A hybrid optimization method that synthesizes coupling matrices for cross-coupled microwave filters is presented. This method consists of a general solvopt algorithm and fmincon algorithm, respectively. To avoid divergence from the coupling matrix, two cost functions are built, where the first one is constructed from the eigenvalues of the coupling matrix and its principal sub-matrices, while another one is dependent on the determinant of the coupling matrix and one of its cofactors. The values of non-zero elements of the coupling matrix serve as the independent variables to minimize the cost functions by using solvopt and fmincon. Although the stochastic initial values are not sufficiently close to the global optimum, the hybrid optimization procedure is still robust to find multiple coupling matrices to overcome the initial problem. It is significant that the suitable coupling matrix can be chosen from the multiple solutions to meet the given requirements in practice. For demonstrating the proposed hybrid optimization algorithm, some extraordinary prototype topologies are provided which validate the efficiency of the proposed synthesis procedure.

In this paper, we propose to realize ultra-wide-band absorber (UWBA) based on anomalous refraction/reflection of phase gradient metasurfaces(PGM). To achieve high absorption and meanwhile keep small thickness at low frequencies, PGM is incorporated into conventional magnetic materials (MM). The absorptivity is increased due to prolonged propagation length in the MM, which is produced via anomalous refraction/reflection mediated by the PGM. Three typical composite configurations of PGM-based absorbers are investigated and an UWBA design method is finally formulated. Due to small thickness and ultra-wide bandwidth, such absorbers possess great application potentials in EM protection, RCS reduction, etc.

In this paper, an efficient mode reduction technique for eigenmode expansion method is developed to analyze 2-D waveguide grating structures which are a special class of piecewise uniform waveguides. To take advantage of the periodicity property of the structure, the eigenmode expansion method (EEM) is used with the scattering matrix method and a recursive-doubling procedure. In this situation, our proposed mode reduction technique achieves a significant speedup for gratings with large number of periods. Comprehensive numerical examples on the waveguide gratings are studied to validate the efficiency of our proposed mode reduction technique.

This paper introduces a new method for the design and realization of two monopulse antennas with circular polarization and unique phase center for two different frequency bands. The design uses compact sequential-rotation serially fed 2×2 patch array for each section of the monopulse antenna for X band at 8.2 GHz and a patch for S band at 2.25 GHz. The patches are placed on one layer, and the monopulse network and feeds are placed on different layers. The antennas use sequential rotation serial feeds with four and three probes for X band and S band, respectively. Also, the packaging and coupling effects are considered and compensated for this design. Finally, the antenna with a compact multi-layer structure is fabricated, and the simulation results are validated. The bandwidth of X band monopulse antenna system is at least 12.7% in simulation and 10% in fabrication, and it is about 10.2% and 10.3% for S band in simulation and fabrication, respectively. While the phase centers of both frequency bands are approximately at one point, the antenna system can be employed as a feed for reflectors.

This paper describes a monopole antenna with dual-band switchable circular polarization (CP) sense in WLAN and WiMAX bands. The proposed antenna consists of a rectangular patch fed by a microstrip line and a ground plane embedded with a T-shaped slot integrated with PIN diodes. The slotted ground is capable of exciting CP sense around 2.45 GHz for WLAN and around 3.4 GHz for WiMAX, respectively. Two triangular strips are added to improve impedance matching. The CP sense of the proposed antenna can be reconfigured between the right-handed circular polarization (RHCP) and left-handed circular polarization (LHCP) by switching the states of PIN diodes in the slot. The lower band 3-dB axial ratio (AR) bandwidth is 8.6%, and the upper band 3-dB AR bandwidth is 20.8%, in which the return loss is less than -10-dB. Simulated analysis and measured results are carried out and good agreement is achieved.

A novel broadband circularly polarized slot antenna with a rotated slot for bandwidth enhancement is proposed. The antenna has a simple structure, consisting of a microstrip feed line, a substrate, and a rotated rectangular slot with two branches etched on the plane. By appropriately adding the rotated rectangular slot and two branches on the ground-plane, the impedance bandwidth of the antenna is enlarged, and its wide axial-ratio (AR) bandwidth is achieved. Experimental results show the proposed antenna has good right-hand circular polarization (RHCP) characteristics. The measured -10-dB return loss impedance bandwidth and 3 dB axial-ratio bandwidth are 38.8% (1.5 GHz~2.2 GHz) and 25.6% (1.56 GHz~2.02 GHz) at the center frequency of 1.8 GHz.

This work presents experimental investigations of three-dimensional (3-D) far-field holographic microwave imaging (HMI) method for diagnosing inclusions within dielectric objects, and in particular, it relates to electromagnetic imaging to reconstruct dielectric properties of inhomogeneous, lossy bodies with arbitrary shape. The apparatus is designed for operation at a single frequency of 12.6 GHz. 16 antennas are located on a 2-D array plane which is placed under the object in the far-field region, with air in the space between the antenna array and the object. Experimental results indicate that the 3-D HMI system has the ability to produce a 3-D image of multimedia dielectric object and detect small inclusions embedded within an object. The invention has potential application to tissue imaging.

