The resonance frequency of Split-Ring Resonators (SRRs) loading a microstrip transmission line was tuned by means of a Ba_0.5Sr_0.5TiO₃ (BST) ferroelectric thin film. For a bias of 30 Volts, we obtained a band-stop response with a shift around 7% of the resonance to higher frequencies in Ku band. The originality of the device under test is (i) the utilisation of single C-shaped SRRs, (ii) the localisation via chemical etching of the BST film to voltage controlled interdigitated capacitances and (iii) the enhancement of the operating frequency (around 17 GHz).

We present exact three-dimensional semi-analytical expressions of the force exerted between two coaxial thick coils with rectangular cross-sections. Then, we present a semi-analytical formulation of their mutual inductance. For this purpose, we have to calculate six and seven integrations for calculating the force and the mutual inductance respectively. After mathematical manipulations, we can obtain semi-analytical formulations based on only two integrations. It is to be noted that such integrals can be evaluated numerically as they are smooth and derivable. Then, we compare our results with the filament and the finite element methods. All the results are in excellent agreement.

In this paper an inverse source problem is investigated. The measurement set-up is a reflector antenna covered by a radome. Equivalent currents are reconstructed on a surface shaped as the radome in order to diagnose the radome's interaction with the radiated field. To tackle this inverse source problem an analysis of a full-wave integral representation, with the equivalent currents as unknowns, is used. The extinction theorem and its associated integral equation ensure that the reconstructed currents represent sources within the radome. The axially symmetric experimental set-up reduces the computational complexity of the problem. The resulting linear system is inverted by using a singular value decomposition. We visualize how the presence of the radome alters the components of the equivalent currents. The method enables us to determine the phase shift of the field due to the transmission of the radome, i.e., the IPD (insertion phase delay). Also, disturbances due to defects, not observable in the measured near field, are localized in the equivalent currents.

A set of algorithms, specifically developed to facilitate an effective modeling of fractal-boundary microstrip antennas in the analysis of such structures through numerical electromagnetic (EM) solvers is presented in this paper. A fractal generator based on the implementation of an Iterated Function System (IFS) produces the geometry specified in accordance with the user-defined input parameters. The structure is created through a solver-specific interface and is thus applicable to a commercially available EM simulation suite. The generation of specific shapes through these algorithms provides a flexible method to study different geometries without the need to modify either the interface or the solver. Three structures based on the Minkowski fractal obtained through these techniques have been studied using two EM solvers for comparison. The frequency-domain results show good agreement between the two solvers, thus validating the algorithms implemented. Complex structures with higher iterations can be studied using these algorithms.

A model for two-dimensional layered medium is proposed for through-wall imaging problem. It is integrated with the subspace-based optimization method for reconstructing the relative permittivity profile in a fast and robust manner. Numerical results have shown that the concealed targets within walls can be reconstructed well using the proposed model even though full aperture of targets is not available due to the presence of walls. The model has also been employed for studying the effect of the presence of walls on imaging.

In this paper, we present a new dual band planar antenna. The proposed antenna consists of a microstrip patch with a U-shaped slot that is fed by a broadband electromagnetic coupling probe, known as L-probe. Radiation characteristics of the antenna and different methods for control of the resonant frequencies are investigated.

This paper presents microstrip array antenna integrated with novel shapes of 2D-electromagnetic band-gap structure (2D-EBG). Three different shapes of 2D EBG are used for harmonic suppression, optimizing the current distribution on the patches and decreasing the mutual coupling between array elements. As a result, the performance of the antenna array is improved. The three novel shapes of 2D-EBG presented are star, H shaped and I shaped slots. Simulated and measured results verify the improved performance of the array antenna compared to the antenna without EBG as well as antenna array with conventional EBG shapes. The harmonic suppression and reflection coefficients are improved by about 18 dB. Minimum mutual coupling is less than -20 dB, and the antenna size is reduced by 15% compared to the original size.

Two novel designs for compact reconfigurable antennas are introduced for wireless communication devices. These designs solve the steering frequency problem by tracking the desired resonance frequency or by generating various operating frequency bands to be selected electronically. In the first design, the length of the rectangular defected ground structure (RDGS) is electrically adjusted to change the resonant frequency of the MPA. While in the second design different turns of spiral AMC ground plane generate frequency bands, or modes, that are selected/optimized to serve different communication systems simultaneously. These systems may include various combinations of bluetooth, S-band and wireless local-area network (WLAN). These designs have several advantages as the total antenna volume can be reused, and therefore the overall antenna will be compact, although, the radiation of the MPA is kept fixed without any degradation. The designs are verified through both numerical simulations and measurement of a fabricated prototype. The results confirm good performance of the single and multiband reconfigurable antenna designs.

