In this paper, a novel pattern reconfigurable microstrip parasitic array is proposed, which is similar to the microstrip Yagi antenna. The antenna is printed on a dielectric substrate and has a probe feeding center strip with two parasitic strips on both sides of a higher plane. The driven patch is equipped with four RF PIN diodes by which we can change the antenna's state and vary its frequency at 2.1 GHz, 2.4 GHz and 2.6 GHz respectively. Each of the parasitic patches is equipped with six switched connections symmetrically which is utilized as a director or a reflector for pattern reconfiguration. Compared with conventional antenna, the proposed antenna combines both radiation pattern reconfiguration and frequency reconfiguration together, and by raising the plane of the dielectric substrate of the parasitic patch, the tilt angel of this antenna's maximum radiation direction is lager and the gain is higher.

Time-of-flight (TOF) has been used to estimate sound velocity (SV) distribution of heterogeneous tissue to relieve the effect of acoustic heterogeneity in microwave-induced thermo-acoustic tomography (MITAT). Accurately picking the TOFs is significantly important to ensure high accuracy SV images, which greatly help to reconstruct the microwave absorption distribution accurately. However, current methods for picking the TOFs are designed for single source case. For breast tumor detection in MITAT, these methods become ineffective or even fail at the situation where multiple tumors are embedded in a normal breast tissue. In order to accurately reconstruct the microwave absorption properties of tumors in heterogeneous tissue in MITAT, an efficient method for picking tumors' TOFs is proposed. Combining the advantages of the wavelet transform and Akaike information criterion (AIC), the proposed method introduces a concept of separate extraction of TOFs. It can efficiently and accurately pick the TOFs of different tumors from the measured data in MITAT. Using the TOFs picked by the proposed method can efficiently help to reduce the effect of acoustic heterogeneity and greatly improve the accuracy and the image contrast of reconstructed microwave absorption properties. Some numerical simulations are given to demonstrate the effectiveness and feasibility of the proposed method in this paper.

Due to their very high integration density, echelle grating spectrometers based on silicon nanophotonic platforms have received great attention for their applications in many areas, such as optical sensors, optical communications, and optical interconnections. The design of echelle gratings requires an effective modeling and simulation technique. Though we have used a boundary integral method to accurately analyze the polarization-dependent performance of the echelle grating, it is complicated and time-consuming for the simulation due to its large size and aperiodic structure. In the present paper, we will present a faster simulation method for the grating with twice total internal reflection facets based on a modified Kirchhoff-Huygens principle with the influence of the Goos-Hachen shift considered. On the one hand, the presented simulation results agree well with our previous results obtained by the boundary integral method when the shift can accurately be calculated using a FDTD method. On the other hand, the biggest advantage of the new method over the existing methods is that it can also provide an insightful physical explanation for many numerical results. Finally, we will effectively apply the present method to design an on-chip spectrometer with very low noise floor.

An accurate and efficient SAR raw data generator is of considerable value for testing system parameters and the imaging algorithms. However, most of the existing simulators concentrate on the raw signal simulation of the static extended scenes and targets. Actually the raw signal simulator of the moving targets is highly desired to quantitatively support the application of the ground moving targets indication. The raw data simulation can be exactly realized in the time domain but not efficient especially when simulating an extended scene. As for the issues, the analytical expression for the 2-D signal spectrum of moving targets with constant acceleration is derived and a fast raw data simulation method in the 2-D frequency domain based on inverse ω-k algorithm is proposed in this paper, where the inverse STOLT interpolation is applied to simulate the range-azimuth couple. So it is more efficient than the time domain one by making use of Fast Fourier Transform (FFT). Simulation results for a man-made scene and a real SAR scene are provided to demonstrate its validity and effectiveness.

In this paper, we propose a new method for Synthetic Aperture Radar (SAR) image despeckling via L₀-minimization strategy, which aims to smooth homogeneous areas while preserving significant structures in SAR images. We argue that the gradients of the despeckled images are sparse and can be pursued by L₀-norm minimization. We then formularize the despeckling of SAR images as a global L₀ optimization problem with ratio-of-average operations. Namely, the number of pixels with ratio-of-average that are unequal to one is controlled to approximate prominent structures in a sparsity-control manner. Finally, a numerical algorithm is also employed to solve the L₀ optimization problem. In contrast with existing SAR image despeckling approaches, this strategy is applied without necessity to consider the local features or structures. The performance of our method is tested on high resolution X-band SAR images. The experimental results show the effectiveness of the proposed method in SAR image filtering. It outperforms many typical despeckling techniques in terms of the equivalent-number-of-looks and the edge- preserve-index. It also has some advantages compared with the existing state-of-the-art despeckling filters.

