This paper presents a novel conformal end-fire antenna whose design employs the Competitive Algorithm of Simulating Natural Tree Growth. This algorithm is based on the idea of simulating the processes of growth and wilting of natural trees and can search from simple to complicated structures with rapid convergence. Four optimized radiation elements were designed on a cross structure to verify the performance of the algorithm. A prototype of the designed antenna was also fabricated and tested. The antenna resonates at the center frequency of 2.45 GHz, exhibiting an ideal end-fire property. In addition, the measured and simulated results are in good agreement. Finally, we propose a novel end-fire antenna array based on the cross structure, with a radiation gain reaching 17.6 dBi.

This paper proposes a newly designed compact coplanar-waveguide-fed wideband circularly polarized (CP) printed square slot antenna (PSSA), in the square slot of which are a halberd-shaped feeding signal line and a square ring patch. By placing a specially designed metal reflector behind the bidirectional CP PSSA, one can obtain unidirectional CP patterns with a associated 3-dB axial-ratio bandwidth (ARBW) almost the same as that of the bidirectional antenna. The bidirectional L- and S-band PSSAs designed on FR4 substrates have 3-dB ARBWs as large as 25.3% and 29.1%, respectively. For the L-band antennas, the unidirectional design yields a 3-dB ARBW of 25.7% and a gain of about 3 dB higher than that of the bidirectional counterpart. In all these 3-dB axial-ratio bands, impedance matching with VSWR ≤ 2 is also achieved. Most importantly, the design concepts, procedures, and rules for the proposed antenna are presented in detail.

Based on linear optical transformation method, a diamond shaped reciprocal cloak with perfect invisibility in a certain direction is proposed. Compared with traditional cloaks, the object hidden inside the reciprocal cloak is not blind and can receive information from the outer region. Moreover, the reciprocal cloak is constructed of nonsingular homogeneous material parameters with reduced anisotropy that is relatively easy for practical realization. Full wave simulations validate the performance of the cloak.

A compact wideband dual-frequency microstrip antenna is proposed in this paper. By employing an offset microstrip-fed line and a strip close to the radiating edges in the circular slot patch, an antenna operating at dual frequency with the impedance bandwidth of 26.2% and 22.2% respectively is presented. By attaching a strip to the radiating edges opposite to the microstrip-fed line, this alters the current distribution and radiation on the antenna at the second resonant frequency. The second frequency is also tunable by varying the lengths of the microstrip-fed line. It is demonstrated that the proposed antenna covers the widebands of UHF and microwave for RFID application. A good agreement is obtained between the simulated and experimental results.

Design, simulation, and implementation of low profile microstrip spiral inductors for high power Industrial, Scientific and Medical (ISM) applications at the high frequency (HF-3-30 MHz) range are given for the first time. An accurate analytical model and algorithm have been developed to determine the simplified lumped element equivalent model parameters for spiral inductor and its physical dimensions. Five different spiral inductors are then simulated with a planar electromagnetic simulator using the physical dimensions obtained for the desired inductance values with the analytical method. The implementation method and substrate selection for spiral inductors at the HF range are given in detail for high power applications. The spiral inductors are then constructed on 100 mil Alumina substrate and measured with network analyzer. It is found that analytical, simulation and measurement results are in close agreement and the analytical method and algorithm that have been developed can be used to accurately determine the physical dimensions, and the resonant frequency of the spiral inductor for the desired inductance value.

This paper introduces a novel design of Butler matrix in substrate integrated waveguide (SIW) technology with wide frequency band characteristics. Butler matrices are particularly useful in advanced antenna design and characteristics such as wideband operation, power handling, manufacturing, integration, cost, etc. are typical issues to be addressed in many applications. The proposed planar 4×4 Butler matrix provides an interesting solution to most of these issues. Wideband operation is achieved thanks to improved cross-couplers. These components are also characterized by higher power handling when compared to $E$-plane couplers. The use of SIW technology enables to reduce insertion losses compared to other printed technologies, while maintaining most advantages of such technologies such as high integration, manufacturing simplicity, low weight, etc. The proposed design is fully described, from the elementary building blocks to the full assembly performances. The design is optimized for operation in Ku-band with a center frequency at 12.5 GHz. A prototype of the 4×4 Butler matrix is manufactured, and good performances are confirmed over 24% relative frequency bandwidth. Potential use of this sub-system in multibeam antenna design is also discussed.

There is increasing interest in electromagnetic interference (EMI) shielding due to the serious electromagnetic environment pollution caused by the continuously increased use of the electrical products and electronic devices. Electrical conductivity and EMI shielding effectiveness (SE) of composite materials made from silicone rubber with carbon powder and ferrite powder have been studied in microwaves and terahertz frequency ranges and the results are presented in this paper. In microwaves range, samples with higher electrical conductivity show a small variation of shielding performance with frequency, whereas the performance of samples with lower conductivity falls away with increasing frequency. It is shown that the variation of attenuation with frequency relates to the conductivity of the material.

