A novel Competitive Algorithm of Simulating Natural Tree Growth is presented in this paper. It searches from a simple status to complex ones and is characterized by quick convergence. The algorithm has been used to design a novel tree-shaped antenna which has an appreciably larger gain of 2\,dBi more than traditional dipole antenna with a reflector of the same size. A prototype antenna has been fabricated and tested. A good agreement between the calculated and measured results verifies the feasibility of the algorithm.

An open-ended waveguide probe has been adapted for complex permittivity determination and hence mechanical property inspection of cement-based materials. The probe uses amplitude-only reflection measurements at different frequencies for this goal, which is suitable for industrial based applications when cost and ease of use are important considerations. We have derived expressions by taking into account of the wavematerial interaction. The reference plane for measurements is set inside the waveguide to measure solely the reflected signal of the dominant mode. It is shown that the measurement results are in good agreement with the theory.

In this paper, we study metamaterial-based transparent shells, which are invisible to electromagnetic waves and fields. More general topics, including material loss, material discretization and far field distribution etc. are covered in order to facilitate possible realization. We design and analyze the transparent shells using optical transformation. Unlike the widely-studied cloaking devices which make the objects inside invisible, the transparent shells physically cover and shield the devices inside without sacrifice of their electrical performance since they are transparent to incoming electromagnetic waves. Due to the simple constitutive parameters, these transparent structures could be realized using artificial metamaterials in a wide frequency band, which may have wide applications in civil and military areas.

In this paper, a method to broaden the beamwidths of a crossed dipole antenna is proposed. By introducing four parasitic strips around the crossed dipole antenna, the beamwidths of the crossed dipole antenna in the vertical plane are broadened effectively, making the patterns uniform over a wide frequency band. An L-band prototype, operating in the frequency range from 1.1 GHz to 1.6 GHz, is fabricated and tested. The simulated and measured results show that the beamwidths at lower frequencies are broadened and uniform radiation patterns over the whole operating frequency band are obtained, making the crossed dipole suitable for wideband marine GPS (Global Positioning System) applications.

A simple, closed-form expression for the time-domain reflection coefficient for a pulsed TE10-mode wave incident on a dielectric material discontinuity in a rectangular waveguide is presented. This formula may be used to represent the transient field reflected or transmitted by a dielectric-filled waveguide section, which is useful in material characterization routines. An exponential function approximation to the reflection coefficient is presented, and the formula is validated both numerically and experimentally.

A one dimensional tunable periodic structure in microstip technology on gallium arsenide (GaAs) substrate is numerically investigated. The unit cell contains a number of patches positioned between the ground plane and the microstrip line. The patches, representing reactive loads, can be selectively short-circuited by externally-ontrolled FET switches integrated in the hosting substrate. The possibility of controlling the position of the band-gap, and implicitly the value of the effective dielectric constant along the line, for different combinations of the switches is demonstrated.

This paper introduces two new type active quasi circulators and three new type active circulators which use the out-of-phase power divider/combiner, symmetric/anti-symmetric couplers and generic unilateral amplifiers. The proposed circuits are full-symmetric and composed of conventional microwave devices. Analytical relations for active quasi circulator modules are described. These modules have many variations and can be used for very wide frequency range depending on the type of the employed unilateral amplifier, power divider/combiner and symmetric/anti-symmetric couplers. Based on the proposed configurations, analysis and design of n-port active circulators are presented. Also they can be used in MMICs as active quasi circulators, active circulators and in other high frequency applications.

This paper analyzes the possibility to use dimension and lacunarity for comparing the resonant behavior of different convoluted wire antennas, including prefractal dipoles. Since previous studies have proved that the Hausdorff fractal dimension is not suitable for antenna comparison purposes, this work proposes the adoption of a different approach for evaluating the dimension by using the measurement at scale δ, which is more suitable for analyzing real phenomena. The results provided by this measure are compared to those obtained by using the average lacunarity. The objective is to verify if, given two convoluted wire dipoles, the dimension and average lacunarity provide sufficient information to infer which dipole exhibits the lower resonances.

