A hybrid method is proposed to compute the radar cross section (RCS) of multiple wire scatterers with an arbitrary orientation. Foldy-Lax equations in vector form are transformed into self-consistent equations for including the multiple scattering effects between scatterers. A thin-wire approximation of a method of moment (MoM) is used for calculating the scattering transition operator of a single wire scatterer. To verify the proposed method, two measurement models are fabricated and measured in a compact range chamber. The measured results agree well with the results of the proposed method.

The framework of our work is the application of a fast method to estimate the radiation pattern of an antenna from the measurement of the electric-field magnitude in the near-field region using infrared (IR) camera. IR acquisition techniques allows quasi-realtime measurements of the magnitude of the electrical field on planar surfaces in near-field conditions. However the antennas radiation patterns can only be estimated from near-field electrical magnitude and phase measurements. Consequently a classical plane to plane iterative phase retrieval process has been developed and tested with respect to a large number of configuration parameters such as to find an optimal configuration on a wide frequency range [0.5-20GHz]. In order to achieve and validate such a study, some comparisons have been performed on data obtained either by numerical simulation or classical near-field technique based upon radio-frequency (RF) probe scanning on simple horn antennas. Among all the studied parameters we will focus onto the influence of the dynamic range of the measurements on the reconstructed radiation patterns and on validations from experimental results.

In this study, the transmission of planar single-layer frequency selective surface (FSS) has been studied using modal analysis method, and the maximum transmission that a planar single-layer FSS structure with an infinitely thin array can reach is presented. The results show that this transmission upper limit is independent of the array and the element, which indicates that it is impossible to achieve a transmission higher than this upper limit under a given incident and dielectric-supporting condition by the design of the periodic array. As the modal analysis method is an accurate method to solve the scattering problem of planar FSS with an infinitely thin array, this upper limit is also independent of the solution method. Results of both numerical simulations and experiments show that the upper limit presented in this paper is strict, but may be hard to attain when FSS is supported by lossy dielectric mediums.

Diffraction of scalar plane waves by resistive surfaces are investigated by defining a new boundary condition in terms of the Dirichlet and Neumann conditions. The scattering problems of waves by a resistive half-plane and the interface between resistive and perfectly magnetic conducting half-planes are examined with the developed method. The resulting fields are plotted numerically. The numerical results show that the evaluated field expressions are in harmony with the theory.

In this work, the design studies of a 60 GHz, 100 kW CW gyrotron have been presented. Mode selection is carefully studied with the aim of minimizing mode competition and to yield a perfect solid beam output through an RF window with a suitable dimpled-wall quasi-optical launcher. Cavity design and interaction computations are then carried out. In addition, preliminary design of the magnetron injection gun, magnetic guidance system, launcher, and RF window are presented. Thus, we present a feasibility study, which indicates that the operation of such a gyrotron is possible and can give a power in excess of 100 kW at an efficiency > 35%. As a part of this work, a complete Graphical User Interface package "GDS V.01" (Gyrotron Design Suit Ver.01) has been developed for the design and conceptualization of specific gyrotrons.

A 40 A triode type magnetron injection gun for a 1 MW, 120 GHz gyrotron has been designed. The preliminary design has been obtained by using some trade-off equations. Computer simulation has been performed by using the commercially available code EGUN and the in-house developed code MIGANS. The operating voltages of the modulating anode and the accelerating anode are 60 kV and 80 kV, respectively. The operating mode of the gyrotron is TE_22,6 and it is operated in the fundamental harmonic. The electron beam with a low transverse velocity spread (δβ_⊥max = 3.3%) and velocity ratio, α = 1.38 at beam current = 40 A is obtained. The simulated results of the MIG obtained with the EGUN code have been validated with another trajectory code TRAK. The results obtained from both the codes are in good agreement. The sensitivity study has been carried out by changing the different gun parameters to decide the fabrication tolerance.

