Microwave tomography deserves attention in biomedical imaging, owing to its potential capability of providing a morphological and functional assessment of the inspected tissues. However, such a goal requires the not trivial task of solving a non linear inverse scattering problem. In this paper, the factors affecting the complexity of the inverse problem are exploited to trace guidelines aimed at setting the matching fluid, the frequency range and the number of probes in such a way that the dielectric parameters of female breast tissues can be reliably retrieved. Examples, concerning 2D realistic numerical phantoms obtained by NMR images, are given to asses a osteriori the effectiveness of the proposed guidelines.

In this paper, a new technique is proposed for field effect transistor (FET) small-signal modelling using neural networks. This technique is based on the combination of the Mel frequency cepstral coefficients (MFCCs) and discrete sine transform (DST) of the inputs to a neural network. The input data sets to traditional neural systems for FET small-signal modelling are the scattering parameters and corresponding frequencies in a certain band, and the outputs are the circuit elements. In the proposed approach, these data are considered as forming random signals. The MFCCs of the random signals are used to generate a small number of features characterizing the signals. In addition, other MFCCs vectors are calculated from the DST of the random signals and appended to the MFCCs vectors calculated from the signals. The new feature vectors are used to train the neural networks. The objective of using these new vectors is to characterize the random input sequences with much more features to be robust against measurement errors. There are two benefits for this approach: a reduction in the number of neural networks inputs and hence a faster convergence of the neural training algorithm and robustness against measurement errors in the testing phase. Experimental results show that the proposed technique is less sensitive to measurement errors than using the actual measured scattering parameters.

In this paper, we propose a novel genetic algorithm (GA) called immunity GA (IGA) for array pattern synthesis with interference suppression using digital amplitude only control. The IGA is based on crossover evolution where the crossover operator is a variant of the known GA operator. A new formulation of the array factor transform for a specific number of elements N is expressed by a discrete cosine transform (DCT) with pre-computed DCT matrix. Evaluating thousands of candidate solutions generated by the IGA using the precomputed DCT matrix will result in a high speed computation. This high performance allows us to find a good approximation of the absolute minimum SLL of synthesized arrays with digital amplitude control. Simulation results show the effectiveness of this new algorithm for pattern synthesis with low SLL and null steering.

A sensing device comprising of a parabolic reflective surface and a bi-conical metal structure is proposed to focus terahertz energy on sample material in the sensing zone to create a strong interaction between terahertz signals and the sample under test. The signal enhancement by the sensing device is confirmed by modeling and simulation results. The proposed sensor is applied to investigate the polarization dependency of a split ring resonator (SRR), and spectral signatures of the SRR under different incident wave polarizations are obtained.

A compact ultra-wideband (UWB) planar monopole antenna is proposed. Multiple trapezoids and a semicircle are connected to form the patch of the monopole. The compact antenna not only has low return loss, but also has omni-directional radiation pattern over the ultra-wide bandwidth. Both the simulated and measured results are given and they are in reasonable agreement. The group delay, which is an indication of linearity between two proposed antennas, is also good. Parametric analysis on the patch shape has been performed to give some helpful design information.

This paper presents a microwave imaging method for malignant tumors using flanged parallel-plate waveguide probes, based on detecting the significant difference in complex permittivity that exists between the tumor and its surrounding tissues. The presence of a tumor is identified from a frequency scan of the resonant scattering parameters. The tumor location can be estimated using S₂₁ obtained at various positions of the region of concern, e.g. human organ, biological tissues, etc., while another probe transmits at the position yielding maximum resonating response of S₁₁, with triangulation technique. A tumor can also be distinguished from clutter items. With specific reference to the detection of breast cancer, simulation studies are presented to verify the performance of this probe and the proposed detection technique.

It is known that with restrictions on the type of the constitutive equations, Maxwell's equations in non-uniform media can sometimes be reduced to two 2nd order differential equations for 2 scalar quantities only. These results have previously been obtained in two quite different ways, either by a "scalarization of the sources", where the relevant scalar quantities are essentially vector potential components, and the derivation was limited to isotropic media, or alternatively by using the "scalar Hertz potentials", and this method has been applied to more general media. In this paper it is shown that both methods are equivalent for gyrotropic media. We show that the scalarization can be obtained by a combination of transformations between electric and magnetic sources and gauge transformations. It is shown that the method based on the vector potential, which previously used a non-traditional definition of the vector potentials, can also be obtained using the traditional definition provided a proper gauge condition is applied and this method is then extended from isotropic to gyrotropic media. It is shown that the 2 basic scalar Hertz potentials occurring in the second method are invariant under the source scalarization transformations of the first method and therefore are the natural potentials for obtaining scalarization. Finally it is shown that both methods are also equivalent with a much older third method based on Hertz vectors.

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.