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.

A dual-polarized small base station antenna with a dielectric feeding structure is presented. The proposed antenna is composed of a micro-strip feed line board, eight metallic shorting plates, four dielectric feed substrates, four metallic radiators, a metallic cube, and a radome. A wide impedance bandwidth of 20% (2.45 to 3.0 GHz) is achieved. The proposed antenna has an isolation of greater than 50 dB over the operating bandwidth. Details of the proposed antenna design, and the simulated and measured results are presented and discussed.

Recently, a novel approach for PN code acquisition of direct sequence code division multiple-access (DS-CDMA) systems in Rayleigh fading multipath channel was proposed in [1]. The authors considered a combination of adaptive thresholding constant false alarm rate (CFAR) and smart antennas to increase the system capacity and consequently enhance the detection performance. This paper considers still the problem of PN code acquisition for DS-CDMA communication systems over Rayleigh fading channels under the presence of multipath and multiple-access interference (MAI) signals. We propose and analyze an adaptive array acquisition system, which integrates an adaptive thresholding technique based on ordered data variability (ODV) index constant false alarm rate (ODVCFAR) and digital beamforming where a low complexity least mean square (LMS) algorithm is used to calculate the optimal weighting coefficients. This approach is expected to mitigate interferences caused by the presence of multiple access interference and multipath. Unlike other approaches based on a fixed censoring point when the number of interferences is assumed known, ODV-CFAR processing does not require prior knowledge about the number of interferences. The simulation results show a robust performance of the proposed system in varying mobile communication channels.

In this paper, a numerical study of a new ultra wideband (UWB) dielectric resonator antenna (DRA) is presented. The proposed structure consists of two stacked dielectric resonators excited by rectangular patch and operated from 3 GHz to 11 GHz (an impedance bandwidth of 115%), covering the full UWB spectrum. The analysis is carried out using the Finite Difference Time Domain (FDTD) method and two commercial electromagnetic simulators. The numerical results are given and compared in terms of reflection coefficients, radiation pattern and gain. The computed FDTD results are in good agreement with those of simulations.

The design of a compact coplanar power divider with novel structure is presented by making a full use of the theories of microstrip-to-slotline transition. To obtain two in-phase signals over a wide frequency range, the two output branches are placed in the same layer. Moreover, a half-wavelength slotline is employed to expand the working frequency range. The presented compact power divider shows a low insertion and good return loss performance at input port. The simulated and measured results have shown a good agreement over the frequency range 2.2 GHz-11 GHz.

In this study, a quad-band folded slot antenna with a monopole feed line embedded in a conductive housing structure (the LCD bracket of a mobile phone) is proposed. The performance of the proposed antenna is evaluated through simulation and measurement, demonstrating that it can provide total radiation efficiencies of more than 40% in the EGSM900, DCS, PCS, and WCDMA1 bands. Over these four bands, the total radiated power (TRP) of a prototype mobile phone using the antenna is 28.5, 27.1, 27.5, and 21 dBm, respectively, while the total isotropic sensitivity (TIS) is 102.7, 104.3, 103.8, and 107.3 dBm, respectively; all of these values satisfy Cellular Telecommunication and Internet Association (CTIA) requirements for over-the-area-(OTA) testing standards. The radiation performance of the proposed antenna in the calling mode is tested and shown to be within satisfactory limits; similarly, the specific absorption rates (SARs) of the prototype mobile phone are also found to be within standard SAR limits.

In this research paper, we propose supervised and unsupervised change detection methodologies focused on the analysis of multitemporal Synthetic Aperture Radar (SAR) images. These approaches are based on three main steps: (1) a comparison of multitemporal image was carried out by normalized difference ratio (NDR) operator; (2) implementing a novel supervised or unsupervised thresholding and (3) generating the change map by coupling of thresholding along with a region growing algorithm. In the first step, the two filtered multitemporal images were used to generate NDR image that was subjected to analysis. In the second step, by assuming a Gaussian distribution in the nochange area, we identified the pixel range that fits the Gaussian distribution better than any other range iteratively to detect the no-change area that eventually separates the change areas. In the supervised method, several sample no-change pixels were selected and the mean (μ) and the standard deviation (σ) were obtained. Then, μ±3σ was applied to select the best threshold values. Finally, a traditional thresholding algorithm was modified and implemented with the coupling of the region growing algorithm to consider the spatial information to generate the change map. The Gaussian distribution was assumed because it better fits the conditional densities of the no-change class in the NDR image. The effectiveness of the proposed methods was verified with the simulated images and the real images associated to geographical locations. The results were compared with the manual trial and error procedure (MTEP) and traditional unsupervised expectation-maximization (EM) method. Both proposed methods gave similar results with MTEP and significant improvement in Kappa coefficient in comparison to the traditional EM method was found in both cities. The coupling of the modified thresholding with the region growing algorithm is very effective with all methods.

