This paper presents a novel tunable microstrip patch antenna using liquid crystal. It adopts a differentially-driven, aperture-coupled, and stacked-patch structure. Compared with the conventional design, this novel antenna achieves a larger frequency tuning range, much wider impedance bandwidth, higher radiation efficiency and gain. Besides, the novel antenna facilitates the bias design as the bias signal is naturally isolated from the RF signal. Both the conventional and novel antennas are designed to operate at 28 GHz using an RT/Duroid 5880 substrate and K15 liquid crystal. Results show that the novel antenna has a tuning range of 3.1%, an impedance bandwidth of 6.43%, a peak radiation efficiency of 70%, and a peak realized gain of 6.5 dBi, while the conventional antenna has the tuning range of 2.7%, impedance bandwidth of 3.57%, peak radiation efficiency of 45%, and peak realized peak gain of 4.5 dBi.

Standing wave between the feed and the reflectarray (RA) deteriorates the matching and antenna gain. A phase perturbation method is investigated to improve the matching of the antenna. The proposed method requires a change or deformation of the RA area facing the feed. A small circularly polarized reflectarray (CPRA) is used as an example. The reflectarray size is 6.25λ×6.25λ, which is corresponding to 25×25 elements. The feed is circularly polarized (CP) with aperture diameter 1.2×λ. The proposed method provides an acceptable compromise between achieving the matching and gain reduction. The field distribution on the symmetric line between the RA center and the feed is observed to show the behavior of the standing wave before and after implementing the proposed technique. The measured return loss becomes better than 10 dB, and a gain reduction is 0.2 dB. A measured maximum aperture efficiency of 55.4%, a 1-dB gain bandwidth of better than 33%, and the 1.5-dB axial ratio bandwidth of 33.2% are achieved.

In this paper, a novel technique for improving the torque characteristics of the Interior Permanent Magnet Synchronous Motor is proposed using rotor shape optimization. The main objective is to decrease the torque ripple while increasing average torque. The improvement process is performed for the maximum torque-angle operating point, and then studies are carried out for other currents and angles. Defining a multi-element grid on rotor surface regions in which each element could be either iron or air, the best practical rotor surface topology could be obtained to improve the overall torque characteristics of IPMSM. The best motor performance is achieved using practical rotor shapes obtained from a cluster of points in average torque versus torque ripple plane. Finally, for torque ripple cancellation, two or three alternate rotor configurations with optimized average torque and out of phase torque pulsation have been selected. This selection will guarantee improved average torque while mitigating torque pulsation by a significant margin. Using this method, a rotor topology obtained in which torque ripple is reduced by 80% with slightly improved average torque.

Several computer codes with varying accuracy from rigorous full-wave methods (highfidelity models) to less accurate Transmission Line (TL) approaches (low-fidelity model) have been proposed to solve EMC problems of interference between parasitic waves and wired communication systems. For solving engineering tasks, with a limited computational budget, we need to build surrogate models of high-fidelity (HF) computer codes. However, one of their main limitations is their expensive computational time. Rather than using only the computationally costly HF simulations, we apply another type of surrogate models, called Multifidelity (MF) metamodel which efficiently combines, within a Bayesian framework, high and low-fidelity (LF) evaluations to speed up the surrogate model building. The numerical results of combination of an expensive EMC simulator and a cheap TL code to solve a plane wave illumination problem, show that, compared to Kriging, a reliable Bayesian MF metamodel of equivalent or higher predictivity can be obtained within less simulation time.

In this paper, a broadband circularly polarized (CP) antenna based on slot-loaded dipole with L-shaped arms and parasitic patches is proposed and investigated. Circular polarization is initially obtained at the lower frequency by bending the dipole arms into L-shape. To extend the axial ratio (AR) bandwidth, two pairs of parasitic patches are introduced along the orthogonal sections of the L-shaped arms, so that the modified dipole can yield two additional minimum AR points at the center and higher frequency respectively. Meanwhile, to further extend impedance bandwidth and improve CP performance, circular slots are symmetrically embedded into the tapered-end of each arm design. The measured results of the antenna exhibit a 3-dB AR bandwidth of 61.3% within 10-dB return loss bandwidth of 64.0%. Besides, desirable gains across the wide operation band are also demonstrated.

The quantum radar cross section (QRCS) is a concept that gives information on the amount of returns (or scattered energy towards the detector) one can expect from a particular target when being illuminated with a small number of photons. This cross section is highly dependent on the target's geometry, as well as the illumination angle and the scattering angle from the target. The expression for the quantum radar cross section equation has been derived in the context of photon scattering. In this paper, it will be shown that an equivalent cross section expression, including the alternate form written in terms of Fourier transforms, can be derived using quantum scattering theory applied to non-relativistic, massive particles. Both single particle and multiple particle illumination are considered. Although this approach is formulated based upon massive, non-relativistic particle scattering, its equivalence to the expression based upon photon scattering provide many valuable insights of representing and interpreting these equations in the context of quantum radar. This includes an improved algorithm to simulate the QRCS response of an object illuminated with any number of photons desired.

This paper demonstrates a new class of highly selective bandstop filter based on cascading two identical lossy hybrid dual-band bandstop filters of low resonator Q factor. Each filter is synthesized based on multi-stage predistortion reflection mode technique. To demonstrate the approach, 4th order hybrid dual-band elliptic filter network which is a product of elliptic lowpass and highpass network functions has been predistorted and synthesized with low calculated Q factor. The lossy dual-band bandstop filters are fabricated and realized on microstrip planar structure. Both theoretical and experimental results clearly show good agreements with two stopband rejections up to 35 dB for one stage and 50 dB for two stages with passband loss of more than 10 dB.

