx and Tx bands, respectively. In order to cover such a broadband, a side coupling T-shaped junction and a corrugated low-pass filter scheme are adopted. The T-shaped junction and the filter are designed separately, and then combined for optimization. A prototype is fabricated and measured. Measured results show a good agreement with the calculated ones. The return loss is less than -21 dB, transmission loss less than 0.21 dB, Rx/Tx isolation better than 45 dB, and Tx/Rx isolation better than 70 dB.

This paper proposes a horn antenna with limiting plates inside to produce symmetrical pattern in E-plane and H-plane. Sidelobes of the antenna are reduced using the limiting plates, and therefore, the beam efficiency of the antenna is improved up to 90 % without changing the antenna dimensions. The antenna dimensions are adjusted to achieve the best beam efficiency. Simultaneously, the reflection coefficient is maintained lower than -15 dB. In addition, it is indicated that this antenna has wide bandwidths without reducing the efficiency and performance of the antenna. Finally, the reflection coefficient is improved to -20 dB without degradation of the antenna performance.

A compact ultra-wideband (UWB) bandpass filter with high selectivity and deep notched band attenuation is presented in this letter. The main structure of this filter is a balun-based coplanar waveguide (CPW)-microstrip-CPW transition. This structure has UWB bandpass characteristic (2.85-11 GHz) and a transmission zero at its lower transition band. To achieve a transmission zero at its upper transition band, some complementary split ring resonators (CSRR) are added in the ground of microstrip. Therefore, this filter, whose skirt factor is 89%, presents high selectivity. Then, a notched band is created by short-ended stubs for 5.5 GHz WLAN. Owing to the stepped impedance characteristic of these stubs, this filter achieves -41 dB deep notch in its S₂₁. Besides, the size of the whole filter is only 0.38λ_g*0.45λ_g. The simulated and measured results agree well with each other.

This paper considers the broadband performance of distribution broadband over power lines (BPL) networks when a new rened theoretical coupling scheme computation module (CS2 module) is applied. The broadband performance of distribution BPL networks is investigated in terms of their channel attenuation and capacity in the 3-88MHz frequency range, which is the typical operating frequency band of BPL technology. The analysis and relevant numerical results outline the important attenuation and capacity improvement of distribution BPL networks when CS2 module is applied.

Positive semi-definite expressions for the time-domain macroscopic energy density in passive, spatially nondispersive, dipolar continua are derived from the underlying microscopic Maxwellian equations satisfied by classical models of discrete bound dipolar molecules or inclusions of the material or metamaterial continua. The microscopic derivation reveals two distinct positive semi-definite macroscopic energy expressions, one that applies to diamagnetic continua (induced magnetic dipole moments) and another that applies to paramagnetic continua (alignment of permanent magnetic dipole moments), which includes ferro(i)magnetic and antiferromagnetic materials. The diamagnetic dipoles are ``unconditionally passive'' in that their Amperian (circulating electric current) magnetic dipole moments are zero in the absence of applied fields. The analysis of paramagnetic continua, whose magnetization is caused by the alignment of randomly oriented permanent Amperian magnetic dipole moments that dominate any induced diamagnetic magnetization, is greatly simplified by first proving that the microscopic power equations for rotating permanent Amperian magnetic dipoles (which are shown to not satisfy unconditional passivity) reduce effectively to the same power equations obeyed by rotating unconditionally passive magnetic charge magnetic dipoles. The difference between the macroscopic paramagnetic and diamagnetic energy expressions is equal to a ``hidden energy'' that parallels the hidden momentum often attributed to Amperian magnetic dipoles. The microscopic derivation reveals that this hidden energy is drawn from the reservoir of inductive energy in the permanent microscopic Amperian magnetic dipole moments. The macroscopic, positive semi-definite, time-domain energy expressions are applied to lossless bianisotropic media to determine the inequalities obeyed by the frequency-domain bianisotropic constitutive parameters. Subtleties associated with the causality as well as the group and energy-transport velocities for diamagnetic media are discussed in view of the diamagnetic inequalities.

The phase and group refractive indexes of microwaves in the ionosphere region of the earth atmosphere are very important for both the researching theoretical problems and practical problems in wireless information transmission (WIT) and wireless power transmission (WPT). So far, there have been many attempts devoted to discuss and to determine the refractive indexes concerning their velocities in ionized region, unfortunately due tothe complicated features of the ionosphere region leading to research task facing with many challenges. Up to recent, there is still a lack of systematic numerical data of complex refractive index by altitude depending on high frequencies of the electromagnetic waves in the ionosphere region. This paper outlines and discusses some theoretical aspects of the complex refractive index in atmosphere's ionized region. Based on complex relative permittivity and conductivities by altitude determined numerically, the numerical estimated data of complex refractive indexes by the altitude from 100 km up to 1000 km at the different frequencies arealso shown and discussed.

