A compact stacked Yagi antenna is proposed with bandwidth enhancement in this paper. To reduce the size of the antenna and simultaneously improve the front-to-back ratio (FTBR), a reflector, modified with six slots, two λ0/4 meanderline-shaped slots and four straight short slots, is employed. Furthermore, a ladder-like director is designed to overcome the mismatch loss caused by the diminution of the height between the reflector and driven dipole. As shown in both simulation and measurement, the proposed compact Yagi antenna can achieve a compact size of 0.55λ0×0.55λ0×0.08λ0, |S11| ≤ -10 dB bandwidth of 17.2% and an FTBR of 22dB at 2.2GHz. The acceptable results make the proposed Yagi antenna a good candidate for applications where compact size and wide bandwidth are needed.

In this paper, the direction of arrival (DOA) and polarization parameters are estimated by a uniform circular array (UCA) with several single-polarized sensors. An ecient and improved polarization MUSIC algorithm for estimating the DOA and polarization parameters is presented. This method uses information on the amplitude to reduce the computational complexity. When the source is linearly polarized, the proposed algorithm is more accurate at a low signal-to-noise ratio (SNR). Monte Carlo simulations verify the ecacy of the proposed method.

To enhance the gain of conventional Vivaldi antenna (CVA), a novel dielectric sheets-covered Vivaldi antenna (DSCVA) is proposed. The dielectric sheets suck energy from the tapered slot region and flare termination region of the CVA, and thus act as surface wave antennas to improve end-fire performances. The CVA, DSCVA as well as the DSCVA with elongated tapered profile (SP-DSCVA) are designed, fabricated and measured. The simulation results are in good agreement with the experimental data. Measurement results show that the gain increase of the DSCVA is up to 5.1 dBi in the range of 3.5-16.5 GHz without increasing antenna length compared to the CVA. More gain enhancement is achieved for the SP-DSCVA. In addition, the half power beamwidths of the CVA as well as the sidelobe levels are improved in both E- and H-planes.

In this paper, a hybrid algorithm of binary lightning search algorithm and simulated annealing (BLSA-SA) is proposed to optimize the design of multilayer microwave absorbers for normal incidence. The multilayer absorber is designed to find a set of coatings that minimize the reflection coefficient over the desired frequency. The design problem is translated into solving the binary problem. Three different design examples are presented to verify the performance of the BLSA-SA. The results show that the reflection coefficient and thickness of BLSA-SA are better than those of other heuristic algorithms for multilayer absorber design. In the five-layer design, the standard deviation of BLSA-SA is the smallest among the 20 independent test results of the algorithms, which indicates that the BLSA-SA algorithm, has a strong stability.

This paper presents a Quad-Rectangular Shaped Microstrip Antenna (QRSMA) fed by a single microstrip line feed. QRSMA having different frequency bands is designed to be applied to L(1-2GHz), S(2-4GHz) and C(4-8GHz) bands applications. QRSMA is loaded with a single square patch and 4 rectangular patches. The patches are loaded using a flame retardant substrate (Fr-4). The patches are connected with 1 mm width of copper (Cu) stripline. Thus the proposed design of patches and width is responsible for desired multiband operations. The antenna resonates at frequencies f1=1.074, f2=3.119, f3=4.089, f4=5.683 and f5=6.514 GHz. Thus, the antenna is useful in the L, S and C band applications. Compared to other antenna designs, the proposed antenna exhibits multiband performance, size reduction and is economical. It also realizes tunability of frequencies having stable radiation pattern with compact electrical size. The paper analyses the simulated and experimental results. Various cases of QRSMA performances are also compared in this paper.

In this study, the misalignment of bistatic clutter spectral centers is considered, and an efficient adaptive main-lobe clutter compensation approach is presented for mitigating the bistatic geometry-induced clutter dispersion. In order to reduce computational load, an improved orthogonal matching pursuit (OMP) is introduced into the space-time clutter spectrum estimation. This method can accurately extract the required parameters for compensating the clutter spectral centers misalignment via sparse reconstruction with the desired Doppler cells. Simulation results are presented to demonstrate the effectiveness and efficiency of the proposed method.

