A polarization reconfigurable spiral slot antenna with polarization states switched among left-hand circular polarization (LHCP), right-hand circular polarization (RHCP) and linear polarization (LP) is proposed in this paper. The antenna consists of a coplanar waveguide (CPW) input, a pair of reconfigurable CPW-to-slotline transitions, two separated same size single-arm spiral slot radiators, and four PIN diodes for reconfigurability. A good impedance match (VSWR≤2) for both linear and circular polarization is achieved from 2.1 to 2.9 GHz. The bandwidth for axial ratio AR≤3 dB for both RHCP and LHCP states ranges from 2.27 to 2.66 GHz (15%). The simulation and measurement results agree well and hence sustain the reconfigurability of the proposed design.

A design procedure for microstrip antenna topologies operating within the full UWB band is described. The presence of the full ground plane successfully results in a unidirectional antenna, which is important in applications related to Wireless Body Area Networks (WBAN). The existing broadbanding concepts have been creatively combined throughout the design to enable the UWB behavior, while simultaneously keeping the full ground plane intact. The procedure is validated with a concrete design of a microstrip type UWB antenna operating from 3.6 GHz to 10.3 GHz.

To cope with the energy shortage and the rising cost of the fossil fuel, many wind farms are being constructed under the supervision of Korean government along the coasts of Korean peninsula to generate clean and renewable energy. However, construction of these wind farms may cause negative effect on various L-band radars in operation. This paper presents the result of the micro-Doppler (MD) analysis of the influence of the wind turbine on the L-band radar using the point scatterer model and the radar cross section of the real turbine predicted by the method of physical optics. The simulation results obtained at three observation angles show that the range of MD occupies a considerable portion of the helicopter MD range, and thus, the operations using helicopters need to be avoided in the wind farm region, and additional radars are required for the recognition of helicopter-like objects.

A novel Frequency Selective Surface (FSS) configuration is proposed for the design of polarization-insensitive metamaterial absorbers operating below 1 GHz, where the first resonances of small commercial enclosures appear. The novel FSS shows a strong subwavelength response, enhanced by the dielectric substrate, which allows the design of compact planar absorbers with excellent angular and polarization stability.

This paper proposes an investigation in the terahertz (THz) frequency range of the dispersion and an individual quantitative treatment of the losses of the most classical microwave waveguides (coplanar, slotline, microstrip and stripline) numerically led in three dimensions (3D). An original strategy has been used to quantify radiation losses associated with leaky modes. A very low THz permittivity polymer (benzocyclobutene (BCB)) was used as a very convenient substrate to be easily grafted as a THz environment of integrated passive or/and active devices. Direct comparisons of the losses and the dispersion have been performed following two criteria: a constant characteristic impedance Z_c fixed at 100 Ω and a constant effective width Weff fixed at 30 μm. The best waveguides are microstrip (α_T= 2.52 dB/mm for Z_c= 100 Ω and for W/H=35/50 μm (with W the strip width and H the substrate height) and α_T =2.29 dB/mm for W_eff = 30 μm at 1 THz with H = 30 μm) and stripline (with quasi-null radiation losses and the best quality factor Q_T= 63 for Z_c = 100 Ω). The large dispersion and radiation losses of the slotline (SL) can be reduced with a thick BCB encapsulation to enhance the THz signal. The coplanar waveguide (CPW) remains in a medium position. Besides the parasitic mode (SL) and low Q_T problems due to mainly ohmic losses, its major advantage is its planar geometry allowing to an easy circuit integration with THz sources, amplifiers and detectors based on semiconductor. Consequently, these THz studies on BCB microwave standard waveguides open to various perspectives to carry out a broad panel of integrated THz circuits.

Two multi-band filters operating in the 1-10 GHz range are designed, analytically studied and experimentally verified. The filters are developed by making modifications to a series capacitively coupled, microstrip line filter. The middle section of the microstrip line is widened and rectangular slots are etched on it. Widening increases the effective dielectric constant which helps in miniaturization of the circuit. On the other hand, the rectangular slot cause various longitudinal, transverse and slot mode resonances to be excited resulting in multi-band operation. An extensive parametric analysis with respect to the physical parameters of the filter leading to the development of a semi-empirical model is presented. The model can be used to predict the resonant frequencies with sufficient accuracy for a given geometrical structure. The model also predicts the limit of miniaturization achievable with the presented design. The proposed filters besides being compact have good out of band rejection and are easy to design and fabricate without the need of additional matching circuits.

By combining the work of J.R. Wait on a periodically loaded vertical wire grid and the work of D.A. Hill and J.R. Wait on a wire mesh, a novel generalized formulation, the Wait-Hill formulation, is obtained for the analysis of lumped-element periodically-loaded orthogonal wire grid generic frequency selective surfaces. The Wait-Hill formulation is simple and not restricted by the miniaturization assumption of current approximate simple methods for the analysis of loaded and unloaded wire grids. The results of the Wait-Hill formulation are shown to agree well with those of a commercial software.