A compact tri-band planar monopole antenna suitable for 2.4/5.2/5.8 GHz WLAN and 3.5 GHz WiMAX is presented. The antenna employs a U-shaped parasitic strip and a defect ground-plane structure. By inserting a U-shaped strip as a parasitic strip into a normal monopole which operates at lower band of the WLAN, one more resonance at the higher WLAN band comes out. A defect ground-plane composed of two symmetrical L-shaped slits leads to another resonance operating at WiMAX band. The proposed antenna has a compact size of 22×41×0.8 mm³ and offers good radiation and reflection characteristics in the above frequency bands. The measured VSWR exhibits a good agreement with the simulated one. Detailed design steps, parametric studies and experimental results for the antenna are investigated in this paper.

In this paper, a circular slot antenna fed by an offset microstrip-fed line is proposed. The antenna exhibit dual-band characteristics. The two operating frequency bands are: 1.83--2.73 GHz and 5.36--7.63 GHz, which are of impedance bandwidth 39.5% and 34.9% respectively. The bands are suitable for PCS, UMTS, IMT-2000, ISM, Bluetooth, RFID and WLAN applications. A parametric study has been carried out by varying the location of the feedline to investigate its effect on the resonant frequency. Impedance, radiation and gain characteristics of the proposed antenna are also presented and discussed.

In this paper, a novel type of stacked microstrip patch antenna is presented in which fractal shaped defects have been excoriated from the patch surfaces. The antenna has been designed for dual band operation at the WLAN 2.4 GHz and 5.8 GHz frequency bands and size reduction for both the stacked patches is achieved due to the use of fractal shaped defects. The antenna was simulated using CST Microwave Studio 2010 and optimized using Particle Swarm Optimization (inbuilt in CST). The fabricated antenna's measurement results were found to be in good agreement with the simulated results.

In this paper, the Specific Absorption Rate (SAR) distribution in a human head irradiated by an obliquely incident electromagnetic plane wave is studied. A simple planar multi-layered structure is used to model the human head. Moreover, the steady state thermal elevation distribution is calculated by solving the bioheat equation using the finite difference time domain (FDTD) method. Both types of wave polarization (perpendicular and parallel) will be discussed. The obtained results confirm the importance of performing a thermal analysis along with the dosimetric one. It is found that the induced temperature elevation in the brain region, in all the examined conditions, never exceeds 0.4℃. This value is well below the threshold for the induction of adverse thermal effects to the neurons which is 3.5℃.

A power divider with ultra-wideband (UWB) performance has been designed. The quarter-wave transformer in the conventional Wilkinson power divider is replaced by an exponentially tapered microstrip line. Since the tapered line provides a consistent impedance transformation across all frequencies, very low amplitude ripple of 0.2 dB peak-to-peak in the transmission coefficient and superior input return loss better than 15 dB are achieved over an ultra-wide bandwidth. Two additional resistors are added along the tapered line to improve the output return loss and isolation. Simulation performed using CST Microwave Studio and measured results confirm the good performance of the proposed circuit. The return loss and the isolation between the output ports are better than 15 dB across the band 2-10.2 GHz. Standard off-the-shelf resistance values can be selected by optimizing the physical locations to mount the resistors. Better performance can be achieved with more isolation resistors added. Hence, the number of isolation resistors to be used may be selected based on the desired bandwidth and level of isolation and return loss specifications.

A compact ultra-wideband (UWB) bandpass filter (BPF) with dual notch bands is presented using a tri-layer structure. In the design of UWB BPFs, it is desired to have a uniform 3.1 GHz to 10.6 GHz full-band transmission response. Dual notch bands are generated to filter out the interferences caused by signals transmitted from WLAN and/or WiMAX systems at 5.8 GHz and 3.5 GHz, respectively. The sharp rejection of WiMAX signals is achieved by adding meander open-loop resonators on the middle layer. Another rejection of WLAN signals is introduced by adding a C-shaped resonator on the bottom layer. The proposed filter is not only realized theoretically but also verified by a full-wave electromagnetic simulation. The designed tri-layer UWB BPF with dual notch bands was fabricated by two FR4 printed circuit boards with the permittivity of 4.4 and the thickness of 0.8 mm. The total area is 11 mm×10.5 mm.

A very simple and more efficient CAD model is proposed to demonstrate the effect on input impedance characteristics based on cavity model analysis for wide range of variations of superstrate parameters and feed locations of an equilateral triangular microstrip patch antenna having different side lengths. The computed values are compared with different theoretical and experimental values available in open literature, showing close agreement. A Maxwell's equation solver is also used to validate our model.

