A microstrip based Ultra-Wideband (UWB) Bandpass Filter (BPF) with a notch at WLAN and simultaneously improved stopband till 18 GHz is proposed. Meander shaped Defected Ground Structures (DGS) are used to implement the notch (which can be increased in width and number) within the passband and double U-shaped DGS present under the input and output feeding lines are used to attain the suppressed stopband. Experimental results are in good agreement with the simulated data.

A compact tri-band slot antenna based on a mesh-grid structure, which is suitable for WLAN/WiMAX applications, is presented. The proposed antenna is optimized by a Boolean differential evolution algorithm (BDE). Then an experimental prototype is fabricated and measured. Results of simulation and measurements indicate that the proposed antenna has |S₁₁|<-10dB in the three chosen frequency bands from 2.35 to 2.85 GHz, from 3.1 to 4.4 GHz and from 4.8 GHz to 5.85 GHz, which covers WLAN bands (2.4/5.2/5.8 GHz) and the WiMAX bands (2.5/3.5/5.5 GHz), respectively. In addition, good radiation performances such as omnidirectional and doughnut-shaped directivity and reasonable gain over the operating bands have been obtained. This example also demonstrates the applicability of the BDE/MOM optimization algorithm to efficient and in potential automated method for the antenna design.

This paper presents a method for focusing a moving target in single channel SAR data utilizing a novel technique for range migration correction. The First Order Keystone transform is first applied to remove the range-walk of the moving target signature. A search procedure based on maximizing a contrast cost function is then employed to determine the phase correction which compensates for the remaining range curvature. Finally an adaptive notch filter is used to construct an estimate of the azimuth compression filter necessary to focus the moving target. An experimental result is provided for airborne SAR data to demonstrate the performance of the approach.

A new compact and wide-band waveguide dual circular polarizer at Ka-band is presented and tested in this paper. This compact structure is composed of a three-port polarizing diplexer and a circular polarizer realized by a simple pair of large grooves. The polarizing diplexer includes two rectangular waveguides with a perpendicular H-plane junction, one circular waveguide coupled in E-plane. A cylindrical step and two pins are used to match this structure. For a LHCP or RHCP wave in the circular port, only one specific rectangular port outputs power and the other one is isolated. The accurate analysis and design of the circular polarizer are conducted by using full-wave electromagnetic simulation tools. The optimized dual circular polarizer has the advantage of compact size with a volume smaller than 1.5λ³, broad bandwidth, uncomplicated structure, and is especially suitable for use at high frequencies such as Ka-band and above. The prototype of the polarizer has been manufactured and test, the experimental results are basically consistent with the theories.

This study presents a novel miniaturized dual-band coupled-line impedance transformer. This dual-band matching technique uses the characteristics of coupled-line and dual-band stubs to realize matching arbitrary complex impedance to arbitrary complex impedance at two arbitrary uncorrelated frequencies. Especially, it satisfies the demand of dual-band matching at two relatively closed operating frequencies (n= f₂ / f₁ ≤ 1.2), and occupy a very small circuit area with inherent DC-Block function. The proposed synthesis approach is validated by the design and fabrication of a 30 W gallium nitride (GaN)-based class-AB power amplifier (PA) for GSM and WCDMA at 1800 MHz and 2140 MHz. The PA's output matching network based on the proposed structure can accurately match 50 Ω to the ideal load impedances of the transistor at two designed frequency simultaneously and has 20% and 15% bandwidth for which the reflection coefficient magnitudes are less than 0.1, respectively.

Volumetric left-handed metamaterials made up of an array of split-ring resonators (SRRs) and wires exhibit negative index of refraction in a very narrow bandwidth due to the resonant nature of SRRs. We investigate the possible bandwidth enhancement by adding resonances to the system using fractals. The operating bandwidth of the system is increased when the additional resonances are placed close enough to each other. The Sierpiński-carpet fractal pattern is chosen as the distribution for the SRRs. The principle is demonstrated through simulations, and prototypes are fabricated and tested to verify consistency with simulations.

The paper presents the description of multiply connected conducting regions (MCCR) in the finite elements space. In order to define induced currents distribution in multiply connected regions, an innovative method of combined vector potentials T and T₀ has been suggested. The equations of T-T₀ method have been presented. Moreover, the relations describing sources for the field of induced currents in the discussed regions have been given. The proposed method has been applied to solve Problem No. 7 of the International TEAM Workshops. The selected results of calculation have been compared with the measurement results.