A near-field three dimensional imaging algorithm for circular SAR is proposed in this paper. It adopts the theory of spherical wave decomposition to transform Green function to a superposition of plane wave components. Using this relation, the image-reconstruction can be implemented in frequency domain instead of in spatial domain, which simplifies the solving process of target reflectivity function, and allows for the target to be near to the radar. Through compensating phase factor and filtering at each elevation, we firstly get the ground CSAR signal of each elevation in frequency domain. Then, performing two dimensional inverse nonuniform fast Fourier transform and accumulating the results of all azimuth angles, the reconstructed two dimensional image corresponding to an elevation is achieved. Finally, using reconstructed image datum of all elevation, the three dimensional image of target is obtained. To demonstrate the imaging performance of our method, numerical simulations and experiments are conducted. By comparing the results with the focusing operator algorithm and the back-projection algorithm, it is found that the proposed algorithm is more efficient and can obtain a good imaging performance.

Damage on rail increasingly originates from the surface of the rail as a result of for example rolling contact fatigue (RCF). This is a major concern for track operators, who operate test regimes for flaw detection and monitoring. The paper aims to assess the feasibility of applying electromagnetic (EM) simulation techniques to high frequency magnetic induction sensing of flaws in a section of rail head using the Boundary element method (BEM). When the driving frequency is significantly high (~MHz), the rail with high conductivity can be treated as perfect electric conductors (PEC) with negligible errors. In this scenario, BEM based on scalar potential and integral formulations becomes an effective way to analyze this kind of scattering problems since meshes are only required on the surface of the object. A simple high frequency magnetic induction sensing system was chosen to inspect the surface flaw of the rail. Different kinds of flaws were tested with different sensor configurations. The simulations were carried out using an algorithm the authors have developed in MATLAB. The paper provides new insights into the application of magnetic induction sensing technique using BEM in non-destructive testing. Based on the simulation and mathematical analysis, hardware system can be built to verify the proposed detection strategy.

In this paper, a novel approach was used to design two-layer stacked high gain microstrip antenna array with improved bandwidth and high aperture efficiency. Cross Snowflake fractal microstrip patches were employed as radiation elements. Varieties of antenna arrays with different fractal iterations were optimized by using the Genetic Algorithm (GA) associated with 3D full-wave Finite Element Method (FEM) in order to investigate the influence of the Cross Snowflake fractal radiators. As compared with the conventional square patches, the Cross Snowflake fractal configuration provides extremely high flexibility to achieve a wideband performance and maintains higher aperture efficiency at operating frequency band. A prototype antenna with 2 x 2 Cross Snowflake radiators was fabricated and measured. Both simulated and measured results show that the proposed antenna has some promising performances to be more specially, the measured impedance bandwidth is 22.9% (from 5.18 GHz to 6.52 GHz) when S₁₁<10 dB; the simulated gain is 12.0 dBi and its corresponding aperture efficiency is up to 87.4% at the working frequency 5.8 GHz.

We report a MEMS (micro-electro-mechanical systems) compatible distributed loss type sever design for the 220 GHz double vane half period staggered traveling-wave tube amplifier (TWTA) [1]. The cold test simulations for a full TWT model including input/output couplers and broadband tapered vane transitions incorporating the sever, predicted a return loss (S₁₁) of < -10 dB in the pass band (205 GHz-275 GHz) while an insertion loss/isolation (S₂₁) of < ~-27 dB. The return loss of the TWT circuit did not degrade by the inclusion of the sever (< -10 dB) while still maintaining a good isolation (S₂₁) for the RF signal. Particle-In-Cell (PIC) simulation analysis for the full 220 GHz TWT circuit (a) without sever and (b) with sever was conducted. With the inclusion of the sever, the TWTA showed generally a stabilized output response for all cases. The maximum power from the long sever case was ~25 W for P_in ~50 mW and the gain was ~27 dB. The reverse power was decreased to ~30 mW. For the short sever, the PIC results were even better with a maximum output power of ~62 W and a gain of ~30.92 dB with a reduced reverse power of ~5 mW for an input power of 50 mW at 220 GHz. The FFT spectrum of the RF signal at the output port also showed a spectrally pure waveform at 220 GHz.