In this paper, an asymmetric thrust magnetic bearing (MB) design principle and method are introduced. Different from the general design method of magnetic bearing, the asymmetric magnetic bearing design method focuses on the effect of asymmetric factor. A permanent magnet biased asymmetric hybrid thrust magnetic bearing (AHTMB) with secondary air-gap is designed in detail. A multi-objective optimization is conducted with genetic algorithm (GA) to get smaller mass and less loss. According to optimized model parameters, magnetic field distribution, stiffness and effect of asymmetry factor on stiffness are also analyzed. For stability of the system, equivalent stiffness and equivalent damping and current characteristics are deduced. Based on the analysis results and design methods, appropriate asymmetry factor asymmetric can be chosen to satisfy the different bias force requirement. With small number of coils and current, AHTMB with secondary air-gap is beneficial for decreasing the copper loss and enhancing dynamic performance of control system.

A subject of plasmonic spinphotonics is developed for surface plasmon polaritons (SPPs). Since an electromagnetic field is a vectorial field, it has spinning angular momentum, and thus spin current is one of its degrees of freedom. A spin current density tensor has 24 independent components because of its antisymmetry in coordinate indices. By using the law of conservation of electromagnetic angular momentum (i.e., orbital angular momentum plus spinning angular momentum), the electromagnetic spin current density tensor is derived, and its characteristics are indicated. Since surface plasmon polaritons can exhibit various intriguing optical and electromagnetic effects and have many practical applications, we consider a new potential effect relevant to spin current transfer. The electromagnetic spin current density tensor and its intensity profile are analyzed for SPPs sustained on a metal-dielectric interface. The plasmonic spin on a metal ring and a straight thin metal belt is calculated, and based on this, a nanomechanical effect caused by plasmonic spin current transfer is suggested. It is expected that such a nontrivial nanomechanical effect will be useful in the design of new nanophotonic devices aiming at sensitive, accurate measurement techniques.

A compact Ku-band bandpass filter (BPF) with wide pass-band, compact size and high selectively is presented. The presented BPF is composed of two quarter-wavelength resonators and a dual-mode resonator, resulting in a compact circuit size. The transmission zeros (TZs) located at the lower and upper stopband are achieved by the mixed electromagnetic (EM) coupling and dual-mode resonator, respectively, resulting in a high frequency selectively. The measured results show minimum in-band insertion loss, fractional bandwidth and variation of group delay to be 0.9 dB, 36.2% and 0.12 ns, respectively. Also, the stopband suppression is greater than 28 dB from 5 to 10.3 GHz and 30 dB from 19.5 to 29.5 GHz. The effective circuit size of the filter is 8.43×2.28 mm² (0.63 λg ×0.17 λg, where λg is the guide wavelength of 15.1 GHz.)

The configuration of an infinite planar conductive shield is examined when it is excited by an electromagnetic near field generated by a coil current source as that of a wireless power transfer (WPT) system. The analytical expressions of the electromagnetic field based on the transmission theory of shielding are given for different frequencies and different incidence angles of the near field generated by the coil current, assuming the conductive planar shield placed in the close proximity of the coil. The obtained results are discussed and compared with other traditional analytical and numerical solutions.

Based on convoluted interwoven element, a miniaturized frequency selective surface (FSS) with stable band-stop response is proposed in the paper. By extending the four dipoles into the adjacent elements, the equivalent inductance and capacitance are increased, and therefore the proposed FSS realizes promising miniaturization characteristics. The simulation results indicate that the resonant frequency is 1.19GHz, and the dimension is only 0.027λ0. Compared to traditional crossed elements, the size is reduced by 94.6%. Besides, the FSS has excellent angle-stability under both TE and TM waves. Finally, the proposed FSS is fabricated and measured, and the experiment results prove the satisfactory consistency with the simulation results.