In this paper, for developing analytical and semi-analytical methods to evaluate band structure in photonic quasicrystals the perturbation theory is examined. It is shown that more isotropic and complete photonic band gap can be observed under low dielectric contrast for photonic quasicrystals in comparison with ordinary crystals and because of this feature of photonic quasicrystals, perturbation theory is suitable for evaluation of these structures. In this work, we show that using perturbation semianalytical method one can obtain complete band structure for quasicrystals that are interesting for terahertz technology especially and microwave and optical engineering too. Also, we investigate that complete band gap is appeared in quasicrystals in low refractive index contrast and with increasing number of fold in quasicrystals gap size and isotropy are increased.

This study investigates the effect of incorporating Doppler velocity measurements into the most commonly used sequential track initiation schemes, the rule and logic based schemes. The measurement set has been expanded from range and azimuth to include elevation and Doppler velocity. Unlike previous studies, elevation and Doppler measurements have also been included in the analytical evaluation of the false track initiation probability. Performance improvement obtained by employing Doppler measurements has been demonstrated through simulations in terms of false track initiation probability and true track initiation probability. Receiver Operating Characteristics and System Operating Characteristics have also been utilized in performance evaluation. Analytical derivations and simulations have revealed that, using Doppler velocity measurements along with 3D position measurements while initiating tracks in clutter leads to significant decrease in false track initiation probability while providing an acceptable level of true track initiation probability. Simulation results have also showed that inclusion of Doppler measurements has reduced the required time for track initiation, resulting in faster track initiation.

In this work, the efficient analysis and design of optimised turnstile junctions showing low reflection coefficient is investigated. For this purpose, a rigorous multimodal analysis of compensated junctions is developed, which is based on the computationally efficient 3-D Boundary Integral-Resonant Mode Expansion (3-D BI-RME) technique. The electrical performance of the standard turnstile junction has been drastically improved by compensating this microwave component using piled-up partial-height cylindrical metallic posts placed on the base of the junction. Moreover, the authors demonstrate that improved designs can be derived by compensating the turnstile junction using one single cylindrical post, which is easier to manufacture than a piled-up post, and it is a more robust element to confront high-power effects. This novel Computer-Aided Design (CAD) tool has been verified through excellent comparisons between the obtained results and those provided by the technical literature, and also by a well-known commercial finite-element method software.

Quasi-optical (QO) techniques have been extensively studied in recent years because of the promise they hold for medium and high power generation at millimeter- and sub-millimeter-wave frequencies, demonstrating higher efficiency than conventional approaches. In this work a step-by-step flow process is proposed for the design of a slot-based QO amplifier. The proposed design procedure is based on full-wave analysis of the individual building blocks, which are then cascaded to represent the whole system. An experimental assessment is proposed based on the design and on experimental analysis of the behavior of a C-band QO unit cell.

In this paper, we have extended the recently introduced theory of coupled propagation of two coaxially co-propagating and mutually incoherent bright 1-D beams to coupled propagation of two 2-D (cylindrical) bright beams and investigated the propagation behavior and spatial soliton pair formation of such beams by a recently introduced simple approach. We have considered saturable form of the nonlinear medium in this paper as 2-D spatial solitons are unstable in Kerr type media. We found that many of the propagation features of two 2-D beams in saturable media are same that of 1-D beams in Kerr type media. However, many features are different and to the best of our knowledge, reported in this paper for the first time. The present version of the theory is applicable in all possible physical situations and parameters.

This paper reports the design and development of rectangular microstrip antenna comprising a novel slot for enhancing the impedance bandwidth and gain. By incorporating a slot of optimum geometry at suitable location on the radiating patch, the antenna provides 78.08% (3.39 - 7.73 GHz) of impedance bandwidth and 3dB of gain without changing the nature of broadside radiation characteristics when compared to conventional rectangular microstrip antenna. The proposed antenna may find applications in mobile WiMax, IEEE802.11a, HIPERLAN/2, cordless phones, fixed wireless etc. Design concept of antennas is given, and experimental results are discussed.