Because of the asymmetry of six-port junctions and the nonlinearity of diode detectors, the calibration of direction finding receivers have to be carefully considered. It is generally believed that an efficient tool for numerical approximations, the artificial neural network (ANN), may be used for such calibrations. In this paper, a new calibration technique based on the ANN is proposed for direction finding receivers at a bandwidth of 1 GHz. The direction finding system adopts a zero-intermediate frequency receiver architecture, which offers the advantage of fast response times. The key modules of this receiver consist of two six-port networks used to measure phase differences and operating frequencies. The results indicate that the calibration technique achieves a high accuracy of 0.192°.

This paper presents the design of a broadband circular polarization truncated horn antenna with single feed. It does not require any complex feeding structure and uses only a coaxial feed extended with a simple electric field coupling probe. The corners of the horn are truncated to generate circular polarization modes, and a broad axial ratio bandwidth which is insensitive to the probe feed dimension is achieved. Simulated and measured results of an S band truncated horn antenna are presented. The antenna has a broad 3 dB axial ratio bandwidth of 26% with aperture efficiency of 60%.

Whole-body averaged specific absorption rate (WBA-SAR) is used as a metric for human protection from whole-body exposures. The frequency at which the WBA-SAR becomes maximal is called ``resonance frequency''. The present study proposes a scheme to estimate WBA-SAR at the resonance frequency based on an analogy between a human and a quarter-wavelength monopole antenna. Specifically, WBA-SAR can be estimated with the human body resistance once ankle current was obtained. Thus, it is essential to investigate the effective resistance for anatomically-based human models. Then, the effective resistances for different humans grounded on the perfect conductor are calculated to clarify the variability. The main factors for the variability were attributed to the body shape and model anatomy. In particular, WBA-SARs in human models grounded are found to be estimated from their BMI and respective measured ankle current in realistic environment, including a scenario of multiple wave exposure.

Microwave radar and microwave-induced thermoacoustic technique exploit the contrast in the permittivity and conductivity between malignant and healthy tissue. They have emerged as promising techniques for detecting breast cancers. This paper compares the imaging capability of these techniques in the presence of homogeneous and heterogeneous breast tissue. Relying on the data from the finite-difference time-domain simulations, the study shows that both techniques are capable of imaging homogeneous objects. In the presence of electromagnetic dispersion and heterogeneity, radar signals suffer from strong dispersion and multiple scattering, which decorrelate the signals with the scatterers. The microwave-induced thermoacoustic technique takes the advantage of breast being acoustically homogeneous and is capable of generating high-quality images.

In this paper, a new radar constant false alarm rate detector to perform adaptive threshold target detection in presence of interfering targets is proposed. The proposed CFAR detector, referred to as Adaptive Linear Combined CFAR, ALC-CFAR, employs an adaptive composite approach based on the well-known cell averaging CFAR, CA-CFAR, and the ordered statistics, OS-CFAR, detectors. Data in the reference window is used to compute an adaptive weighting factor employed in the fusion scheme. Based on this factor, the ALC-CFAR tailors the background estimation algorithm. The conducted Monte Carlo simulation results demonstrate that the proposed detector provides low loss CFAR performance in an homogeneous environment and also performs robustly in presence of interfering targets. The performances of the ALC-CFAR detector have been evaluated and compared with that of the CA-CFAR and the OS-CFAR detectors. The obtained results are presented and discussed in this paper.

A study of the raindrop size distribution along the eastern coast of South Africa (Durban) is presented. The Biweight kernel estimator based on distometer measurement is used to determine the best estimate of the measured raindrop size probability distribution function (pdf). The best kernel estimator, which results in the lowest integral square error (ISE), is used to measure the closeness of the estimated lognormal and gamma pdf of raindrop size to the measured raindrop size distribution. It is established that the optimised lognormal pdf slightly outperforms the optimised gamma pdf in terms of the mean ISE and the RMSE values, with mean ISE values of 0.026 for lognormal and 0.04 for gamma distributions, respectively, and corresponding mean RMSE values of 0.073 and 0.081, respectively. The method-of-moments gamma and lognormal distributions are observed to be worse estimators of the measured pdf than the two optimized distributions. The N(D) distributions using the optimised l gnormal and gamma distributions for the region are compared with those for different tropical regions, namely, India, Singapore, Nigeria, Indonesia, and Brazil. While the Indian lognormal N(D) model gives the highest peak for low raindrop sizes for all rain rates, Durban's gamma and lognormal models exhibit the widest raindrop size spread over all rain rates ranging from 1-120 mm/h. Finally, the specific attenuation due to rain using the Durban models are compared against the ITU-R models and actual measurements over a 19.5 GHz LOS link; the results indicate a need for further work involving both distrometer and radio link measurements for rain rates exceeding 30 mm/h in the eastern coast of South Africa.

