The concept of virtual experiments is based on the idea of solving the inverse scattering problem by processing a suitable recombination of the available data, instead of those arising from the measurements. By properly designing such experiments (and without additional measurements), it is possible to enforce some peculiar field's or contrast source's properties, which can be helpful to perform the inversion in a more simple and reliable way. In this paper, we show that the factorization method can be used as a tool to design the virtual experiments. In doing so, we also provide, for the first time, an insight into its physical meaning. As an example, we exploit the virtual experiments designed via FM as the backbone of a linearized inversion approach for quantitative imaging of non-weak targets.

The paper introduces a new method for eliminating multiple-time-around detections in coherent pulsed radar systems with single constant pulse repetition frequency. The method includes the phase modulation of transmit pulses and corresponding phase demodulation at reception, which is matched to signals from the unambiguous range interval, and subsequent coherent integration followed by successive CFAR processing in range and Doppler domains. The performance of the proposed method is studied by means of statistical simulations. It is shown that the elimination performance can be essentially improved by optimizing the transmit phase modulation code. The optimization problem is formulated in terms of least-square fitting the power spectra of multiple-time-around target signals to a uniform power spectrum. Several optimum biphase codes are designed and used in the performance analysis. The analysis shows that the method can provide very high probability of elimination without noticeable degradation in the detection performance for targets from the unambiguous range interval.

This study is focused on how to obtain the effective or equivalent properties of inhomogeneous materials, which, contrary to the usual metamaterials, are assumed to possess only a sandwichlike form of heterogeneity. More specifically, the aim is to see how the method of inversion, and associated type and amount of data, condition the outcome of the inversion, notably as concerns the possibility or not of exotic features such as simultaneous negative permittivity and permeability in certain frequency intervals. Two inversion schemes are considered and compared: the Nicolson-Ross-Weir (NRW) scheme and an optimization scheme. The adopted form of the optimization scheme provides only numerical retrievals, but it applies to any number of far-field data couples, which fact makes it a useful tool for determining whether the retrieved properties of an inhomogeneous material really are independent of the angle of incidence as is required for effective properties. It is shown, via the optimization scheme, that the apparently infinite number of solutions predicted by the NRW scheme is reduced to a single solution-closest to the predictions of a mixture model-when the constraint of independence with respect to angle of incidence is invoked. Moreover, this solution exhibits none of the exotic features of the properties of the usual metamaterials except temporal dispersion and loss even when the component materials of the inhomogeneous layer are neither dispersive nor lossy.

Brain stroke incidences have arisen at an alarming rate over the past few decades. These strokes are not only life threatening, but also bring with them a very poor prognosis. There is a need to investigate the onset of stroke symptoms in a matter of few hours by the doctor. To address this, Electromagnetic Impedance Tomography (EMIT) employing microwave imaging technique is an emerging, cost-effective and portable brain stroke diagnostic modality. It has the potential for rapid stroke detection, classification and continuous brain monitoring. EMIT can supplement current brain imaging and diagnostic tools (CT, MRI or PET) due to its safe, non-ionizing and non-invasive features. It relies on the significant contrast between dielectric properties of the normal and abnormal brain tissues. In this paper, a comparison of microwave signals scattering from an anatomically realistic human head model in the presence and absence of brain stroke is presented. The head model also incorporates the heterogenic and frequency-dispersive behavior of brain tissues for the simulation setup. To study the interaction between microwave signals and the multilayer structure of head, a forward model has been formulated and evaluated using Finite Element Method (FEM). Specific Absorption Rate (SAR) analysis is also performed to comply with safety limits of the transmitted signals for minimum ionizing effects to brain tissues, while ensuring maximum signal penetration into the head.

As important fundamental equipment, high voltage switchgears are widely used in electric power systems and directly relative to the power reliability and quality. Partial discharge (PD) online monitoring is one of the most effective methods used for insulation testing and diagnosis in high voltage switchgears and power systems. This paper proposes a unique ultra-wide-band (UWB) antenna with high performance for PD ultra-high-frequency (UHF) detection in high voltage switchgears. Actual PD experiments were carried out, and the designed antenna was used for PD measurements. The measured results demonstrate that the proposed antenna has wide work frequency band, good omnidirectional radiation patterns and appreciable gain, which indicate that the proposed antenna is suitable for UHF online monitoring of PDs in high voltage switchgears.

A new compact interdigital capacitor loaded open slot antenna and its lumped model are presented in this letter. Equivalent model analysis shows that the introduction of the interdigital structure increases the capacitive element of the slot and thus reduces the operating frequency of the slot antenna. And the antenna operating frequency as well as its size can be easily reduced by simply increasing the capacitance of the interdigital capacitor and the characteristic impedance of the slot. Experimental results of the exemplary antenna agree well with those of the full-wave simulation, proving that the proposed open slot antenna structure is viable in antenna design.