This paper studies optical solitons, in presence of higher order dispersion terms by the aid of He's semi-inverse variational principle. Both Kerr law and power law are taken into consideration. The numerical simulations are also given to complete the analysis.

Up to now, the terahertz (THz) band is still an unexplored region in the sense that no practical application exists. New operating principles by traveling wave concept should be, therefore, appreciated for the real applications. In this paper, the generalized three-dimensional (3D) transverse magnetic (TM) mode analysis to analyze the characteristics of two-dimensional electron gas (2DEG) drifting plasma at the III-V high-electron-mobility-transistor (HEMT) hetero-interface such as AlGaAs/GaAs hetero-interface and its interaction with propagating electromagnetic space harmonic wave is presented. It includes, (1) the determination of electromagnetic fields in semiconductor drifting plasma using the combination of well-known Maxwell's equations and carrier kinetic equation based on semiconductor fluid model and the derivation of the effective permittivity of drifting plasma in 2DEG on semi-insulating substrate, and (2) the analysis to describe the presence of interactions using a so-called interdigital-gated HEMT plasma wave devices. To describe the interaction, the admittance of the interdigital gate is evaluated. The numerical procedures to solve the integral equations which are used in determining the admittance is explained. A negative conductance is obtained when drifting carrier velocity is slightly exceed the fundamental wave velocity indicates the significant condition of the interaction. A brief analysis and discussion on the Dyakonov-Shur THz surface wave in 2DEG is also presented.

Wide-band hybrid amplifier is theoretically proposed using a series configuration of Thulium-doped fiber amplifier (TDFA) and fiber Raman amplifier (FRA), which using the similar type of pump laser. The operating wavelength of this amplifier covers the bandwidth of entire short wavelength band (S-band) region by combining the gain spectrum of TDFA and FRA. The theoretical gain varies from 20 to 24 dB within a wavelength region from 1460 to 1525 nm and which is in a good agreement with the experimental result. The development of reliable high-power diode lasers in the 1420 nm wavelength range will make this type of wide-band hybrid amplifier an interesting candidate for S-band optical telecommunication systems.

This paper investigates the properties of the on-wafer coupled interconnects built in a 0.18 μm CMOS technology for RF applications. A SPICE compatible equivalent circuit model is developed. The proposed model is an extension of a 2-Ⅱ equivalent circuit model for single-line interconnects by adding two coupling components. The model parameters are extracted from four-port S-parameter simulation results through a calibrated electromagnetic (EM) simulator, i.e. HFSS. The accuracy of the model is validated from 500 MHz to 20 GHz.

We propose a mode based approach for developing a parametric model to characterize RF propagation in conduits. The model considers a conduit as a lossy waveguide and defines the total received power as the sum of powers excited in propagating modes. The model's parameters are estimated from both the physical properties of the conduit material and an empirical data set. Underground conduits have significant value as wireless communication channels for condition based monitoring within the conduit. An enabler for this wireless sensor network application is based on characterizing the expected coverage range of wireless transceivers operating in the 2.4 GHz ISM band. Previous studies on modeling RF propagation in underground conduits have focused on conduits with diameters larger than 1.05 m. This motivated our measurement campaign to collect empirical data from underground conduits with varying diameters from 0.30 m to 1.37 m. The empirical data is used to predict the mode coupled powers which are model parameters that are analytically intractable. We observe that the proposed model provides a good estimate of received power in terms of contribution from dominant propagating modes.

A novel approach is proposed for automated dimension estimation in memory polynomial based power amplifiers/transmitters behavioral models. This method consists of successively identifying the static nonlinearity order and memory depth of the model in accordance with a predefined performance criterion. The proposed method is validated using a 3G Doherty power amplifier driven by various WCDMA signals. Experimental results demonstrate the robustness of the proposed successive sweep approach compared to the conventional blind simultaneous sweep approach. The proposed dimension estimation method is an enabling tool for efficient design optimization of power amplifiers circuits to enhance their linearizability.

