In this paper, a printed wideband Yagi-Uda antenna with a novel folded dipole driver is proposed. The folded dipole driver is comprised of a folded dipole and a microstrip feedline which functions as an internal balun to mainly determine its wide impedance bandwidth. With the optimized parameters, an operating band of 1.69 GHz~2.72 GHz can be obtained. Besides the folded dipole driver, the broadband printed Yagi-Uda antenna also consists of three directors and a reflector. Its wideband performance is mainly determined by the folded dipole driver, while the reflector and directors improve its performance slightly. By optimizing the geometrical parameters of the folded dipole driver, a bandwidth of 61.8% (1.53 GHz~2.93 GHz) for return loss being higher than 10 dB is achieved. The proposed printed Yagi-Uda antenna is realized on FR4 substrate with a measured operating bandwidth of 62% (1.51 GHz~2.94 GHz), a flat gain (5.6 dB~7.3 dB), more than 10dB front-to-back ratio and lower than -15 dB cross-polarization level.

A goal of this work is to find a possible explanation of the experimental results of [1] where the wireless power transfer between two coils is investigated. We show that this wireless power transfer is provided by the longitudinal component of the EM field. Using Jefimenko's approach of solving the Maxwell equations we show that under specific conditions the longitudinal component drops with the distance as 1/R. This result dependence can explain the experimentally detected dependence of the transferred power in the experiment.

The range profile (RP) and the inverse synthetic aperture radar (ISAR) image are the useful radar signature for classifying unknown targets because they can be used regardless of day-night and weather conditions. Since classification that uses RP and ISAR is heavily dependent on flight conditions, however, much more study is required on this topic. This paper proposes an efficient method of classifying targets by using a classifier-level fusion of RP and ISAR as well as a scenario-based construction method of the training database. Simulation results using the five targets composed of point scatterers prove that the proposed method yields high classification results when the targets are flying in a variety of directions at both short and long ranges.

In this paper, we propose a novel UHF RFID coupled slot metallic tag antenna with a radome. The proposed tag antenna consists of a frequency tuning slot, imaginary part tuning slot, real part tuning stub, micro-chip, and radome. All simulations were carried out using an Ansys HFSS simulator. The RFID tag antenna was designed and fabricated for use in the Korean and Japanese UHF band of 916.7 to 923.5 MHz. The measured 3 dB frequency bandwidth is 914 to 926 MHz. The measured read range is 12 m on a metallic surface. Details of the proposed tag antenna design, as well as simulated and measured results are presented and discussed.

Cuckoo optimization Algorithm (COA) is employed for the optimization of linear and non-uniform circular antenna arrays. COA is a novel nature inspired computing algorithm which is motivated by the life of Cuckoo. Like other nature-inspired algorithms, COA is also a population-based method and uses a population of solutions to proceed to the global solution. The method of COA is used to determine a set of parameters of antenna elements that provide the required radiation pattern. The effectiveness of COA for the design of antenna arrays is shown by means of numerical results. Comparison of results obtained with COA is made with that obtained using other popular methods. The results reveal the superior performance of COA as compared to other techniques both for design of linear and circular antenna arrays.

In this paper, the range-spread target detection in compound Gaussian clutter with reciprocal of the square root of gamma (RSRG) texture is investigated. The RSRG distribution has been proved to be a good model for texture component of extremely heterogeneous radar clutter. Taking this compound Gaussian model as a spherically invariant random process (SIRP), the Neyman-Pearson optimal detector for the range-spread target detection with known target amplitude is derived firstly. By replacing the ideal target amplitude with its maximum likelihood estimate (MLE), the generalized likelihood ratio test (GLRT) is then obtained. The statistical property of the texture component is taken into account in both of these two detectors, which makes the detectors computationally complicated. A suboptimal generalized likelihood ratio test based on order statistics (OS-GLRT) is finally proposed by substituting the texture component with its MLE. The OS-GLRT makes use of some largest observations from the range cells occupied by the most likely target scatters. The performance assessment conducted by Monte Carlo simulation validates the effectiveness of the proposed detectors.

A wideband circularly polarized patch antenna is proposed. The wide impedance and axial ratio bandwidths are achieved by the proposed feeding mechanism, which entails the use of a circular microstrip line coupling through four Γ-shaped slots to generate four sequentially phased sources to excite the single layer patch antenna. The proposed antenna can provide an SWR bandwidth of over 16.5% (for SWR<1.5) and an axial-ratio bandwidth of 13.3% (for AR<3 dB). The performance of the antenna has been confirmed by both measurement and simulation. The antenna gain is enhanced and backlobe radiation is reduced by placing a reflector at an optimized location.