Two numerical methods are proposed to solve the electric impedance tomography (EIT) problem in a domain with arbitrary boundary shape. The rst is the new fast Fourier transform subspace-based optimization method (NFFT-SOM). Instead of implementing optimization within the subspace spanned by smaller singular vectors in subspace-based optimization method (SOM), a space spanned by complete Fourier bases is used in the proposed NFFT-SOM. We discuss the advantages and disadvantages of the proposed method through numerical simulations and comparisons with traditional SOM. The second is the low frequency subspace optimized method (LF-SOM), in which we replace the deterministic current and noise subspace in SOM with low frequency current and space spanned by discrete Fourier bases, respectively. We give a detailed analysis of strengths and weaknesses of LF-SOM through comparisons with mentioned SOM and NFFT-SOM in solving EIT problem in a domain with arbitrary boundary shape.

In this paper, a novel quasi-periodic structure for rectangular waveguide technology is proposed. The constituent unit cells of the structure feature a resonant behavior, providing high attenuation levels in the stopband with a compact (small period) size. By applying a smooth taper-like variation to the height of the periodic structure, very good matching is achieved in the passband while the bandwidth of the stopband is strongly increased. Moreover, by smoothly tapering the width of the structure, a band-pass frequency behavior is obtained. In order to demonstrate the capabilities of the novel quasi-periodic structure proposed, a band-pass structure with good matching, wide rejected band, and high-power handling capability has been designed, fabricated, and measured obtaining very good results.

In this study, a Six-port Reflectometer (SPR) with dielectric probe sensor is used to predict relative dielectric, ε_rof normal and tumorous breast tissue in frequency range from 2.34\,GHz to 3.0 GHz. Other than that, a superstrate with an exterior copper layer is overlaid on the surface of a primitive Five-port Ring Circuit (FPRC), which is also a denominated, enhanced superstrate FPRC. It is the main component of the SPR and is presented in this paper as well. The enhanced superstrate FPRC is capable of improving its operating bandwidth by 26{\%} and shifting the operating centre frequency to a lower value without increasing circuit physical size. The detailed design and characteristics of the FPRC are described here. In addition, the enhanced superstrate FPRC is integrated into the SPR for one-port reflection coefficient measurement. The measurement using the SPR is benchmarked with Agilent's E5071C Vector Network Analyzer (VNA) for one-port reflection coefficient. Maximum absolute mean error of the linear magnitude and phase measurements are recorded to be 0.03 and 5.50°, respectively. In addition, maximum absolute error of the predicted dielectric and loss factor are 1.77 and 0.61, respectively.

A clubs-shaped wideband antenna with reconfigurable radiation pattern is proposed. This antenna is composed of two tapered slots of mirror symmetry, embedded with two PIN diodes and fed by a 50 Ω coplanar waveguide (CPW). By controlling states of PIN diodes, two tapered slots can be shut down or opened. Consequently, the proposed antenna works in three radiation modes: one monopole pattern with a simulation frequency band (3.93-5.55 GHz) and two end-fire patterns with an identical band (3.29-6.13 GHz). The antenna is fabricated and tested. Measured results show good agreement with the simulation, which denotes that it is suitable for wideband wireless communication systems.

Low-Loss resonators with high Q factor have special importance in modern microwave telecommunications systems. In this paper, a modern dual-band CSRR with high Q factor is first examined using SIW technology on a surface waveguide. It should be noted that the proposed structure paves suitable way for emitting and propagating wave in two passing bands (approx. 4.7 and 5.3 GHz) below cutoff frequency waveguide. High Q factor and its high small sized percentage is the salient specification of this structure as compared to other similar planar resonators proposed in various references. At the end of this paper, three applications of this resonator are studied in designing a small multi-band filter with high Q factor, a small multi band diplexer with low passage bandwidth and a planar oscillator with low-phase noise. According to the scientific literature, the proposed oscillator was found to enjoy the best performance at low phase noise for planar microwave oscillators.

A new technique for mutual coupling reduction, based on the application of electric resonator, is presented in this paper. In this method, first a custom-designed unitcell is presented that provides a proper S₁₂ response for the mutual coupling reduction, and then, this unitcell is used in a two-element array of wideband dipoles. According to the results, this unitcell provides a maximum reduction of 15 dB in the frequency response of the antenna array while does not have a considerable effect on the reflection coefficient and radiation pattern of the antenna. To verify the results, the antenna is fabricated and measured, and there is a very good agreement between the simulation and measurement.

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.