An effective approach to characterize frequency-dispersive sheet materials over a wide RF and microwave frequency range based on planar transmission line geometries and a genetic algorithm is proposed. S-parameters of a planar transmission line structure with a sheet material under test as a substrate of this line are measured using a vector network analyzer (VNA). The measured S-parameters are then converted to ABCD matrix parameters. With the assumption of TEM/quasi-TEM wave propagation on the measured line, as well as reciprocity and symmetry of the network, the complex propagation constant can be found, and the corresponding phase constant and attenuation constant can be retrieved. Attenuation constant includes both dielectric loss and conductor loss terms. At the same time, phase term, dielectric loss and conductor loss can be calculated for a known transmission line geometry using corresponding closed-form analytical or empirical formulas. These formulas are used to construct the objective functions for approximating phase constants, conductor loss and dielectric loss in an optimization procedure based on a genetic algorithm (GA). The frequency-dependent dielectric properties of the substrate material under test are represented as one or a few terms following the Debye dispersion law. The parameters of the Debye dispersion law are extracted using the GA by minimizing the discrepancies between the measured and the corresponding approximated loss and phase terms. The extracted data is verified by substituting these data in full-wave numerical modeling of structures containing these materials and comparing the simulated results with experimental.

In the paper the unified design procedure for planar dipoles oriented on UWB application is proposed. The procedure leads to obtain a good matching characteristic of planar dipoles in UWB frequency band. The design process is split into two parts: the radiator and the balun design. The Radiator Quality Factor (RQF) is defined as an evaluation suitability of planar radiators to be matched in UWB frequency band. Based on RQF, the optimal circular radiator is chosen, and the whole dipole antenna is designed. The general algorithm of antenna design is formulated and utilised in the planar dipole with elliptical arms project. Two antennas, with circular and elliptical arms, have been fabricated and measured in order to verify the design procedure. Both antennas are characterized by the reflection coefficient less than -10 dB from 2 GHz up to 14 GHz.

A new, approximate, uniform geometrical theory of diffraction (UTD) based ray solutions are developed for describing the high frequency electromagnetic (EM) wave radiation/coupling mechanisms for antennas on or near a junction between two different thin planar slabs on ground plane. The present solution is obtained by extending the normal incidence solution in order to treat the more general case of skew (or oblique) incidence (three-dimensional 3-D). Plane wave (for oblique or skew incidence) and spherical wave illumination are all considered in this work. Unlike most previous works, which analyze the plane wave scattering by such structures via the Wiener-Hopf (W-H) or Maliuzhinets (MZ) methods, the present development can also treat problems of the radiation by and coupling between antennas near or on finite material coatings on large metallic platforms. In addition, the present solution does not contain the complicated split functions of the W-H solutions nor the complex MZ functions. Unlike the latter methods based on approximate boundary conditions, the present solutions, which are developed via a heuristic spectral synthesis approach, recover the proper local plane wave Fresnel reflection and transmission coefficients and surface wave constants of the material slabs. There is a very good agreement, with less than ± 1 dB differences when the numerical results based on the presented UTD solution for a material junction are compared with that of the MZ solution.

By taking inspiration from [1], a synthesis strategy is proposed for the case of planar arrays and ring shaped patterns which does not require the exploitation of global optimization procedures. In particular, the approach is able to determine a priori (that is, without solving the overall design problem) whether the given power pattern design constraints can be fulfilled or not, and, in the affirmative case, to determine the needed excitation coefficients. Although the approach does not apply to generic planar arrays and generic constraints, it may serve both as a reference solution for more general synthesis procedures, and as an elementary brick for more cumbersome synthesis problems.

A general domain decomposition scheme based on the use of complex sources is presented for the electromagnetic analysis of complex antenna and/or scattering problems. The analysis domain is decomposed into separate subdomains whose interactions are described through a network formalism, where the ports are associated with complex point source (CPS) beams radially emerging from the subdomain boundaries. Each obstacle is independently analyzed with the most appropriate technique and described through a generalized scattering matrix (GSM). Finally, a linear system is constructed, where the excitation vector is given by the complex source expansion of the primary sources. Thanks to the angular selectivity of the CPS beams, the subdomain interactions only involve a small fraction of the beams; thus, yielding sparse moderate size linear systems. Due to the re-usability of the GSMs, the proposed approach is particularly efficient in the context of parametric studies or antenna installation problems. Numerical examples are provided to demonstrate the efficiency and the accuracy of the proposed strategy.

A new approach to design digitally tunable optical filter system for DWDM (Dense Wavelength Division Multiplexed) optical networks is presented. This digitally tunable optical filter system uses semiconductor optical amplifiers (SOAs) and DWDM thin film filter based wavelength selection elements. The design is very easy to configure, expand and reduce. This digitally tunable optical filter system is smaller in size, lesser in weight, cheaper in costt, consumes low power and has better timing performance as compared to digitally tunable optical filter suggested by researchers recently.