In this paper, a high-e±ciency wireless energy transmission via magnetic resonance is implemented by using negative permeability metamaterial structures. The metamaterial structure is consisted of a three-dimensional (3D) periodic array of the unit cell that the capacitively loaded split ring resonators (CLSRRs) are periodically arranged in the cubic dielectric surfaces. This metamaterial structure has the negative permeability property that matches free space, which is used as a magnetic flux guide in order to enhance the efficiency of energy transmission between a source and distant receiving coil. The efficiency of energy transmission is improved as reducing the radiation loss by focusing the magnetic field to a distant receiving coil. The distance able to transport the energy with maintaining the same efficiency has been increased by the same mechanism. The efficiency of energy transmission is approximately 80% at a transmission distance of 1.5 m.

In this paper, we present a new ultra wideband antenna design with band rejection for UWB applications. A CPW-fed circular patch radiates through a circular aperture, which ensures wideband impedance matching and stable omnidirectional pattern over an UWB frequency range, from 3GHz to 10.6 GHz. In order to avoid interference with WLAN applications, at 5.8 GHz, the antenna is slightly modified to reject undesired band. A semi-circular slot ring is etched on the circular patch at the notch frequency, which creates an open circuit and avoids impedance matching and current propagation. A prototype was fabricated and measured, and the obtained experimental results agree with simulations and show an omnidirectional azimuth pattern over the entire bandwidth.

An improved finite-difference time-domain (FDTD) method is proposed for predicting transient responses of coaxial cables which are placed in an electrically large metallic cabin with arbitrary slots and circular windows on its wall. By integrating nodal analysis, multi-conductor transmission line (MTL) equation and FDTD method, we are able to accurately capture electromagnetic interference (EMI) effects on the cables. Our developed algorithm is verified by calculating frequency-dependent transfer impedance of coaxial cables together with induced currents. Numerical calculations are further performed to show the near-end coupled current responses of braided and tubular cables, respectively, and the effects of incident directions and polarizations of the illuminated electromagnetic pulse are both taken into account.

In this paper a modified version of the multi-band multiple ring monopole antenna is proposed. The height of the new design which consists of multiple half rings is half of the original one. The modified design is more attractive for low profile applications due to its lower height. The antenna is simulated and measured. It is shown that the simulation and measurement results are in good agreement. The performance of the modified version of the antenna is compared with the original design in terms of input characteristic and far field radiation patterns. It is shown that the multiband behaviour of the modified design is similar to the original one. However, there is a frequency shift between the operating bands of the new and the original antennas. The radiation patterns of the both antennas are similar to the conventional monopole antenna in lower operating frequency bands. However, degradation in radiation patterns of the both antennas is observed as frequency increases.

An analytical method for evaluating pole-residues in spectral method of moments (MoM) formulations is presented. Spectral integral formulations for periodic structures involve the inverse of the MoM matrix, which exhibits a periodic set of pole singularities, corresponding to the zeros of the matrix's determinant. So far, these singularities have not been extracted and the corresponding pole-residues were calculated directly from the differential or integral definitions of the residue. In this work, we consider an analytical expression for the solution to the MoM matrix equation, which enables the extraction of pole singularities and the analytical evaluation of pole-residues. We also present a comparison to previous methods.

The classical electrodynamics allows the use of retarded electromagnetic fields. The purpose of this investigation is to predict the useful force in a coil-ring system by electromagnetomechanical conversion. Analytical equations in retarded regime are given and are used to simulate a realistic thruster based on the coil-ring system. It is shown that a net force in the inertial coil-ring system is created. By means of high frequency electronics, analytical and practical tools toward new experiments for electromagnetic thrusters are given.

This paper presents a numerical simulation of the human head coupling with a Planar Inverted-F Antenna (PIFA) structure based on the Coupled Integral Equation/Method of Moment (CIE/MoM) approach to study the effects of the EM coupling on the antenna performance. A mix-potential integral equation (MPIE) for the surface current of PIFA structure and a volume electric field integral equation (VEFIE) for the head with mutual coupling terms are obtained. Finally numerical results will be presented at 900 and 1800 MHz for the antenna performance parameters. The validity of the proposed method is evaluated using the XFDTD software.