This communication demonstrates the feasibility of rectifying microwave energy through one-wire with no earth return. In the proposed transmission system, a novel coaxial to Goubau line transition (referred thereafter as coaxial/G-line transition) was employed to transfer microwave power from TEM modes in a coaxial line to TM modes in a Goubau line. The captured signal at the receiving end of the Goubau line can be either directly used for communication or rectified into a DC. The proposed system can be used as an emergency source of power supply for cable cars, escalators and window cleaning gondolas in the event of accidents. According to our experimental results, a 0 dBm microwave signal can be transmitted through a single conductor of 13 cm in length with an insertion loss of less than 3 dB. When the input power was raised to 15 dBm, the electromagnetic energy at the receiving end can be rectified at 1.36 GHz into a DC with the efficiency at approximately 12.7%.

This paper describes the design of a two-pole low-pass and band-stop filters. The low-pass structure is designed at the cutoff frequency of 2 GHz for the L-band applications. This architecture uses half circle defected ground structure HCDGS instead full circle DGS resonator. Both the HCDGS shapes are etched in the ground plane and coupled via a substrate with a compensated capacitor. The rejection bandwidth of the LPF covers a large wideband spectrum. Therefore, the band suppression reaches more than 3fc. The filter is simulated and fabricated. The measured results are in good agreement with the full-wave simulated ones, showing the merits of compact size and sharp roll-off. The multi-layer technique has been used, In order to realize a transformation from low-pass behaviours to band-stop characteristics, keeping the same passband features. The new extracted band-stop topology is simulated and optimized using an RO4003 substrate with dielectric constant of 3.38 and thickness of h = 0.813 mm. The structure has a wide stopband with over 20 dB rejection from 11 to 20 GHz. Such filters can be used for L-band and military applications.

A low-profile bandwidth-enhanced zeroth-order resonant (ZOR) antenna based on composite right/left-handed transmission line (CRLH-TL) theory loaded by parasitic element is presented in this paper. The bandwidth and efficiency of the proposed ZOR antenna is improved simultaneously by introducing a parasitic element resonating within the CRLH-TL band-stop. The dispersive behavior of the ZOR antenna is analyzed by performing full-wave simulation using CST microwave studio and compared with the theoretical circuit model. The overall dimensions of the proposed antenna is 0.303λ₀×0.248λ₀×0.003λ₀. The antenna has been fabricated and tested. The experimental results exhibit widem operational bandwidth of 87.1% and excellent radiation efficiency up to 95.7%. Owing to the symmetrical configuration of the proposed design the polarization purity better than -14 dB is obtained. The measured results are in very good agreement with the simulation. The compact, uni-planar and via-less configuration of the proposed antenna with reasonable polarization purity makes it desirable to be used for modern wireless communication systems such as GSM, UMTS, WiMAX, WLAN and LTE.

The problem of axially-symmetric TM-wave diffraction from the perfectly conducting sphere-conical cavity is analysed. The cavity is formed by a semi-infinite truncated cone; one of the sectors of this cone is covered by the spherical diaphragm. The problem is formulated in terms of scalar potential for spherical coordinate system as a mixed boundary problem for Helmholtz equation. The unknown scalar potential of the diffracted field is sought as expansion in series of eigenfunctions for each region, formed by the sphere-conical cavity. Using the mode matching technique and orthogonality properties of the eigenfunctions, the solution to the problem is reduced to an infinite set of linear algebraic equations (ISLAE). The main part of asymptotic of ISLAE matrix elements determined for large indexes identifies the convolution type operator. The corresponding inverse operator is represented in an explicit form. The convolution type operator and corresponding inverse operator are applied to reduce the problem to the ISLAE of the second kind. This procedure determines the new analytical regularization method for the solution of wave diffraction problems for the sphere-conical cavity. The unknown expansion coefficients, which are determined from the ISLAE by the reduction, belong to the space of sequences that allow obtaining the solution which satisfies all the necessary conditions with the given accuracy. The particular cases, such as transition from sphereconical cavity to the open hemispherical resonator, as well as the low frequency approximation, are analysed. The numerically obtained results are applied to the analysis of TM-waves radiation through the circular hole in the cavity.

In medical microwave imaging applications, electromagnetic (EM) waves propagate through human tissues, which are inherently attenuative and dispersive. In the resulting image, these effects translate to a lack of resolution that increases with time/distance. To produce microwave images with high resolution, there is a strong need for a technique that is able to compensate for the energy loss and correct for the wavelet distortion. Gabor nonstationary deconvolution was developed in the field of Seismology to compensate for attenuation loss, correct phase dispersion, and produce images with high resolution. In this study, the Gabor algorithm is proposed to deal with the nonstationarity in EM wave propagation and attenuation. Gabor deconvolution is essentially based on the assumption that the anelastic attenuation of seismic waves can be described by a constant Q theory. We investigate the Q characterization of EM wave propagation, the frequency-dependency of EM Q, and the effectiveness of Gabor deconvolution to deal with high loss and dispersion. To accommodate for the EM application conditions, several adjustments are made to the proposed algorithm. Our test results indicate that Gabor nonstationary deconvolution is able to sufficiently compensate for attenuation loss and correct phase dispersion for EM waves that propagate through lossy and dispersive media.

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.