A compact planar ultra-wideband (UWB) dipole antenna having band-notched characteristic is presented. The dipole antenna has the shape of a modified annular ring and is fed by a 50-Ω microstrip line. Cutting a slot in each radiating annular ring improves the input impedance bandwidth. With the design, the return loss is lower than -10 dB in 3.1 GHz-10.6 GHz frequency range. In addition, band-notched filtering properties in the 5.15 GHz-5.825 GHz are achieved by etching four rectangular slits in the ground plane, and the radiation pattern is similar to a conventional dipole antenna. A good agreement is found between the simulation and the experiment. Details of the proposed antenna design and the experimental results are presented.

A narrowband reflection and/or transmission filter made of heterostructured multilayer with two different ultrathin metallic films is proposed. The multilayer structure is a cascaded system that is formed by using two narrowband reflection-and-transmission filters. Each individual filter is made of an ultrathin metal film in front of a planar Fabry-Perot resonator. Using the transfer matrix method in a stratified system, the optical filtering properties are theoretically investigated and analyzed. It is found that the reflection peak at the design wavelength in the original individual filter becomes a dip in the heterostructured filter. The role played by the stack number of Bragg reflector in the design of narrowband filter is also clearly elucidated.

The T-matrix approach is effective in analyzing electromagnetic scattering from finite scatterers. Yet for scatterers with extreme geometry, this approach may fail. One example is its inability to analyze scattering from dielectric cylinders with large aspect ratios. To deal with such difficulty, recently we proposed a method based on an extension of the T-matrix approach, where a long cylinder is hypothetically divided into a cluster of identical sub-cylinders, for each the T matrix can be numerically stably calculated. Special care was paid to fulfill the boundary conditions at the hypothetic surface of any two neighboring sub-cylinders. The resultant coupled equations are different from that of multi-scatterer theory. The model results were in good agreement with experiment data available in the literature. However, the validity region of the proposed method was not fully characterized. Now we have developed and validated a method of moment (MoM) code, and are in a position to carry on the task of characterizing the validity region. The proposed method is found to be applicable to dielectric cylinders of arbitrary length as long as the T matrix is attainable for the elementary sub-cylinder. The conditions for the T matrix to be numerically stably calculated in terms of the equivalent volumetric radius and relative dielectric constant are also empirically obtained.

This paper derives its link of direction of arrival (DOA) and direction of departure (DOD) estimation problem for multi-input multi-output (MIMO) radar to the trilinear model. With the exploitation of this link, we present a trilinear decomposition-based blind algorithm for angle estimation in MIMO radar. After the algorithmic presentation and discussions for identifiability results, trilinear decomposition-based angle estimation under different array conditions has also been investigated. Our proposed algorithm works well without either spectral peak searching or pair matching, has better angle estimation performance than ESPRIT, and even supports small sampling sizes. Simulation trials testify that the merits of our algorithmic performance are in collaboration with theoretical findings.

This paper presents a novel spurious suppressed bandpass filter designed with triangular stepped-impedance resonators. The proposed resonators are folded for a triangular schematic, which creates two transmission zeros. By varying the line width of resonators, one of the zeros is tuned to suppress the first and second spurious responses, and the other is used to improve skirt selectivity. The current study analytically derives explicit design equations and fabricates a three-pole Chebyshev bandpass filter centered at 1.5 GHz based on the direct-coupled structure. The experimental results show spurious suppression improvement more than 20 dB up to 5.6 f₀.

A novel printed dual circular ring monopole antenna with low radar cross section (RCS) for ultra-wide band (UWB) application is proposed. The proposed antenna is designed to realize RCS reduction. The two circular rings are connected by several metallic via holes to improve the radiation characteristics of the proposed antenna. Its UWB-related characteristics are simulated and experimentally verified. The RCS performance of the proposed antenna under different loads is studied and compared with that of a commonly used circular-disc monopole antenna. The results show that the proposed antenna has good radiation performances and lower RCS than the reference antenna. The proposed antenna serves as a good candidate in the design of UWB antenna with the requirement of RCS control.