Ultra Wideband Radar imaging has shown promising results in the detection of small tumours within low to medium density human breasts. A wide range of beamforming algorithms has been presented in several recent studies with good tumour localization capabilities, but most of these suffer a deterioration in performance with an increase in breast tissue density. In this paper, a preprocessing filter is used to compensate for path-dependent attenuation and phase effects, in conjunction with a range of existing data-dependent and data-independent confocal microwave imaging algorithms. Results indicate that this data preprocessing improves the performance of all beamformers, enabling detection and accurate localization of multiple tumours in mild to moderately dense human breasts. The proposed framework is tested on 3D anatomically accurate numerical breast models and the performance is evaluated across a range of appropriate metrics.

Numerical computation of induced surface current density, power gain, conversion efficiency, optimum interaction length and harmonic generation etc. pertaining to large-signal operation of a linear beam travelling wave tube amplifier (TWTA) employing a dielectric-loaded sheath helix model for the slow-wave structure based on the large-signal theory developed in Part 1 of this paper is presented, and comparison with the results of other large-signal theories and available experimental evidence is made.

In this paper, the design, realization, and experimental validation of a battery-assisted radio frequency identification (RFID) tag featuring sensing and computation capabilities are presented. The sensor-augmented RFID tag comprises an ultra-low-power microcon-troller, temperature sensors, 3-axis accelerometer, non-volatile storage, and a new-generation I2C-RFID chip for communication with standard UHF EPCglobal Class-1 Generation-2 readers. A preliminary printed-circuit-board prototype, connected to a 3-V/225-mAh lithium battery, provides a lifetime up to approximately 3 years when sensing and RFID-based communication tasks are performed every 10 seconds. Moreover, the device exhibits indoor transmission ranges up to 22 m, 6 m, and 5 m when attached to foam, concrete, and wood respectively. The encouraging results achieved for an emulated application scenario demonstrate the suitability of the device to be adopted in contexts where temperature and acceleration sensing are required.

Ground control point (GCP) extraction is an essential step in automatic registration of remote sensing images. However the lack of quantitative and objective methods for analyzing GCP quality becomes the bottleneck that prevents the broad development of automatic image registration. Although several measurements for evaluating the number, accuracy and distribution of GCPs have been proposed in recent years, some of them are redundant and the evaluation of dispersion is not effective enough. In this paper, a method for an objective and quantitative evaluation of GCP quality is proposed. The proposed method consists of three parts: measurement calculation, cost function calculation and final validation. In the first part, two new measurements are proposed to evaluate the number, dispersion and isotropy of GCPs, and the root mean square of GCP residuals using leave-one-out method (RMSloo) is used to evaluate the accuracy. In the second part, seed cost functions are utilized to transform the measurements into a limited value range as well as to be desired on the ascending direction. Subsequently, all the seed cost functions are combined by a total cost function to provide an integrated evaluation. In the third part, the GCP scenario is validated by the accepted threshold depending on the value of the total cost function. To evaluate the performance of the proposed method, experiments using four typical emulated scenarios of GCP distribution and two sets of real GCPs in SAR images are considered. The results demonstrate that the proposed GCP evaluation method performs more effectively than the existing methods, especially in the evaluation of dispersion quality.

A double-layered Vivaldi antenna enclosed by a metallic cylindrical cavity is investigated. The antenna is correlated to the same-size circular horn antenna to exploit the equivalent modal distribution of the Vivaldi-cavity antenna. It is shown that the TM₁₁ and TE₁₁ are the dominant modes and the proposed antenna operates similar to a dual-mode conical horn. The antenna is fabricated and successfully tested. The radiation characteristics, mutual coupling, as well as cross-polarization level are compared to a similarly sized Vivaldi without any metallic enclosure.

A rigorous field-theoretic method of analyzing the large-signal behavior of a linear beam traveling wave tube amplifier (TWTA) with slow-wave structure modeled to be a dielectric-loaded sheath helix is presented. The key step in the analysis is a representation of the field components as nonlinear functionals of the electron arrival time through a Green's function sequence for the slow-wave circuit. Substitution of this functional representation for the axial electric field component into the electron ballistic equation casts the latter into a fixed point format for a nonlinear operator in an appropriate function space. The fixed point, and therefore the solution for the electron-arrival time and hence the solution for the electromagnetic field components, can be obtained by standard successive approximation techniques. The calculations of the gain, the efficiency and the other amplifier parameters, comparison of the results of the present theory with experimental results etc., on the basis of such a successive approximation solution for the field components, will be presented in the second part of this paper.

This paper presents an analytical method to calculate the scattering parameters of a wireless power transmission link composed of electrically small single loop resonators. The proposed method takes into account all the different couplings in the structure. First, the method is presented and used to find the S-parameters for links composed of circular and rectangular resonators. The model is then used to find the optimal topology for a given transmission distance. Validation of the model is done by comparing its results with experimental measurements. Based on this model, a software used for the design of wireless power transmission links has been developed and is presented. Finally, demonstrations that this model produces excellent results are provided. At resonant frequency, an accuracy better than 2% is reached.