In this paper, a novel resistance network node potential measurement technique based on 16-channel cycle method is presented, and a grounding grids corrosion diagnosis measurement system with 16 channels is built from this method. Through this measurement system, 1,680 valid potential data and 1,560 effective branch voltage data can be collected in one measurement by only 16 accessible node downleads on the grounding grid. The stability error of the excitation current source is less than 0.15%, and the error of the applicable acquisition data is about 1% according to system data tests. Built on the measurements, an underdetermined sensitivity equation for solving the increasing multiple of branch resistance is put in place to determine the corrosion status of grounding grids. The experimental results show that the plenty of data is necessary when solving the underdetermined equation and also show that the system is under a high stability, high accuracy, and can comply with the requirements of corrosion diagnosis for grounding grids.

Toward an engineering optimization for photonic band-gap structures in waveguide filter, this paper presents an effective optimization method using Kriging surrogate model combing with semi-analytical spectral element method to maximize photonic band-gaps. Photonic crystals are assumed to be finite periodic structures composed of two dielectric materials with different permittivities. Kriging surrogate model is used to build an approximate function relationship between the photonic band-gaps and the design parameters of photonic crystals, replacing the expensive reanalysis for electromagnetic simulations of 3D periodic structure. The semi-analytical spectral element method is used to calculate the photonic band-gaps at different sampling points. Numerical results demonstrate that the proposed optimization method can effectively obtain maximum photonic band-gaps.

This paper presents a hybrid method combining a vector fitting (VF) and a global optimization for diagnosing coupled resonator bandpass filters. The method can extract coupling matrix from the measured or the electromagnetically simulated admittance parameters (Y-parameters) of a narrow band coupled resonator bandpass filter with losses. The optimization method is used to remove the phase shift effects of the measured or the EM simulated Y-parameters caused by the loaded transmission lines at the input/output ports of a filter. VF is applied to determine the complex poles and residues of the Y-parameters without phase shift. The coupling matrix can be extracted (also called the filter diagnosis) by these complex poles and residues. The method can be used to computer-aided tuning (CAT) of a filter in the stage of this filter design and/or product process to accelerate its physical design. Three application examples illustrate the validity of the proposed method.

In this paper, a novel compact second-order quad-band bandpass filter (BPF) is applied based on a novel quintuple-mode stub-loaded trigonal ring resonator. Resonant characteristics are extracted by even- and odd-mode method. Designing procedure of resonant frequencies has also been presented. The last two resonant modes are utilized to cover a wide bandwidth for 5G WiFi application. The rest of other three resonant modes are used to form three passbands for GPS, WLAN and WiMAX applications. According to pseudo-interdigital structure four transmission zeros are generated among passbands to improve the band to band rejection and enhance the frequency selectivity. The measurement results agree well with the EM simulation ones.

In this paper, a printed split ring resonator (SRR) loaded log-periodic Koch dipole antenna (SLPKDA) is proposed. Koch-shaped dipoles when being loaded with split ring resonator (SRR) yielded a compact antenna, still preserving the radiation properties of log-periodic dipole antenna (LPDA). Measurement results show that the proposed antenna has a wide bandwidth, good impedance match and gain of 4 dBi over the band of frequencies from 0.9 GHz to 2.5 GHz. Both vertical and horizontal dimension reductions are achieved by loading Koch dipoles with SRR.

To perform the ground simulation experiments of the complex space operations, this work proposes a new active magnetic suspension compensator. The large-gap magnetic suspension compensator (LGMSC) is a conceptual design for a ground-based experiment which could be used to investigate the technology issues associated with accurate suspended element control at large gaps. This compensator can be used as the out-of-plane electromagnetic actuator for the 3-DOF fine stage in certain high precision positioning applications. Based on the equivalent current method, we explain the basics of the magnetic suspension compensator and analyze its advantages. A gravity compensator has been realized in a test setup that shows the feasibility of the chosen modeling technique and of magnetic gravity compensation.