The aim of this work is to miniaturize a microstrip patch antenna resonating at 3 GHz. For this purpose, defected ground structure (DGS) has been employed to shift the resonance frequency of an initial microstrip antenna from 5.7 GHz to 3 GHz by disturbing the antenna's current distribution. The proposed DGS is incorporated in the ground plane under the patch antenna to improve its performances. Finally, a miniaturization up to 50%, with respect to the conventional microstrip antenna, is successfully accomplished. A prototype of the antenna was fabricated with the FR4 substrate and tested. The measurements results were in good agreement with simulation results.

A 12-element triangular-grid rectangular radial line helical array antenna is proposed and investigated. The major characteristic of this antenna is that its radiation elements are arranged in triangular-grid, which is helpful to reducing the number of elements demanded for a certain antenna aperture and grating lobe suppression capacity. The radiation element is optimized to facilitate the manufacture. The feed system with six different groups of output ports is designed to obtain equal-amplitude output using three kinds of probes. An antenna prototype with the center frequency of 2.856 GHz is simulated and measured. In the range of 2.75-2.95 GHz, the experimental result shows an antenna VSWR below 1.2, an antenna gain over 16.3 dB, and an aperture efficiency more than 80%. The field distributions of this antenna are analyzed through simulation, which prove its advantage of high power-handling capacity. Its ability to be used as a sub-array is also demonstrated by forming a 48-element array antenna.

This paper deals with the computation of vibrations and noise of electromagnetic origin for `U'-shaped stator core flux switching permanent magnet (FSPM) machines. The investigation concerns a family of FSPM stator/rotor configurations with 12 slots and 10, 11, 13, and 14 rotor poles. More precisely, the study focuses on the influence of different number of rotor poles on the sound power level of U-core FSPM machines. Electromagnetic forces acting on the stator frame inner surface are calculated with the Maxwell stress tensor thanks to 2-D finite element (FE) simulations. The local magnetic force density serves then as a boundary condition to the 3-D finite element vibrational simulations of the whole stator frame with housing. Finally, obtained displacements help the authors to conduct the acoustic computations using a dedicated 3-D FE analysis model. The obtained vibro-acoustic spectra help electric machines designers to make appropriate choice of stator/rotor pole combination with respect to specifications at early stages of the design process.

The realization of slow light with ultra-flat dispersion in hybrid photonic crystal (HPhC) waveguide is systematically investigated. Metal strips have been introduced to the photonic crystal (PhC) waveguide. The dispersion of the odd mode is commendably flattened in the leaky region. Ultra-flat-band slow light with nearly constant average group indices of 192 over 2 nm (i.e., 330 GHz) bandwidth is achieved. Flexible tuning for the ultra-high group index can also be achieved while keeping the normalized delay-bandwidth product fairly high. The introduction of the metal strips is further demonstrated to help reduce the azimuthal angle of the farfield and provide a high coupling efficiency.

A method for calculating the Casimir force between large, complex 3D objects is presented. Difficulties have previously arisen in broadband multiscale calculation using CEM methods. To expand the range of problems that can be calculated, we use an integral equation, domain decomposition method (DDM) and argument principle to derive the Casimir force formula. The broadband integral equation DDM, which is the augmented equivalence principle algorithm (A-EPA), allows for an efficient broadband solution of large, complex objects. A-EPA subdivides a complex problem into separate smaller subproblems that are later recombined into a reduced matrix. This yields a reduced number of unknowns for complex structures making them feasible with modest computer resources. We demonstrate the advantages of the A-EPA by simulating large, finite, 3D, unaligned corrugated plates, which have previously only been modeled approximately as infinite plates using 2D techniques.

The airborne or vehicle-based SARs are very vulnerable to the influences of airflows or road conditions so as to deviate from the predicted trajectory, which undermines the uniformity of the azimuth sampling. As a result, the SAR image quality can get impaired in varying degrees. Since the SAR systems are sensible to the track deviation, the motion compensation (MOCO) algorithms are always applied as pre-processing of SAR raw data. In this paper, mainly with regard to the motion error caused by the forward velocity variation, a `resampling MOCO' algorithm is proposed as an auxiliary of the widely used bulk MOCO. The simulation result has verified that the performance of the fundamental bulk MOCO algorithm is greatly improved utilizing the proposed method.