We generalize Wheeler-Feynman electrodynamics with a variational problem for trajectories that are required to merge continuously into given past and future boundary segments. We prove that the boundary-value problem is well posed for two classes of boundary data and the well-posed solution in general has velocity discontinuities, henceforth a broken extremum. Along regular segments, broken extrema satisfy the Euler-Lagrange neutral differential delay equations with state-dependent deviating arguments. At points where velocities are discontinuous, broken extrema satisfy the Weierstrass-Erdmann corner conditions that energies and momenta are continuous. Electromagnetic fields of the finite trajectory segments are derived quantities that can be extended to a bounded region B of space-time. Extrema with a finite number N of velocity discontinuities have extended fields defined in B with the possible exception of N spherical surfaces, and satisfy the integral laws of classical electrodynamics for most surfaces and curves inside B. As an application, we study the hydrogenoid atomic model with mass ratio varying by three orders of magnitude to include hydrogen, muonium and positronium. For each model we construct globally bounded trajectories with vanishing far-fields using periodic perturbations of circular orbits. Our model uses solutions of the neutral differential delay equations along regular segments and a variational approximation for the head-on collisional segments (spikes). Each hydrogenoid model predicts a discrete set of finitely measured neighbourhoods of periodic orbits with vanishing far-fields right at the correct atomic magnitude and in quantitative and qualitative agreement with experiment and quantum mechanics. The spacings between consecutive discrete angular momenta agree with Planck's constant within thirty-percent, while orbital frequencies agree with a corresponding spectroscopic line within a few percent.

This paper presents a new rectangle-slot antenna for ultra wideband applications with 3.5/5.5 GHz dual stop-band characteristics. The antenna contains a simple square radiating patch and a rectangle-slot ground plane, which provides a wide bandwidth from 2.6 GHz up to 14.1 GHz. In order to obtain dual stop-band properties at 3.5 and 5.5 GHz, a rectangularshaped slot is etched off the ground plane, and a strip line ended up a shorting pin is applied, respectively. The antenna is simple in configuration and has a compact dimension of 20×22 mm². The proposed antenna is designed, simulated and fabricated. The measured results exhibit a acceptable agreement with the simulated data. The antenna provides nearly omnidirectional radiation patterns, relatively flat gain over the entire UWB frequency excluding the two stop bands.

A shaped-beam series-fed aperture-coupled stacked patch array antenna at X-band is presented. To improve the array bandwidth, two-port aperture-coupled stacked patch antennas, which are suitable for the series-fed array configuration, are presented as the radiating elements. To offer the pattern design and optimization progresses more flexibility, a uniformly spaced array configuration is applied in the shaped-beam pattern design, instead of the conventional nonuniformly spaced array configuration. The experimental results show that, in a 7.6% bandwidth, the main beam shape of the array maintains in good agreement with the design goal, and the side lobe level maintains lower than -18 dB.

In this paper, the properties of anisotropic photonic band gaps (PBGs) in three-dimensional (3D) nomagnetized plasma photonic crystals (PPCs) composed of anisotropic dielectric (the uniaxial material) spheres immersed in uniform nomagnetized plasma background with various lattices including the diamond, face-centered-cubic (fcc), body-centered-cubic (bcc) and simple-cubic (sc) lattices, are theoretically investigated by the plane wave expansion (PWE) method. The equations for calculating the anisotropic PBGs in the first irreducible Brillouin zone are theoretically deduced. The anisotropic PBGs and a flatbands region can be obtained as the uniaxial material introduced into 3D PPCs. The PPCs with diamond lattices consisting of isotropic dielectric have the larger PBGs compared to PPCs doped by the uniaxial material since its low symmetry structure. Furthermore, the PPCs with fcc, bcc, sc lattices will not exhibit a complete PBG unless the uniaxial material is introduced. The influences of the ordinary-refractive index, extrordinary-refractive index, filling factor and plasma frequency external magnetic field on the properties of anisotropic PBGs for 3D PPCs with fcc, bcc, sc lattices are investigated in detail, respectively, and some corresponding physical explanations are also given. The numerical results show that the anisotropy can open partial band gaps in 3D PPCs with fcc, bcc, sc lattices, and the complete PBGs can be obtained compared to 3D PPCs doped by the conventional isotropic dielectric. It also is shown that the anisotropic PBGs can be tuned by the ordinary-refractive index, extrodinary-refractive index, filling factor and plasma frequency, respectively. The complete PBGs can be obtained by introducing the uniaxial material as 3D PPCs are with high-symmetry lattices. This also provides a way to design the tunable devices.

A radiation pattern synthesis technique for large planar arrays with active element pattern (AEP) method and fine-grained parallel micro-genetic algorithm (FGPMGA) is presented. Based on the AEP method, the mutual coupling between array elements can be taken into account. Analysis problems of large rectangular and triangular grid planar arrays are divided into small linear array problems. And for a multiple concentric circular ring array, we only need to obtain one-sixth of all AEPs. So computational cost is greatly reduced. Large planar arrays with low side lobe level (SLL) can be achieved via optimizing the excitation amplitudes and phases. In order to reduce the global optimization time, the FGPMGA is used. This technique is applied to design 256-element rectangular grid, 200-element triangular grid and 4-circle 60-element concentric circular ring E-shaped patch antenna arrays. The radiation patterns calculated by the AEP method show good agreements with those by using CST Microwave Studio.