This paper presents our research work on designing a dual-band dual-polarized (DBDP) series-fed S/X-band shared aperture antenna (SAA) for synthetic aperture radar (SAR) applications. The proposed SAA DBDP X-band antenna is designed with the concept of series-fed 4-group 2x2 planar arrays with high impedance microstrip line feeding in both vertical and horizontal polarizations. By etching out the inner edge elements from 2x2 X-band subarrays in all the four-groups, the S-band element could be accommodated. The design evolution stages have been presented. The S-band (3.2GHz) is best suited for volumetric soil moisture estimation using SAR and X-band (9.3 GHz) best suited for surveillance SAR applications and grain size estimation. To verify the antenna design concept, a prototype is fabricated and measured with both S-parameters and radiation characteristics including gain measurements. The antenna with reflection coefficient lS11l < -10 dB has an impedance bandwidth 3.12-3.42 GHz (9.3% BW) in S-band and 9.2-9.36 GHz (1.72% BW) in X-band. The measured isolation lS21l between two different bands in the same polarization is better than 25 dB, and the isolation between two different bands in two orthogonal ports is better than 30 dB. Measured gain of the antenna at S-band is better than 8.5 dBi at V-port and H-port, and X-band is better than 11 dBi at either port. Measured side-lobe level (SLL) at S-band is better than -17 dB at either port, and X-band is better than -20 dB at either port. The overall size of the S/X-DBDP SAA is 100 x 100 x 1.6 mm³. Measured results of the S/X-DBDP SAA show good agreement with the finite integration technique (FIT) based computer simulation technology (CST) microwave studio.

The power flow for electromagnetic wave absorbers consisting of pattern conductor layers acting as frequency selective surfaces, absorption layers, and short circuit layers was investigated by Poynting vectors. A method was developed to evaluate the flow of electromagnetic wave power by an electromagnetic wave absorber upon irradiation with electromagnetic waves. The results indicate that the electromagnetic wave absorption phenomenon involves generation of true power, a real part of the time averaged Poynting vector, which moves horizontally along the pattern surface after the incident wave has irradiated the pattern conductor from the vertical direction, and the direction of power flow changes to enter the polymer layer from the pattern interval, causing an accumulation of power inside the polymer layer, followed by absorption, which is converted into heat due to the loss factor.

Phantoms provide valuable test platforms for developing medical devices. Solid materials in particular allow fabrication of stable and robust models. This paper presents a novel, anatomically realistic, multi-layered head phantom made from dielectrically accurate, stable, easily mouldable, low-cost tissue-mimicking materials for testing of microwave diagnostic systems. Also incorporated is a mechanism for inserting reconfigurable lesions and a novel circulatory system modelling physiology. Tissue-mimicking materials composed of graphite, carbon black, and polyurethane with small volumes of acetone or isopropanol were fabricated and dielectric properties were measured across the 1 - 8.5 GHz band. The tissuemimicking material properties were adjusted until their dielectric properties matched those of reference values for target tissues of interest, thereby emulating: weighted aggregates of head tissues external to the brain, tissues comprising the brain, and blood. 3D printed anatomically realistic head and brain moulds cast the phantom mixtures for each layer. Cylindrical holes in the brain layer allow insertion of pathological lesion phantoms, such as haemorrhages. Tubing embedded in the brain layer forms a symmetrical loop providing a novel simplistic model of circulation. The resulting head phantom is anatomically realistic, dielectrically stable, enables pathology modelling, and has, uniquely, a circulatory loop. This novel head phantom provides a valuable test platform for microwave diagnostic studies.

In this paper, off-grid DOA estimation based on sparse representation and Rife algorithm is presented to improve performance when the sparse signal directions are not on the predefined angular grids. The algorithm is divided into two steps. Firstly, the real-valued sparse representation of array covariance vector (RV-SRACV) algorithm is used to do off-grid DOA estimation, and it does not need to estimate the noise power. Secondly, Rife algorithm is used to correct the DOA estimation, and after that the DOA can be accurately estimated. The effectiveness and superior performance of the proposed algorithm are demonstrated in the simulation results.