Eddy current test has been widely used in many fields because of its simplicity and robustness. In this paper, numerical simulations based on the finite-difference time-domain method were carried out to validate if the eddy current coil can effectively be used in the logging while drilling system. The simulation results showed that the impedance of the eddy current coil is a function of conductivity of the surrounding media. The formation conductivity is strongly dependent on the concentration of hydrocarbons, so different formation layers can be distinguished by measuring coil impedance. Different source frequencies were applied, and it was found that this method works well in frequency range from 100 MHz to 1 GHz. The investigation depth was studied in this paper, and a 3-layer formation model was simulated in this paper. The results showed that this novel method could be effectively used in a well logging system.

An analysis of quasi-optical unstable Bessel-Gauss resonator (QOUBGR) at millimeter wavelengths is presented in this paper. The QOUBGR, formed by a conical mirror and a convex mirror, is designed on the basic of quasi-optical theory and techniques. For the purpose of precisely analyzing the designed QOUBGR, a new algorithm known as iterative dyadic Green's functions (IDGF) is proposed, which originates from famous Fox-Li algorithm. The IDGF algorithm can calculate not only two-dimension (2-D) but also three-dimension (3-D) resonating modes in the cavity. Simulation results demonstrate that the designed QOUBGR can steadily support both zero-order and high-order resonant modes that are approximations to Bessel-Gauss beams. These beams will find their promising applications in the MM- and/or quasi-optical imaging and measurement systems.

This paper presents a comparative study of rectangular base desktop shaped broadband patch antenna (Antenna1) and triangular base desktop shaped broadband patch antenna (Antenna2). Apart from base dimensions all parameters of both antennas are constant. The broadband characteristics are achieved by introducing two parasitic ground planes and notches are etched on the radiating patch. Both antennas are simulated, fabricated and tested for obtaining the desired performance. The designed Antenna1 shows bandwidth of 39.97% (4.95 GHz to 7.42 GHz) whereas an improved bandwidth of 49.0% (4.53 GHz to 7.47 GHz) is achieved through Antenna2. Further, gain and radiation pattern of the two antennas are compared and discussed. The effect of inclination angle `α' on Antenna2 characteristics in obtaining the improved bandwidth is also studied. The proposed antennas are simulated, and results are verified experimentally.

In this paper, the problem of predicting the parameters (positions and magnetic moments) of an Equipment Under Test (EUT) composed of a magnetic dipole and quadrupole is studied. Firstly, a multiple magnetic dipole and quadrupole model (MDQM) is developed to simulate the magnetic behavior of the EUT. The parameters of the model are calculated using the values of the near field measurements applying the Particle Swarm Optimization (PSO) algorithm. For the evaluation of the method, extended simulations were conducted, producing theoretical values and distorting them with noise, and then the developed algorithm was used to create the proper MDQM. As an evaluation criterion, the relative difference between the theoretical and the MDQM's magnetic field is considered.

A dual circularly polarized (CP) antenna is proposed in this paper. By employing suspended strip line to feed the patch at the two diagonal positions with 90º phase difference, single circular polarization is firstly obtained. Then dual circular polarization is excited by an L-shaped strip. The two feeding ports near the edges of the L-shaped strip arms provide the conversion between left-hand circular polarization (LHCP) and right-hand circular polarization (RHCP). Measured results show that the proposed antenna has 10-dB return loss bandwidth of 30.5% (2.08-2.83 GHz), 10-dB isolation bandwidth of 15.7% (2.29-2.68 GHz), 3-dB axial ratio (AR) bandwidth of 25.1% (2.16-2.78 GHz).

Modern electrical and communication technologies benefit from classical electrodynamics and electric circuits, both of which are based on the Maxwell's equations. Using the property of metric invariance in Maxwell's Equations, transformation optics has been proposed and achieves a rapid progress in the past decade. Transformation optics is a method for the conceptual design of complex electromagnetic media, offering opportunities for the control of electromagnetic waves. In this paper, we introduce the general theory of transformation optics and discuss the recent development on the transformation devices in the microwave band, such as non-singular invisibility cloak and its realization in dc circuit, three-dimensional ground-plane cloaks, flattened Luneburg lens, high-performance antennas, and high-resolution imaging lens. Some of the transformation-optics-based devices are expected to have further impact on the microwave engineering applications.

Assessment of biodiversity of pollinators on the landscape scale or estimation of fluxes of disease-transmitting biting midges constitutes a major technical challenge today. We have developed a laser-radar system for field entomology based on the so called Scheimpflug principle and a continuous-wave laser. The sample-rate of this method is unconstrained by the round-trip time of the light, and the method allows assessment of the fast oscillatory insect wing-beats and harmonics over kilometers range, e.g., for species identification and relating abundances to the topography. Whereas range resolution in conventional lidars is limited by the pulse duration, systems of the Scheimpflug type are limited by the diffraction of the telescopes. However, in the case of sparse occurrence of the atmospheric insects, where the optical cross-section oscillates, estimation of the range and spacing between individuals with a precision beyond the diffraction limit is now demonstrated. This enables studies of insect interaction processes in-situ.