An approach based on the use of the arithmetic of intervals and Interval Analysis for the solution of inverse scattering problems is presented and assessed. By exploiting the property of the Interval Analysis to find the global minimum of a functional in a n-dimensional space, the proposed approach adopts a branch and bound process to discard the regions of the solutions space not containing the global solution, while keeping those where a feasible solution is expected until a suitable converge criterion is reached. A representative set of results concerned with the reconstruction of circular dielectric objects within the first-order Born approximation are reported and discussed to show potentialities and current limitations of the proposed approach.

When the metal film is thicker than the skin depth in the working frequency band, the transmission characteristics of outer coated type are superior to the transmission properties of inner coated type under the same size. Further more, the transmission properties of the single, double, three and four groove both for inner coating and outer coating terahertz (THz) polystyrene (PS) tubes are studied in this paper. In result, the transmission properties of single and double slot are good, but the three and four slots' transmission characteristics deteriorate. In addition, slots width affects the transmission characteristics of PS tubes evidently, and the attenuation coefficient of outer coated PS tube with single slot is proportional to the slot width, so as to optimize the transmission properties of PS tube. It is a compromise for the slot width (it is better to choose appropriate slot width).

General expressions for the quality factor (Q) of antennas are minimized to obtain lower-bound formulas for the Q of electrically small, lossy or lossless, combined electric and magnetic dipole antennas confined to an arbitrarily shaped volume. The lower-bound formulas for Q are derived for the dipole antennas excited by both electric and magnetic surface currents as well as by electric surface currents alone. With either excitation, separate formulas are found for the dipole antennas containing only lossless or nondispersive-conductivity material and for the dipole antennas containing highly dispersiveconductivity material. The formulas involve the quasi-static electric and magnetic polarizabilities of the associated perfectly conducting volume of the antenna, the ratio of the powers radiated by the electric and magnetic dipoles, and the efficiency of the antenna.

Local Area Augmentation System (LAAS) is expected to enable the pilots to guide the aircraft more precisely and safely into busy airports even in poor visibility conditions. The anomalous low and equatorial latitude Ionosphere is severe threat to the LAAS system. To characterize the anomalous ionospheric gradients, the performance of an ionospheric threat model is evaluated. In our investigation, in contrast to the reported work available in the open literature, smoothed code phase measurements are used in the threat model to obtain precise ionospheric time delay. The three key parameters of the threat model gradient slope (mm/km), width (km) and front speed (m/s) are used in the analysis. Further, geometry screening using Maximum Ionosphere Induced Error in Vertical (MIEV) as a key parameter is carried out to identify the stationary gradients and its impact on system performance for CAT-I operations. A maximum ionospheric gradient of 355.74 mm/km over a distance of approximately 75 km is reported at mid latitudes. Whereas, in our findings at low/equatorial latitudes even within a distance of approximately 4 km a maximum gradient of 460 mm/km is observed, which is comparatively very high. Our results show that, there is necessity to enhance upper bound for the ionospheric gradients threat space over low latitudes.

In this paper, we introduce plane wave modulators that are designed using one-dimensional photonic crystals (1DPC) containing radial gradient refractive index (r-GRIN) defect layers. Three kinds of r-GRIN materials with different refractive index distribution functions are applied in numerical analysis. The properties of the phase and intensity of the transmitted plane wave beam through propoesed structures are studied using the transfer matrix method. Radially-dependent defect modes, modulated phase and intensity are obtained according to the refractive index distribution functions. The results are predictable by regarding the Bragg condition and destructive interference, which are the origins of the photonic band gap. Due to the radial-dependency of the defect layer's refractive index, the rays passing through different transverse positions experience different optical pathways. Therefore, the defect modes and transmitted spectrum (phase and amplitude) vary transversely. This study demonstrates another ability of the artificial PC structures to design plane wave modulators and manipulate its phase and intensity.

We propose a theoretical study on the electromagnetic wave scattering from layered structures with an arbitrary number of rough interfaces by using the small perturbation method and the small slope approximation. The interfaces are characterized by Gaussian height distributions with zero mean values and Gaussian correlation functions. They can be correlated or not. The electromagnetic field in each medium is represented by a Rayleigh expansion and a perturbation method is used for solving the boundary value problem and determining the first-order scattering amplitudes by recurrence relations. The scattering amplitude under the first-order small slope approximation are deduced from results derived from the first-order small perturbation method. Comparison between these two analytical models and a numerical method based on the combination of scattering matrices is presented.