The least square method has been widely applied in many fields. However, while the approach is used for antenna array pattern synthesis, it is not excellent. In this paper, the least square is used to synthesize antenna array pattern and its performance is reviewed. Then contraposing to the shortcoming of the least square method, a new steerable least square(SLS) method is put forward. For an antenna array whose manifold matrix has been determined, the projection matrix equation can be derived from array manifold matrix easily. In order to get premium solution of array element excitation, a novel projection matrix equation with adjustable matrices is adopted. The results of simulations show that the pattern synthesized by the traditional least square method fits the targeted pattern badly and is worse in the key performance indicators of main-lobe width, peak level of side-lobe and null beam level than the targeted pattern; however, the pattern synthesized by the new SLS method fits the targeted pattern well in zero point and local peak distribution and is better in the key performance indicators of main-lobe width, peak level of side-lobe and null beam level than the targeted pattern.

In this paper, a compact multiple-input-multiple-output (MIMO)/diversity antenna with WLAN band notch characteristics, high isolation, and good ECC suitable for portable ultra-wideband (UWB) applications is presented. The proposed antenna has optimized dimensions of 29 mm × 38 mm. The antenna consists of two orthogonal circular monopoles with a 50 Ω microstrip feed line. In addition, to enhance the impedance bandwidth, a fractal slot, created using Minkowski fractal geometry, is introduced into the ground plane, which is located on the other side of the substrate, just below the feed line. Good isolation (≥ 21.5 dB) with a fractional bandwidth up to 220% is achieved between antenna elements by introducing two ground stubs and a rectangular slot in the ground plane. A band-notch characteristic in the WLAN band is obtained by etching an elliptical split-ring resonator (ESRR) in the radiator. Moreover, a diversity performance of the antenna in terms of ECC (<0.01) and capacity loss (<0.3 b/s/Hz) is performed. This paper offers, for the first time, a combined effect of fractal geometry and ESRR geometry in an antenna design. Finally, a comparison of the proposed antenna is performed with the UWB MIMO/diversity antennas existing in the literature. These results show the suitability of the presented antenna for portable UWB systems.

A new low cost method for implementing an Instantaneous Frequency Measurement (IFM) system is presented in this paper. The proposed method is based on dividing the incoming RF signal into four signals and filtering each one by an appropriate band-pass filter. The frequency is then estimated from the power level of the filtered signals. A closed form for the Standard Deviation (STD) and the bias of the frequency estimator is derived. A design example for an IFM system with a working frequency band of 2 to 4 GHz is presented with simulated and measured results. The design is implemented on a commercial FR-4(DE104) substrate using printed circuit board technology. Experiments in a laboratory show a maximum error of about 15 MHz in estimating the frequency value.

The use of transverse circular representation in circular cylinder coordinate system provides an alternative approach to the solution for vector Helmholtz partial differential equations (VH-PDE) of electromagnetics. After separation, VH-PDE for electric (magnetic) field splits into a set of three ordinary differential (Bessel) equations for two opposite transverse circular polarizations (TCP) and the axial component. The approach is suitable for solving the problem of cylindrical waveguides and cavities starting from the transverse fields. The coupling between TCP fields via the axial component affects nonreciprocal propagation in waveguides. The procedure is illustrated on a dielectric waveguide. It may be extended to the media with circular eigen polarizations including those displaying magnetooptical Faraday effect or optical activity.

This paper presents a dynamic modelling of a series of induction motors (IM) squirrel cage with different shapes of rotor deep bars taking into account the skin effect. The approach is divided into two parts. The first part consists in modelling the skin effect in a rectangular rotor deep-bar with three methods (conventional analytical method, nite element method and analysis method of circuit). These are compared (estimate of the relative error), and subsequently, generalized to more complex forms (trapezoidal, inverted, direct trapezoidal and double cage), done by using the two last methods which take into account the geometrical non-linearity of the slots. The second part consists in a dynamic modelling with variable parameters that take into account the skin effect, simulated for a series of motors with the same power (with different geometric shapes of rotor bars), to see their influence on the starting characteristics of these IM, and the results are compared and discussed.