Compact dual-mode dual-band bandpass filters are realized with a single periodic stepped-impedance ring resonator. Neither extra resonator nor substrate layer is required for implementing the second passband. Based on the transmission line theory, a transmission zero design graph consisting of the transmission zeros together with the resonant frequencies of the resonator is developed against the space separation angle between the input and output ports. Based on this graph, when the line-to-ring feed structure is implemented, the space angle can be determined for the dual-mode dualband design with designated zeros near the two passbands. It is believed that this is the first design graph for designating the transmission poles and zeros of a dual-mode ring resonator filter before the excitation structure is realized. Three dual-mode dual-band bandpass filters are carried out for demonstration. All circuits occupy only 60% of the area of the conventional ring resonator bandpass filter at the first frequency. Measured results of experimental circuits show good agreement with simulated responses.

An analysis has been presented by means of mode matching method for two microwave cavities of different sizes which are fed by TE10 waveguide and which are loaded with lossy dielectric slab type material. The accuracy of the results obtained is presented together with the comparison of the results which are obtained by HFSS numerical method. The optimization of the load location has been performed in order to maximize the electrical field on the material. The principle of this optimization is based on finding the existence of the positions in which S11 reflection coefficient is the lowest. When the feeding guide for the two different microwave cavities is entirely at the centre of the resonator, the reflection coefficient distribution change has been detected according to the different positions of the material in the oven, and then the lowest positions have been found out. The electric field changes in the detected positions have been recorded.

A Message Passing Interface (MPI) parallel implementation of a hybrid solver that combines the Method of Moments (MoM) with higher order basis functions and Physical Optics (PO) has been successfully used to solve a challenging problem including a 2160-slot waveguide array on an airplane with a maximum dimension larger than 1000 wavelengths. The block-partitioned scheme for the large dense MoM matrix combined with the process-cyclic scheme for the PO discretized triangles is designed to achieve excellent load balance and high parallel efficiency. To break the limitation of physical memory, the parallel out-of-core technique is introduced to tackle large dense systems generated using the MoM formulation. This research provides a solution with reasonable accuracy for solving large on-board antenna problems but has very low memory usage.

A novel technique of the electric- or E- field extraction from the magnetic- or H- near-field in timedomain is reported. This technique is based on the use of the Maxwell-Ampere relation associated to the plane wave spectrum (PWS) transform. It is useful for the E-near-field computations and measurements which are practically complicated in time-domain in particular, for the EMC applications. The considered EM-field radiation is generated by a set of electric dipoles excited by an ultra-short duration current having frequency bandwidth of about 10-GHz. The presented EM-field calculation technique is carried out by taking into account the evanescent wave effects. In the first step, the time-dependent H-field data mapped in 2-D plan placed at the height z₀ above the radiating devices are transposed in frequency-dependent data through the fast Fourier transform. In order to respect the near-field approach, the arbitrary distance z₀ between the EM-field mapping plan and radiating source plan should be below one-sixth of the excitation signal minimal wavelength. In the second step, one applies the PWS transform to the obtained frequency-data. Then, through the Maxwell-Ampere relation, one can extract the E-field from the calculated PWS of the H-field. In the last step, the inverse fast Fourier transform of the obtained E-field gives the expected time-dependent results. The relevance of the proposed technique was confirmed by considering a set of five dipole sources placed arbitrarily in the horizontal plan equated by z = 0 and excited by a pulse current having amplitude of 50 mA and half-width of about 0.6 ns. As expected, by using the H_x, H_y and H_z 2-D data calculated with Matlab in the rectangular plan placed at z₀ = 3 mm and z₀ = 5 mm above the radiating source, it was demonstrated that with the proposed technique, one can determine the three components of the E-field E_x, E_y and E_z.

A novel approach for developing the electromagnetic fields from a lightning return stroke which follows a tortuous path will be presented. The proposed model is unique in that it recognizes that the symmetrical tortuosity of lightning directly impacts the observable distance r, which in turn, alters the resulting electromagnetic fields. In the literature, lightning return stroke models typically employ the assumption that the cloud-to-ground path is straight. Although this assumption yields fairly consistent results across an array of varying approaches, it does not account for lightning's natural physical appearance. Furthermore, straight-line models only account for the cloud-to-ground discharges and do not address branching and/or cloud-to-cloud discharges which are far more common. In reality, the ``steps'' which make up the lightning channel's initial descent are staggered or tortuous with respect to each other. Given this fact, the upward traveling current wavefront which follows this prescribed path will exhibit the same characteristics. In doing so, each current segment, which forms along its respective step, induces electromagnetic fields with angular aggregates that propagate outward from their origin. This, in turn, will generate spatial points where there are fields of higher and lower intensities. The results presented in this paper will show how the effective observable distance due to symmetrical tortuosity alters the resulting electromagnetic fields. Furthermore, it will be shown that as the observable distance r is increased, results from the proposed model closely resemble the straightline model which strongly suggests that symmetrical tortuosity is only influential at relatively close distances.