In this letter, a novel dual-band metamaterial absorber is presented and analyzed. The absorber is composed of four patches on the top of a thin grounded dielectric substrate which can absorb incident wave at two different frequency bands effectively. Then the absorber is loaded on the dual-band microstrip antenna, whose working frequency bands are overlapped with that of the absorber, to reduce the in-band RCS (Radar Cross Section) of antenna. The prototype is simulated, manufactured and measured. Simulated results show that the absorption of the absorber is as high as 98.6% at 4.29 GHz and 99.8% at 6.49 GHz. As to the dual-band antenna loaded with the proposed absorber, its radiation performance is unchanged while the RCS has declined by 8.59 dB at 4.29 GHz and 9.9 dB at 6.49 GHz respectively. There is a good agreement between simulated and measured results, which verifies that this absorber can be used for in-band RCS reduction of dual-band antenna so as to improve its in-band stealth performance.

We calculated analytic expressions for the absorption coefficient (ACF) of a weak electromagnetic wave (EMW) by confined electrons in cylindrical quantum wires (CQW) in the presence of laser radiation by using the quantum kinetic equation for electrons in the case of electron-optical phonon scattering. The ACF of a weak EMW depends on the intensity E₀₁ and frequency Ω₁ of the external laser radiation (E₁ = E₀₁sin(Ω₁t+φ₁)); the intensity E₀₂ and frequency Ω₂ of the weak EMW (E₂ = E₀₂sin(Ω₂t)), the temperature T of the system and the radius R of CQW. Then, the analytic results are numerically calculated and discussed for GaAs/AlAs CQW. The numerical results show that the ACF of a weak EMW in a CQW can have negative values. So, in the presence of laser radiation, under proper conditions, the weak EMW is increased. This is different from the similar problem in bulk semiconductors and from the case of the absence of laser radiation.

Excitation of waves at harmonics of electron cyclotron frequency due to utilization of an external alternating electric field is under the consideration. It is proved that they are eigen modes of plasma-dielectric-metal structures in both long (as compared with electron Larmor radius) wavelength range and short wavelength range if an external steady magnetic field is oriented perpendicularly to the plasma interface. It is assumed that uniform external electric field operates at the frequency, which belongs to the range of electron cyclotron frequencies. The problem is solved theoretically using kinetic Vlasov-Boltzmann equation for description of the plasma particles motion and Maxwell equations for description of TM polarized field of these modes. Non-linear boundary condition for tangential magnetic field of these TM-modes is formulated using conception of non-linear surface electric current. Infinite set of equations for harmonics of their tangential electric field is derived due to this condition. This set is solved using approach of the wave packet consisting of the basic harmonic and two nearest satellite harmonics. Simple analytical expression for growth rate of surface electron cyclotron TM-modes' parametric instability is obtained and analyzed numerically.

Investigation on dielectric frequency selective structure with arbitrary shaped grating is done numerically for filter applications. To obtain well designed parameters, the effects of shape, size and dielectric constant of the structure are carefully studied. We examine in detail various structures and their spectral response which have not been reported by other authors. It is also shown how the frequency selective behavior of the structure can be controlled to meet a specific purpose for narrow linewidth filtering for normal incident angle. Results obtained for the scattering of several dielectric frequency selective surfaces are compared with both theoretical and experimental results presented in the literature, showing very good agreement. The effect of arbitrary angle of incidence is also shown to excite higher-order Floquet modes that affect the filtering properties.

Since the characters of poor inherent resolution and low signal-to-noise limit the application of the passive millimeter wave (PMMW) image, it is particularly important to improve the resolution and denoise the PMMW image. In this paper, the adaptive manifolds filtering algorithm based on non-local means (AM-NLM) is illustrated in detail. And an improved version of AM-NLM filtering algorithm is proposed for processing the PMMW image. The proposed algorithm firstly applies the AM-NLM filtering to obtain the basic denoised PMMW image. Then the image enhancement based on Laplacian of Gaussian operator is performed to enhance the edge of the target in PMMW image. Finally, the hard-threshold filtering with different thresholds is adopted to filter each dimension to achieve the final filtering response. Experimental results have shown that the proposed PMMW filtering algorithm has better and more satisfactory performance compared to AM-NLM, both in subjective visual effect and objective image quality metric. Additionally, our proposed algorithm is also available for real PMMW images.

A mathematical model for accurately computing, when combined with the Fast Fourier Transform (FFT), the lightning currents flowing along a high voltage a.c. substation's grounding system buried in half infinite homogenous earth has been developedn in this paper. It is a hybrid of Galerkin's method of moment and the conventional nodal analysis method. The model can calculate the distribution of both branch and leakage currents along the grounding system. The dynamic state complex image method and the closed form of Green's function of a dipole or monopole in the half infinite homogenous earth model are introduced into this model to accelerate the calculation of the mutual impedance and induction coefficients. Analytical formulae for the mutual induction and impedance coefficients have been developed to accelerate the calculation for near field case by Maclaurin expansion. With the inverse FFT, the model can be used to study the transient lightning response of a grounding system.