Results of a self-consistent computational analysis based on a mathematical model of resonance scattering and generation of waves on an isotropic nonmagnetic nonlinear layered dielectric structure excited by a packet of plane waves are presented, where the analysis is performed in the domain of resonance frequencies. Physically interesting properties of the nonlinear permittivities of the layers as well as their scattering and generation characteristics are obtained, for instance the characteristic dynamical behaviour of the relative Q-factor of the eigenmodes and the energy of higher harmonics generated by canalising as well as decanalising nonlinear layers. The results demonstrate the possibility to control the scattering and generating properties of a nonlinear structure by means of the excitation intensities.

This paper describes an experimental model for the characterization of electromagnetic phenomena that occur in the end regions of large turbo-generators. The study is based on a test bench that contains a stack of steel laminations from a 900 MW turbogenerator stator and two exciting circuits in order to combine a transverse magnetic flux with the in-plane flux. In order to explain the flux penetration within the magnetic sheet stack, accurate experimental measurements are performed. Results are compared with the finite element simulations using code_Carmel3D. In the same time, theoretical and experimental results are analyzed with a view to examining the influence of transverse flux on additional losses.

There has been a surge of interest in the subwavelength confinement effects of the electromagnetic fields. Based on these effects, one can obtain new behaviors of the near- and farfield radiation. It is well known that in optics, the subwavelength confinement can be obtained due to surface-plasmon (or electrostatic) oscillations in metal structures. This paper is a review of recent studies on the subwavelength confinement in microwaves due to magnetic-dipolarmode (MDM) [or magnetostatic (MS)] oscillations in small ferrite samples. MDM oscillations in a mesoscopic ferrite-disk particle are quantized oscillations, which are characterized by energy eigenstates. The field structures are distinguished by power-flow vortices and non-zero helicity. Also in vacuum, the near fields originated from MDM particles are designated by topologically distinctive power-flow vortices, non-zero helicity, and a torsion degree of freedom. To differentiate such field structures from regular electromagnetic (EM) field structures, we term them as magnetoelectric (ME) fields. In a pattern of the microwave field scattered by a MDM ferrite disk and MDM-disk arrays, one can observe rotating topological-phase dislocations. This opens a perspective for creation of engineered electromagnetic fields with unique symmetry properties. In the near-field applications, we propose novel microwave sensors for material characterization, biology, and nanotechnology. Strong energy concentration and unique topological structures of the near fields originated from the MDM resonators allow effective measuring chiral properties of materials in microwaves. Generating far-field orbital angular momenta from near-field microwave chirality of MDM structures can be a subject of a great interest. Realization of such vortex generators opens perspective for novel microwave systems with topological-phase modulation.

In this paper, the integrated formulas for the electromagnetic field in the planar boundary between isotropic and onedimensionally anisotropic media due to a horizontal electric dipole situated on the interface are treated in detail, and the calculable field components are given in terms of series that involve confluent hypergeometric functions, namely, the Fresnel and exponential integrals, and the expressions are more complex than the isotropic case. The exact expressions and simplified formulas can be easily reduced to the corresponding isotropic case. The results are useful to study the propagation of the electromagnetic waves on the boundary of one-dimensionally anisotropic earth or sediments.

The analysis and design of the multi-element coupled lines, in conjunction with the junction discontinuity effect, is presented, and its applicability in high power rf regime is discussed. Junctions are usually employed to connect two different coupled elements, which gives rise to undesirable reactance i.e. junction discontinuity effect. These effects are found prominent in the high power coupled lines for HF and VHF applications because of its large structural dimensions. The design and simulation of 3-element, 8.34±0.2 dB coupled line section rated for 38 to 112 MHz and 200 kW has been performed. The simulated results are significantly deviated from the theoretically calculated ones where the discontinuity effect is usually ignored. A generalized theoretical procedure is developed to take into account the effect of junction discontinuity at the designing stage. The theory is applied to the 3-element 8.34±0.2 dB coupled-line section, and simulation is performed by using standard Ansoft HFSS software. The HFSS simulation results are in close agreement with the theoretical predictions.

Microwave pyrolysis overcomes the disadvantages of conventional pyrolysis methods by efficiently improving the quality of final pyrolysis products. Biochar, one of the end products of this process is considered an efficient vector for sequestering carbon to offset atmospheric carbon dioxide. The dielectric properties of the doping agents (i.e., char and graphite) were assessed over the range of 25°-400°C and used to develop a finite element model (FEM). This model served to couple electromagnetic heating, combustion, and heat and mass transfer phenomena and evaluated the advantages of selective heating of woody biomass during microwave pyrolysis. The dielectric properties of the doping agents were a function of temperature and decreased up to 100°C and thereafter remained constant. Regression analysis indicated that char would be a better doping substance than graphite. The simulation study found that doping helped to provide a more efficient heat transfer within the biomass compared to non-doped samples. Char doping yielded better heat transfer compared to graphite doping, as it resulted in optimal temperatures for maximization of biochar production. The model was then validated through experimental trials in a custom-built microwave pyrolysis unit which confirmed that char doping would be better suited for maximization of biochar.