Structural, vibrational and microwave dielectric properties of Nickel-Copper-Zinc ferrite (Ni_0.2Cu_xZn_0.8-xFe₂O₄) ceramics have been presented in this paper. Samples have been prepared using conventional auto-combustion method. The X-ray diffraction (XRD) results confirmed the ferrite samples to be of cubic spinel structure, which further was validated by Fourier transform infrared (FT-IR) and Raman spectroscopy. The relative permittivity (ε_r) increased from 7.474 to 8.132 with successive increase in Cu content. The observed and calculated permittivity using Clausius-Mossoitti relation have been in good agreement. The temperature coefficient of resonant frequency (τ_f) decreased from -75.85 ppm/°C to -32.12 ppm/°C with increase in successive Cu content. The relative permeability (μ_r) have been calculated by using the Nicholson-Ross-Weir conversion technique. Using Ni_0.2Cu_0.2Zn_0.6Fe₂O₄ sample the ferrite resonator antennas have been designed in three different shapes. The experimental and theoretical characteristics of the antennas have been compared and a good agreement has been achieved.

The human body has got a pivotal role in portable devices operating in Body-centric Wireless Networks (BCWNs). Electromagnetic interaction between lossy human body tissues and wearable antennas degrades the system performance. Efficient deployment of such systems necessitates thorough understanding of these effects. Numerical analysis is a powerful tool that provides useful information of such scenarios fairly quicker than the actual measurements giving the user full control of the design environment. This paper investigates usefulness of numerical analysis based on the comparison of three different homogeneous models of the human body. Effectiveness of a numerical model is evaluated in terms of its resolution, computational efficiency, time consumption and accuracy of the results in software followed by experimental verifications.

Radar features of wind turbines are simulated and studied in the HF band. The features are presented in the range-Doppler plane for single as well as arrays of turbines. Doppler aliasing due to the limited pulse repetition frequency of HF radars is examined. Shadowing characteristics of arrays of turbines are simulated and analyzed. Electromagnetic modeling details including effects of thin-wire modeling, non-conducting turbine components, and the presence of a conducting ground surface are discussed.

In this paper, a novel forward-looking imaging method based on the compressed sensing is proposed for scanning phased array radar (PAR) in order to improve the azimuth resolution,. Firstly, the echo of targets is modeled according to the principle of PAR. Then, it is analyzed why some of the former methods as multi-channel deconvolution are ineffective based on the signal model. Using a widely accepted assumption that dominant scatterers in an interesting area are sparse or compressible, an imaging algorithm based on the compressed sensing is proposed and investigated. This method obtains its high range resolution by transmitting and compressing chirp pulse signal, and improves its azimuth resolution by utilizing the compressed sensing technique. The effectiveness of the proposed method is illustrated and analyzed with simulations data.

This work presents a novel comparative modeling scheme for single-ended (SE) through-silicon vias (TSVs) in GSG and GS configurations. Physical scalable models based on the equations developed herein indicate that the use of two symmetric ground TSVs in GSG configuration relatively increases the parasitic capacitance and conductance in the silicon substrate. However, this increase in the parasitic capacitance requires that the parasitic inductance of SE TSV is reduced to maintain the same phase velocity in silicon. According to the modeling results, the GSG configuration has a larger insertion loss than that of the GS configuration because the former has a higher substrate conductance. Nevertheless, when measured using RF coaxial probes, the GSG configuration exhibits a larger measurement bandwidth than the GS configuration. Finally, with the assistance of a double-sided probing system, wideband S-parameter measurement can validate the established equivalent-circuit model of SE TSV in GSG configuration up to V-band frequencies.

The dispersion properties of an anisotropic metamaterial composed of periodic stacking of graphene-liquid crystal layers are investigated in the far-infrared region. It is represented that this structure is able to show both the elliptic and hyperbolic dispersions using the tunable properties of the graphene and liquid crystal. The switching between two dispersion phases via control of the temperature, voltage and external electric field is studied. It is shown that this switching can be used to control of the transmission and reflection at the interface of the metamaterial and air.

Integrating antennas into a load-bearing airframe structure has the potential for profound improvements in the capability of military and commercial airplanes, by allowing for substantially increased radiator and array size with reduced weight or drag penalties. Reducing the size of array elements can significantly improve the mechanical performance of the loadbearing antenna. The novel single element spiral slot cut in the broad-wall of a WR-90 rectangular waveguide proposed in this paper is smaller than a quarter of the operating wavelength (half of the size of a conventional rectangular slot). The small antenna element enables a slotted waveguide array to be realized without significantly degrading the mechanical performance in load bearing applications. The proposed spiral slot is compared with conventional rectangular slots and exhibits comparable performance in terms of total efficiency (representing coupling from waveguide mode to the slot) and peak realized gain. Total efficiency and peak realized gain of the spiral slot in travelling wave mode are significantly higher than those of a quarter wavelength rectangular slot element which has near zero radiation. The simulated results were validated by manufacturing the spiral slot placed on the broad-wall of a rectangular waveguide. Realized gain patterns of the spiral slot measured at the design frequency corroborate reasonably with the simulations.