A wide band, integrated linear printed antenna array with low sidelobe cosecant square-shaped beam pattern is presented. Array synthesis mainly about the wide shaped coverage, low ripple and sidelobe level (SLL) has been done using the modified least square method by matrix inversion. A printed dipole integrated with wideband balun has been chosen as the array element for wide bandwidth and good integration with the feeding network. Simulated results have shown good agreement with the measured asured results of the antenna array, which has a VSWR≤1.3 bandwidth 15% and good pattern with cosecant square-shaped region beyond 30°and SLL≤−27 dB in L-band.

A planar hexa-band internal antenna designed for mobile phone applications is presented. The antenna occupying a small area of 45×12 mm² is placed on the top no-ground portion of the system circuit board with a ground-plane size of 45×100 mm². The design begins with constructing a meandered monopole. With a parasitic and an impedance-adjustment structure subsequently added, the resulting antenna can be viewed as a printed planar inverted-F antenna with a parasitic resonant element. Two wide impedance bands can be generated by the designed antenna to support GSM 850, GSM 900, DCS, PCS, UMTS, and 2.4-GHz WLAN operations. The measurement was found to agree reasonably well with the simulation. Design procedures and rules along with the design concepts behind are all presented in detail.

The level set algorithm is extended to handle the reconstruction of the shape and location of objects hidden behind a dielectric wall. The Green's function of stratified media is used to modify the method of moments and the surface integral equation forward solver. Due to the oscillatory nature of the Sommerfeld integrals, the stationary phase approximation is implemented here to achieve fast and accurate reconstruction results, especially when the targets are located adequately far from the wall. Transverse Magnetic (TM) plane waves are employed for excitation with limited view for transmitting and receiving the waves in the far field at one side of the wall. The results show the capability of the level set method for retrieving the shape and location of multiple 2D PEC objects of arbitrary shapes even when there are located at a small distance from the wall. To reduce the computational expenses of the algorithm in the case of multiple hidden objects, the MPI parallelization technique is implemented leading to a reduction in the CPU time from hours on a single processor to few minutes using 128 processors on the NCSA Supercomputer Center.

The Phase Angle Gradient Method (PAGM) is a recent technique developed for phase retrieval based on amplitude-only measurement data. Preliminary results have shown that the PAGM is able to perform phase retrieval at 100 MHz with accurate phase information based on measured field components on three planar surfaces. In this paper, a performance evaluation of the PAGM under different configurations is conducted. Phase retrieval based on field measurements for different plane sizes and separations between the planes are studied rigorously. In addition, the PAGM is tested for different initial phase distributions. The results show that the PAGM is capable of retrieving phase information even if the separation between the measurement planes is small in terms of wavelengths.

We develop a new adaptive inversion procedure: Data-adaptive Resolution Inversion (DRI) method, which eliminates the need of selecting a parameterization prior to inversion. Instead, one performs a hierarchical search for the correct parameterization while solving a sequence of inverse problems with an increasing dimension of parameterization. A parsimonious approach to inverse problems usually involves the application of the same refinement consistently over the complete spatial domain. Such an approach may lead to over-parameterization, subsequently, to unrealistic conductivity estimates and excessive computational work. With DRI, the new parameterization at an arbitrary stage of inversion sequence is allocated such that new degrees of freedom are not necessarily introduced all over the spatial domain of the problem. The aim is to allocate new degrees of freedom only where it is warranted by the available data. Inversion results confirm that DRI is robust and efficient for multiparameter inversion of multicomponent borehole electromagnetic measurements.

Short-wavelength radar networks are expected to complement current long-range weather radar systems. Accordingly, we proposed a configuration for such a network constituting pulse compression radars in order to use frequency resources efficiently and obtain multi-static information. We developed high resolution Ka-band pulse compression weather radar system as a test-bed. Using a commercial direct digital synthesizer (DDS) and field programmable gate array (FPGA) control, we generated linear and arbitrary nonlinear frequency modulated waveforms for low range sidelobes. Further, we completed a high duty factor system with a solid-state power amplifier. In a vertical-pointing mode, we were able to employ the developed radar to detect moderate rainfall up to 15 km. Details of the system design, hardware structure, data acquisition and processing algorithms were described. To validate the performance of the proposed radar system, we conducted several experiments by measuring cloud, snow and rain.

We numerically investigate the interaction of nonlinear pulses in coupled transmission lines with regularly spaced Schottky varactors. The c mode and π mode are two different propagation modes that can be developed on a coupled line. Recently, we have found that both modes can support soliton-like pulses due to the presence of the Schottky varactors and proposed a method of doubling repetition rate of the incident pulse stream. Through numerical evaluations, we find that small c-mode pulses are generated by colliding two π-mode pulses traveling in the opposite directions. Utilizing this unique property, the repetition rate of incident pulse stream can be increased by the factor greater than 2.