Thermal non-destructive testing and evaluation of glass fibre reinforced plastic materials has gained more importance in aerospace industry due to low weight and high strength capabilities in severe environmental conditions. More recently, pulse compression favorable non-stationary excitation schemes have been exhibiting reliable defect detection capabilities in infrared non-destructive testing. This paper introduces a novel infrared non-destructive testing method based on quadratic frequency modulated thermal wave imaging with pulse compression for charactierization of glass fibre reinforced plastic materials. Defect detection capability of the proposed method has been experimentally validated using a glass fiber reinforced plastic (GFRP) sample with embedded Teflon inserts. Experimental results proved the enhanced depth resolution capability of the proposed excitation method as compared to the linear frequency modulation with pulse compression.

When a magnetic source is moved and/or oscillating above a conductive linear plate a traveling time varying magnetic field is created in the airgap. This field induces eddy currents in the plate that can simultaneously create normal and tangential forces. The transient fields and the forces created by the magnetic source are modeled using a novel 2-D analytic based A-Φ method in which the presence of the source field is incorporated into the boundary conditions of the plate. The analytic based solution is obtained by using the spatial Fourier transform and temporal Laplace transform. The performance of the method is compared with a 2-D transient finite element model with a Halbach rotor source field. The derived transient force equations are written in a general form so that they can be applied to any magnetic source.

In this paper, a novel circular ring patch antenna with tri-band operation is proposed for satisfying WLAN and WiMAX applications simultaneously. The proposed antenna consists of a circular ring patch, a straight strip and a door-shaped strip, all of which are printed on the top side of the substrate. The straight strip embedded in the rectangular slot is aimed to obtain resonant mode at 5.5GHz. With the use of a door-shaped strip symmetrically with the microstrip feed line, the proposed antenna can operate in three separate bands. The proposed antenna has been fabricated and tested. The numerical and experimental results exhibit the designed antenna operates over triple frequency ranges, and the 10 dB return loss bandwidths of the proposed antenna are 570 MHz (2.27-2.84 GHz), 470 MHz (3.35-3.82 GHz) and 1720 MHz (4.84-6.56 GHz), which can fulfill both the WLAN bands (2.4-2.484 GHz, 5.15-5.35 GHz, and 5.725-5.825 GHz) and the WiMAX bands (2.4-2.6 GHz, 3.4-3.6 GHz, and 5.25-5.85 GHz). In addition, a design evolution and a parametric study of the proposed antenna are presented to provide information for designing, modifying, and optimizing such an antenna. At last, the proposed antenna has an unusual advantage of omnidirectional radiation characteristics and stable gain over the whole operating bands.

Present study shows the development of integrated rain drop size distribution (DSD) model and gives a comparative study with DSDs of different regions in India. This work is useful for estimation of rain induced attenuation. Rain data of five different regions (Ahmedabad, Shillong, Thiruvananthapuram, Kharagpur and Hasan) was used for this work. Attenuation characteristics are different for different regions because DSD varies according to the climatic conditions. Development of DSD model for each location is not feasible. It is a demand to develop a integrated DSD model which gives the tolerable error in DSD for different regions, so that, it can be adjusted in fade margin of the communication system. The result of this work shows the good correlation between the proposed integrated DSD model and DSDs of different regions.

Coherent Change Detection (CCD) using multi-temporal Synthetic Aperture Radar (SAR) is one of the most important applications of remote sensing technology. With the advent of high-resolution SAR images, CCD has received a lot of attention. In CCD, the interferometric coherence between two SAR images is evaluated and analyzed to detect surface changes. Unfortunately, the sample coherence estimator is biased, especially for low-coherence values. The consequence of this bias is the apparition of highly coherent pixels inside the changed area. Within this context, the detection performance will considerably degrade, particularly when using high resolution SAR data. In this paper, we propose a new CCD method based on cleaning of coherence inside changed areas, which is characterized by high Local Fringe Frequencies (LFF) values, followed by a space-averaged coherence method. According to the proposed method, the results obtained with Cosmo-SkyMed (CSK) SAR data show an enhancement of change detection performance of about 6% while preserving subtle changes.

To improve the reflection performance of absorbers used in anechoic chambers, several different electromagnetic wave absorber geometries similar to conventional wedge absorber structures are proposed in this study. Design basics are examined by using the reflection and absorption of electromagnetic waves. The return loss characteristics of each absorber structure which is illuminated by a TE polarized plane wave have been obtained using well-known simulation software for several incidence angles. Comparisons of the simulation results of the conventional wedge and proposed absorbers are presented. The results show that new absorber shapes provide better absorption characteristics than a conventional wedge across almost all frequency ranges, and especially for normal and near normal incidence cases.