This paper presents a new quadrature voltage-controlled oscillator (QVCO), which consists of two p-core Colpitts cross-coupled voltage-controlled oscillators (VCOs) with an LC ring resonator to provide the quadrature outputs. The proposed CMOS QVCO has been implemented with the TSMC 0.18 μm CMOS technology and the die area is 0.478 x 0.82 mm². At the supply voltage of 1.5 V, the total power consumption is 20.4 mW. The free-running frequency of the QVCO is tunable from 9.69 GHz to 10.52 GHz as the tuning voltage is varied from 0.0 V to 2 V. The measured phase noise at 1 MHz frequency offset is -122.41 dBc/Hz at the oscillation frequency of 10.52 GHz and the figure of merit (FOM) of the proposed QVCO is -189.7 dBc/Hz.

In this study, refractive index changes associated with intersubband transitions in a spherical quantum dot, GaAs/Al_xGa_1-xAs, have been theoretically calculated in the presence of impurity. In this regard, the effect of dot radius, stoichiometric ratio, impurity and incident optical intensity on the refractive index changes have been investigated for the transitions between higher energy states, i.e., 1s-1p, 1p-1d and 1d-1f. The results show that these parameters have a great influence on the refractive index changes.

In this paper, we propose a simplified particle probability hypothesis density (PHD) filter and its hardware implementation for multiple-target tracking (MTT). In the proposed algorithm, the update step of particle PHD filter is simplified and the time-varying number of measurements is arranged in combination series/parallel mode. This may result in fixed hardware architecture and therefore present a convenient hardware implementation of particle PHD filter. Simulation results indicate that for the MTT problems, this proposed simplified algorithm shows similar performance with the standard particle PHD filter but has faster processing rate. Experiment study shows that the proposed simplified algorithm can be efficiently implemented in hardware and can effectively solve the MTT problems.

In the final step of any filter design process, the desired center frequency, coupling factor and external quality factor (Q_ext) are used to determine the physical parameters of the filter. Although in the most cases the physical dimensions of a single resonator for a given center frequency are determined using exact analytical or simple approximate equations, usually such simple equations cannot be found to easily relate the required coupling factor and Q_ext to the physical parameters of the filter. Analytical calculation of coupling factor and Q_ext versus dimensions are usually complicated due to the geometrical complexities or in some cases such as microstrip resonators due to the lack of exact solution for the field distribution. Therefore coupling factor and Q_ext of various kinds of resonators, especially microstrip resonators, are related to the physical parameters of the structure by the use of time consuming full wave simulations. In this paper a surprisingly fast and completely general approach based on a soft computing pattern-based processing technique, called active learning method (ALM) is proposed to overcome the time consuming process of coupling factor and Q_ext determination. At first the ALM technique and the steps of modeling are generally described, then as an example and in order to show the ability of the method this modeling approach is implemented to model the coupling factor and Q_ext surfaces of microstrip open-loop resonators versus physical parameters of the structure. Using the ALM-based extracted surfaces for coupling factor and Q_ext, two four pole Chebychev bandpass filters are designed and fabricated. Good agreement between the measured and simulated results validates the accuracy of the proposed approach.

A convergence study of a non-standard Schwarz domain decomposition method for finite element mesh truncation in electromagnetics is carried out. The original infinite domain is divided into two overlapping domains. The interior finite domain is modeled by finite elements and the exterior infinite domain by an integral equation representation of the field. A numerical study of the spectrum of the iteration matrix for non-convex mesh truncation boundaries is performed. The projection of the error between two consecutive iterations onto the eigenvector space of the iteration matrix is performed. The numerical results explain the observed convergence behavior of the Schwarz iterations.

A numerically efficient approach for the rigorous computation of bi-static scattering and radiation problems is presented. The approach is based on an improvement of a previous method scheme that combines the Characteristic Basis Function Method (CBFM) and the Multilevel Fast Multipole Algorithm (MLFMA). The approach combines Characteristic Basis Functions (CBFS) and subdomains functions for reducing the CPU time in the pre-process and in the solving iterative process for simple or multiple excitations. It is intended for use in very large cases where an iterative solution process cannot be avoided, even considering the matrix size reduction achieved by the CBFM. This reduction is particularly important for solving radiation or bistatic problems in which an integral equation is solved once.

This paper deals with an investigation on the polarization of an antenna array with a circular geometry. The theory shows that the polarization of a circular array exhibits a circular polarization independent of the antenna elements. Circular polarization is then achieved whatever the polarization of the elements of the array. Moreover, due to the circular geometry of the array, the entire far field pattern of the array can be obtained with the measurement or the simulation of only one antenna inside the array. The influence of the array radius on the polarization performances has been investigated. An antenna array has been built, and measurements have been performed in order to corroborate the theoretical results.