Based on the theory of microstrip-to-slotline transition, a series of power dividers using CPW-to-microstrip transition is developed. These power dividers can be made to be coplanar or non-coplanar structure, and the phase difference between the two output ports can be flexibly achieved in phase or out of phase. Two microstrip feed lines couple the energy from the two slots of the CPW with equal magnitude, thus realizing CPW-to-microstrip transition. An in-phase power divider and an out-of-phase one are designed, fabricated and measured. The measured results show that the power dividers provide good return loss, low insertion loss, and stable phase between the two output ports over the operating frequency band.

In this paper, an ultra-wideband (UWB) monopole printed antenna with wing-shaped coplanar waveguides (CPW) feeder is proposed, in which the wing-shaped CPW feeder is used to increase the impedance bandwidth. A CPW-fed antenna is used in this design for its simple structure, compact size and ease of integration with microwave circuits. The proposed antenna is fabricated on Durion Roger R4003c, 22×41 mm² substrate and measured. The simulated and measured results show that the antenna operates between 2.04 to 11.67 GHz. The unique wing-shaped CPW feeding structure causes a significant increase on the bandwidth of the proposed antenna compared to the present patch antennas. Also it removes unwanted ripples from the return loss and improves antenna's pattern.

This paper presents a high-selectivity dual-band bandpass filter with independently-tunable passband frequencies. A tap-coupled structure is utilized to feed the two resonators at lower passband and a coupling structure is used to feed the two resonators at the upper passband. Two pairs of varactor-loaded resonators operating within two different frequency ranges, allow the independent passband frequency tuning. Using this configuration, it is convenient to tune the center frequency of each passband, while the responses of the other passband remain unaltered. Source-load coupling is realized to generate transmission zeros, resulting in high skirt-selectivity. The transmission zeros move synchronously with the passbands, ensuring sharp roll-off rate for all tuning states. To verify the proposed idea, a demonstration microstrip tunable bandpass filter is implemented. The simulated and measured results are presented.

Precise modeling of radio propagation is necessary for experiencing the benefits of wireless technology for indoor environments. Among many modeling techniques, the ray tracing based prediction models become popular for indoor wireless radio propagation characterization. Though the ray tracing models are popular, their key deficiency is the slower performance. In this paper, an accelerated technique for three dimensional ray tracing using Adelson-Velski and Landis (AVL) tree data structure is introduced. Here, the AVL tree data structure is coupled with the concepts of quadrant eliminating technique (QET) and nearest neighbor finder (NNF) for optimization and fast characterization of indoor wireless communication. Surface intersection scheme (SIS) is also introduced for optimizing the ray-object intersection time. The AVL tree is used for the effective handling of the objects and environments relative information. The QET technique decreases the ray tracing time by omitting unnecessary object, while NNF decreases the ray-object intersection time by finding the nearest object in an efficient technique. For the validation of the superiority of the proposed technique, a detailed comparison is made with the existing techniques. The comparison shows that the proposed technique has 81.69% lower time consumption than the existing techniques.

A novel printed monopole antenna covering 2.4-2.484 GHz (Bluetooth), 2.5-2.69 GHz (IMT-E) and 3.1-10.6 GHz (UWB) frequency bands is presented. The entire frequency bands are obtained by a modified U-shaped radiator and a modified ground plane. To prevent possible interference between UWB systems and other existing wireless systems such as WLAN and WiMAX, a SCRLH resonator structure is placed next to the feed line. Characteristics of the Bluetooth and IMT-E bands are further enhanced by two quarter-wavelength strips added on each side of the radiator. The proposed antenna can be easily printed on a 1.6-mm-thick FR4 substrate with dimensions of 30 × 41 mm². Simulation and experimental results show that the antenna yields an impedance bandwidth of 2.3-2.8 and 3-12 GHz with -10 dB reflection coefficient, except for the dual notched bands of 3.2-3.6 for WiMAX and 4.9-6.1 GHz for WLAN. The electrical characteristics in frequency and time domain show suitability of this antenna for use in UWB systems.

Bionics principle is applied to frequency selective surface (FSS) design in this paper. To authenticate the method, a novel bionic and miniaturized FSS is proposed by use of a model of alternate phyllotaxis. The simulated and measured results show that the proposed FSS has a much smaller size and maintains other FSS-related performances. To study the applications of the novel bionic FSS in practice, it is used for the ground plane of an antenna array to reduce the antenna radar cross section (RCS). Compared to a reference antenna, the antenna with bionic FSS has lower RCS and favorable radiation performance. Hence, applying bionics principle to FSS design and antenna RCS reduction is proved feasible, which will serve as a good candidate for the future design of FSS and antennas with or without a requirement of RCS control.