The mathematical model elaborated in this paper is based on the concept of intrinsic modes in order to analyze and synthesize optical wave propagation along a non-uniform optical structure which is used in integrated optics communication as tapered optical coupler. The new mathematical model is simply developed by introducing modifications to the intrinsic integral, and its numerical evaluation illustrate the electromagnetic field distribution inside a taper thin film and also outside the waveguide constituted by the substrate and the cladding of lower refractive index. The proposed method permits efficiently tracking the behaviour of the optical waves both inside and outside of the optical waveguide, and quantifying the radiation and optical coupling occurring from the taper thin film of higher refractive index to adjacent mediums until a total energy transfer; this happens at thicknesses lower than waveguide cutoff thickness of each mode. The new model can be applied to all types of tapered optical coupler, having a high or low contrast of the refractive indexes, and different wedge angles formed by the different mediums of the waveguide.

In microwave imaging, accuracy of breast cancer detection depends on complex permittivity profile reconstruction in breast. Inverse scattering problem is solved to reconstruct complex permittivity profile of breast. In this paper, computation time to solve inverse scattering problem is reduced by exploiting symmetry present in breast models using group theory. Forward problem is solved using method of moments. Levenberg-Marquardt algorithm is used to solve inverse scattering problem with and without group theory. Results show that computation time is reduced considerably by exploiting symmetry present in breast models using group theory. At higher SNR, error in complex permittivity reconstruction with group theory is approximately same as error without group theory.

Axial-null illumination (ANI) is proposed to simplify the calibration of microwave imaging systems. The illumination also enhances the spatial resolution. ANI can be achieved with various array configurations, but a minimum of two transmitting antennas are required, which is a well-known form of differential illumination. Here, ANI is achieved with four transmitting antennas, and its implementation is investigated in a planar scanning scenario. The receiving antenna resides at the radiation null of the ANI array. Back-scattered reception requires an antenna at the center of the ANI array whereas forward-scattered reception requires an antenna aligned with the ANI axis, but on the opposite side of the imaged volume. The most important advantage of the proposed imaging setup is that it eliminates the need for background (or baseline) measurements, thus simplifying the system calibration. Also, it is proven that at least two-fold improvement in the spatial resolution can be achieved in near-field imaging scenarios compared to the conventional single-source illumination.

A dual-band two order filtering antenna is designed to cover both the GSM900 and GSM1900 bands. The resonator of the two order filter containsa half wavelength open-loop resonator and a T-shaped open stub. The antenna is composed of two parts. One is a printed monopole which covers lower frequency band, and the other is a strip with slot protruded from the ground plane, which covers higher frequency band. By substituting the antenna for the last resonator of the filter, the filtering antenna owns not only a good radiation function but also a good character of filter at the two working frequency bands.

The problem of electromagnetic waves radiation by a vibrators system with variable distributed surface impedance along their axes located in free space is solved by the generalized method of induced electromotive forces (EMF). The distinctive peculiarity of this method is the use of the functional distributions, obtained as a result of the analytical solution of the integral equation for the current by the asymptotic averaging method before, as the basic approximations for the currents along the impedance vibrators. The multi-parameter characteristics of three-element and multi-element antennas with variable impedance vibrators are calculated.

This paper studies the difference between retro-directive beamforming technique and retro-reflective beamforming technique in the context of wireless power transmission applications. In all of our studies, a wireless power receiver broadcasts continuous-wave pilot signal; the wireless power transmitter receives and analyzes the pilot signal; finally, the wireless power transmitter transmits continuous-wave power with phase profile conjugate to that of the received pilot signal. Our study demonstrates that a linear equi-spaced array configuration employed by the wireless power transmitter behaves as a retro-directive beamformer when the wireless power receiver resides in the far-zone of the wireless power transmitter, whereas it behaves as a retro-reflective beamformer when the wireless power receiver is not in the far-zone. This paper further investigates two types of array configurations other than linear equi-spaced array when the wireless power transmitter behaves as a retro-reflective beamformer. One is a V-shaped array, which is obtained by deforming the linear equi-spaced array to a ``V'' shape. The other is termed ``perturbed array:'' on the basis of linear equi-spaced array, all the elements' locations are perturbed randomly. It is particularly interesting to compare the equi-spaced array and perturbed array. When the wireless power receiver resides 5 or 6 wavelengths away, a 6-element equi-spaced array and a 6-element perturbed array produce the same power level at the near-zone focal point, but the maximum far-zone gain associated with the perturbed array is 1 dB lower than the equi-spaced array. All the conclusions drawn in this paper are supported by numerical results as well as experimental results.