A transient finite-element model has been presented to simulate extracellular potential stimulating in a neural tissue by a nonplanar microelectrode array (MEA). This model allows simulating the extracellular potential and transmembrane voltage by means of a single transient computation performed within single finite element (FE) software. The differential effects of the configuration and position of MEA in electrical extracellular stimulation are analyzed theoretically. 3-D models of single nerve fiber and different MEA are used for the computation of the stimulation induced field potential, whereas a cable model of a nerve fibre is used for the calculation of the transmembrane voltage of the nerve fiber. The position of MEA and the spacing of the microelectrodes are varied while mono-, bi-, tri-, and penta-polar MEAs are applied. The model predicts that the lowest stimulation voltage threshold is obtained in the stimulation with penta-polar MEA. Moreover, the relationships, which exist between the thresholds of the electrical extracellular stimulation and the parameters including position of the electrode array and the spacing of the microelectrodes in array, are studied and obtained.

A high-efficiency rigorous approach for the solution of the two-dimensional Laplace equation with Dirichlet's boundary conditions is developed to tackle electrostatic problems involving metallic cylinders of arbitrary cross-sections. In this paper we demonstrate how this novel algorithm can be used to address the problems arising in the capacitance microscopy to provide a higher resolution in studies of micro-cavities and whiskers on the surface of metallic samples. The precise capacitance images of the probe/sample systems are presented.

A passive millimeter-wave imager BHU-2D-U based on synthetic aperture interferometric radiometer (SAIR) technique has been developed by Beihang University. The imager is designed for detecting concealed weapons on human body and operated under the near-field condition of the antenna array, thus the conventional Fourier imaging theory does not apply. In this paper, an accurate numerical image reconstruction algorithm using regularization theory is proposed. By means of adding a prior information of desired brightness temperature image, the influences of measurement noise and focusing error on the reconstructed image have been reduced. Numerical simulations and experiments on BHU-2D-U have been performed to verify the superiorities of the proposed algorithm over the corrected Fourier method and the Moore-Penrose pseudo inverse method. The results demonstrate that the proposed method is an advantageous imaging algorithm for near-field millimeter-wave SAIR.

In this paper, the synthesis of sparse time-modulated linear arrays with minimum number of elements and controlled harmonic radiations is investigated. The proposed iterative approach based on a particle swarm optimization is aimed at finding the array configuration with the minimum number of elements and the optimal pulse sequence that affords a beam pattern with the same features of a reference one also limiting the amount of sideband radiations under a specific threshold. A set of representative numerical examples are discussed to assess the effectiveness and the reliability of the proposed approach.

A broad-band transmission line spatial power combiner (SPC) is proposed in this paper, which uses a square coaxial (Squarax) transmission line (TL). This structure has some advantages over the traditional circular coaxial spatial power combiner, which have been described in this paper. Fin-Line to microstrip transitions are inserted into the Squarax TL, in order to allow an easy integration of Monolithic Microwave Integrated Circuit (MMIC) Solid State Power Amplifier (SSPA). The Squarax SPC geometry allows the feeding of a higher number of MMIC than in a Waveguide SPC, so that this structure ensures high power outputs and small sizes, together with theoretical DC frequency cut-off. In this work, the design and simulation of a passive 4-18 GHz Squarax SPC are reported.

In this paper, an ultra-wideband (UWB) patch antenna integrated with a dielectric resonator is proposed for cognitive radio applications. The patch antenna is fed by a coplanar waveguide (CPW) line, and it consists of a rectangular monopole having an elliptical base, and operates from 2.44 to 12 GHz, this UWB antenna is intended to collect the information. Moreover, the proposed structure integrates a narrow-band rectangular dielectric resonator antenna (RDRA) for operation, with very good isolation between the two ports (transmission coefficient S₂₁ less than -20 dB). The RDRA provides a bandwidth from 5.23 GHz to 6.11 GHz. The electromagnetic analysis is carried out using tow commercial software tools. Furthermore, to validate the proposed concept, experimental measurements are also performed.

A planar inverted F antenna is combined with passive (reactively loaded) elements in order to implement a multi-frequency configuration appropriate for biomedical applications in microwave frequencies. A case study of an electronically Reconfigurable PIFA (R-PIFA) is pursued for the detection of temperature abnormalities in human tissue phantom using microwave radiometry, where the performance of the structure is optimized with respect to input impedance matching in multiple frequencies. The optimization of the array is performed using a Genetic Algorithm (GA) tool as a method of choice. Due to its limited physical size, the proposed R-PIFA can also be used as a portable antenna system for deployment in mobile medical applications.