In this paper, single-crystalline silver filaments with periodic, pearl-chain-like structures are fabricated by electrodeposition without using any templates, surfactants, and additives. Simulations demonstrate that excited surface waves may sustain on silver pearl chains in middle infrared (Mid-IR) range. Based on the propagation features of surface waves on the silver filaments, this structure can be applied for electromagnetic wave transmittance in Mid-IR range. The propagation features of surface waves on the silver filaments indicate the structure application for Mid-IR wave transmittance.

A miniaturized internal wideband antenna suitable for integration with the printed circuit board (PCB) of a wireless universal serial bus (WUSB) dongle is presented in this paper. The proposed antenna mainly consists of a folded metal plate with two sides beveled. By introducing a short-circuited pin connected to the system ground and etching a pair of slots in the bevel sides of the folded metal plate, a large impedance bandwidth from 2.4 GHz to more than 11 GHz is obtained, which easily covers the 2.4 GHz WLAN, WiMAX, S-DMB and UWB frequency bands. The effects of the short-circuited pin and the narrow slots on the impedance matching of the proposed antenna are investigated. The proposed antenna is easy to be fabricated by bending a sample metal plate due to its miniaturized geometry of 5×12×12.5 mm³. Details of the antenna design are described, and experimental results of the constructed prototypes are presented and discussed.

A new model (EWGM) is presented to predict the resonant frequency of Rectangular Dielectric Resonator Antenna (RDRA) more accurately. Correction factors are introduced to calculate the effective dimensions by considering the effect of relative permittivity and aspect ratios (length/height and width/height) of RDRA. Results obtained from EWGM are compared with previous studies and experimental data to show its accuracy and effectiveness.

A fractal array is an antenna array which holds a property called "self-similarity". This means that parts of the whole structure are similar to the whole. A recursive procedure for evaluating the impedance matrix is allowed primarily by exploiting the self-similarity. However, numerous fractal arrays are extremely complicated in structure. Therefore, for these arrays, it is extremely elaborate to formulate explicitly a recursive relation. This paper proposes a simple procedure for evaluating, without formulating explicitly a recursive relation, the impedance matrix of fractal and fractile arrays; a fractile array is any array with a fractal boundary contour that tiles the plane without gaps or overlaps.

Non Destructive Testing techniques are more and more exploited in order to quickly and cheaply recognize flaws into the inspected materials, specially for carbon fiber reinforced polymers in recent years. Their production which are widely used both in civil and military applications, is an elaborate process un-free from faults and problems. Problems during the manufacturing, such as plies' overlapping, can cause flaws in the resulting material, this way compromising its integrity. Within this framework, this work aims to propose a design of ferrite core probe for eddy current non destructive evaluation, in order to investigate the presence of defects in carbon fiber epoxy composite materials. In this context, modelling is a powerful tool for inspection improvements. It helps probe-coil designers to optimize sensors for each examination requirement, providing better understanding of the involved physics, supporting operator training and increasing defect analysis reliability. Particularly, Finite Element based analyzes will be carried out into this path. After this step, in order to improve the quality of simulated measurement, a filtering technique has been exploited in order to improve the accuracy and performance of the flaw detection.

We have derived a one-variable metric function for fast and accurate complex permittivity extraction of low-to-high-loss materials using reflection-only microwave non-resonant measurements at one frequency. The metric function can be modified to facilitate fast computation of the complex permittivity of materials for various applications (e.g., relative complex permittivity measurement of low-loss materials). It is useful as a measurement tool for broadband measurements of complex permittivity of samples with substantiate lengths. In addition, the method is applicable for measurement of complex permittivity of dispersive materials or complex permittivity of non-dispersive samples in limited frequency-band applications, since it is based on point-by-point (or frequency-byfrequency) extraction. It is validated by a numerical analysis and measurements of a liquid sample.

The nonlinear responses of a one-dimensional heterostructure containing two kinds of single-negative materials with an air gap are investigated. It is shown that the frequency of zero-phase gap bistable heterostructure can be tuned simply by adjusting the width of air gap. On the other hand, the optical bistability is achieved at very low values of input intensity due to the enhancement of Kerr nonlinearity near the frequency of the defect mode. It is shown that transmission of the structure is relatively insensitive to incident angle and losses.

A novel dual-wideband printed monopole antenna is proposed for wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX) applications. The proposed antenna consists of a T-shaped monopole on top and dual combined G-shaped slots located symmetrically on the ground plane to achieve a dual-wideband performance. Prototype of the proposed antenna has been constructed and tested. The measured 10 dB bandwidths for return loss are 1.76 GHz from 2.13 to 3.89 GHz and 0.92 GHz from 5.03 to 5.95 GHz, covering all the 2.4/5.2/5.8 GHz WLAN and 2.5/3.5/5.5 GHz WiMAX bands. And this antenna also has omni-directional patterns over the lower operating range.