The paper presents an analytical investigation of three-layer twisted clad liquid crystal fiber in respect of its power propagation characteristics. The fiber under consideration has dielectric non-magnetic materials in its core and inner clad sections, whereas the outermost clad is made of radially anisotropic liquid crystal material. Twist in the fiber is introduced in the form of superfine helical turns at the interface of the core and the inner clad regions with specified values of pitch angle. Results demonstrate large confinement of optical power in the outermost liquid crystal section. Further, the angle of twist is seen to have its pronounced effect on controlling the flow of power as it exhibits the ability of governing the propagation characteristics of the medium. The observed propagation feature is attributed to the radial anisotropy of the liquid crystal outer region as well as the amount of twist introduced, and attracts useful applications of such complex fiber structures in evanescent field optical sensing and other coupling devices primarily used in integrated optics.

In this work, complex photonic band structure (CPBS) in a semiconductor-dielectric photonic crystal (SDPC) operating at terahertz frequencies are theoretically investigated. The SDPC is air/(S/D)^N/air where the dielectric layer D is SiO₂, the semiconductor layer S is an intrinsic semiconductor InSb, and N is the number of periods. Using the experimental data for the strongly temperature-dependent plasma frequency and damping frequency for InSb, we calculate the CPBS for the infinite SDPC at distinct operating temperatures. The CPBS is then compared with the calculated transmittance, reflectance, and absorptance as well in the finite SDPC. Based on the calculated CPBS, the role played by the loss factor (damping frequency), in InSb is revealed. Additionally, from the calculated transmittance spectra, we further investigate the cutoff frequency for the SDPC. The dependences of cutoff frequency on the number of periods and the filling factor of semiconductor layer are numerically illustrated.

The paper presents the design of a novel ultra-wideband microwave crossover for the use in microstrip circuits. The proposed structure includes a double microstrip-coplanar waveguide (CPW) vertical interconnect in single-layer substrate technology which allows an inclusion of a finite-width coplanar waveguide (CPW) on the top side of the substrate to achieve the required cross-link. The presented design is verified using the full-wave electromagnetic simulator Ansoft HFSS v.13 and experimental tests. The obtained experimental results show that in the frequency band of 3.2-11 GHz, the crossover has an isolation of 20 dB accompanied by insertion losses of no more than 1.5 dB.

We have synthesis ferrite-polymer nanocomposite structures, theoretically and experimentally investigated electromagnetic propagation, absorption properties of these nanocomposite materials at 8-20 GHz in microwave guides. The microwave properties of the samples were investigated by transmission line method, and reflection loss of -59.60 dB was found at 12 GHz for an absorber thickness of 2 mm. These nanocomposites may be attractive candidates for microwave absorption materials.

We propose an optofluidic based on two-dimensional (2D) rod-type silicon photonic crystal (PhC) waveguide that supports self-collimation effect over a large frequency and angle range without any defect or nano-scale variation in the PhC geometry. By analyzing the equi-frequency counter (EFC) of a triangular rod PhC-bands, we verify the optimum band of the structure which is suitable for self-collimation of light beams. By varying the refractive index of fluid being infiltrated into the background of PhC, we perform a systematic study of optofluidic self-collimation of light beams to achieve a wide range of angles and low loss of light. By means of selective microfluidic infiltration and remarkable dispersion properties, we show that it is possible to design auto-collimatator and negative refraction devices based on self-collimation effect with high transmission. We use the plane wave method (PWM) for analyzing the EFC and the finite difference time domain (FDTD) method for simulating the transmission properties.

This paper brings forward a simple local approximation finite-difference time-domain (FDTD) method for the analysis of short apertures with a finite thickness. By applying the equivalence principle together with a simple local approximation, the varying field distribution is accurately derived. The updating equations for the slot field can be derived by casting the field distributions into the contour paths containing the aperture. The method has been applied to two problems and the results are compared with the high-resolution standard FDTD simulation and the measurement results. The accuracy of the proposed method is verified from the comparison of both the field distribution and the time-domain and frequency-domain slot coupling results. It is demonstrated that the local approximation is highly efficient and timesaving, and the present method is stable, numerically and computationally efficient.

In this paper, an antenna-mode-switch technique is proposed to reduce the array size for the DOA (direction-of-arrival) estimation. Conventional DOA estimation requires many elements of antenna array to achieve high resolution, and then suffers from large array size. To improve such disadvantages, this paper proposes an antenna-mode-switch technique to reduce the required number of array elements. Numerical simulation shows that the required number of array elements will be greatly reduced by using the proposed technique. Furthermore, the bow-tie antenna design for implementing the proposed antenna-mode-switch technique is also given. The result proves that high-resolution and accurate properties of such a practical antenna design is very close to those of the ideal antenna mode.