In this article we developed a new method of calculation of the active microwaves circuits in micro ribbon technology. This technique is based on the iterative method where localised auxiliary sources are introduced to model the active elements of the circuit (ultra high frequency diodes). To validate this work, the results obtained are compared with those obtained by the software momentum of advanced design system (ADS). We show primarily the interests and the operational limits of auxiliary source in the formulation of the considered problem.

Ultra-Wideband (UWB) radar is one of the most promising emerging technologies for the early detection of breast cancer, and the development of robust beamforming algorithms for imaging has been the subject of a significant amount of research. Extending the monostatic Microwave Imaging via Space Time (MIST) beamformer originally developed by Bond et al., the authors proposed the Multistatic MIST beamforming algorithm that uses the spatial diversity of the receiving antennas to acquire more energy reflected from dielectric scatterers which propagate outwards via different routes, while compensating for multistatic path-dependent attenuation and phase effects. In this paper, the performance and robustness of the Multistatic MIST beamformer is examined across a range of potential clinical scenarios. The multistatic beamformer is directly compared with the traditional monostatic beamformer and the effects of the additional multistatic channels is investigated. Furthermore, the robustness of the beamformer with respect to tumor size and location, variations in dielectric properties, and significantly, different fibroglandular tissue distributions within the breast based on recently published data, is examined.

A comparative analysis of transmit diversity and beamforming for linear and circular antenna arrays in a wireless communications system is presented. The objective is to examine the effect of random perturbations, angular power distributions on transmit diversity and beamforming system. The perturbations are modeled as additive random errors, following complex Gaussian multivariate distribution, to the antenna array steering vectors. Using outage probability, probability of error, and dynamic range of transmitter power as performance measures, we have shown significant effects of array perturbations on the two systems under spatially correlated Rayleigh fading channel. We also examine the effect of angular power distributions (uniform, truncated Gaussian, and truncated Laplacian), which corresponds to different propagation scenario, on the performance of the two systems. Results show that the central angle-of-arrival can have significant impact on system performance. And the transmit diversity system with truncated Laplacian distribution performs better as compared to other power distributions, and linear array is a preferable configuration for transmit diversity system. We conclude that array perturbations must not be neglected in the design of transmit diversity and beamforming systems.

A compact single-feed dual-band circularly polarized (CP) microstrip antenna is evaluated numerically and experimentally. The dual-band performances with small frequency ratio (about 1:1.1) are achieved by a circular patch and a narrow annular-ring, which have small difference in radius. The CP characteristics are achieved by an unequal cross-slot embedded in the circular patch and two orthogonal linear stubs spurred from the annular-ring. The antenna is easy to fabricate. Good agreement is obtained between measured and simulated results.

In this paper, a miniaturized bandpass filter with controllable harmonic by using split impedance resonators is proposed. The proposed split impedance resonator is based on the theories of the basic parallel impedance formula and stepped impedance resonators (SIRs). In this way, the split impedance resonator can be effectively designed to obtain good coupling for reducing the insertion loss. Furthermore, a miniaturized bandpass filter with controllable spurious frequency is proposed. The proposed bandpass filter not only has good passband characteristics but also obtains miniaturization around 21.87% versus the traditional SIR bandpass filters.

ƒAn improved finite difference time domain (FDTD) method is employed for fast capturing transient responses of reconfigurable and multiple-input-multiple-output (MIMO) antennas under the impact of an intentional high-power electromagnetic pulse (EMP) but with different waveforms, respectively, where lumped element and sub-cellular thin-wire algorithms and coaxial feed model are integrated together for handling such three-dimensional antennas used for wireless communication. Parametric studies are carried out to show effects of high-power EMP waveforms, its polarization state and incident direction on the transient coupled voltages on the coaxial feed line and across the diodes, with sufficient information obtained for understanding the interaction between the EMP and the antennas.

Reliable performance of a component or structure depends on its pre-service quality and in-service degradation under operating conditions. The importance of Non-Destructive Testing and Evaluation is ever increasing, above all in ensuring pre-service quality and monitoring in-service degradation, in order to avoid premature failure of the components/structures. There are many Non-Destructive Techniques based on various physical principles. In this work, our main objective is the characterization of anomalies such as defects, stresses and microstructural degradations in materials. Particularly, in this work we propose a Finite Element Method based approach for modelling a fast and accurate evaluation of defects in metallic materials able to easily detect defects, aside from the orientation. Within this framework, the paper proposes the application of a magnetic field rotating perpendicularly to the analysed specimen. We discuss a few case studies, starting from numerical simulations and finally highlighting the importance of this approach in order to evaluate the structural integrity assessment.

A shielded, conductor-backed coplanar waveguide technique is used to determine the complex permittivity and loss tangent of nano magnetic composite materials over X-band. The test composite material is synthesized by reinforcing cobalt ferrite particles with average crystallite diameter 7.36nm in low density polyethylene matrix with 2% and 4% volume fractions. The complex permittivity for low density polyethylene matrix and the composite samples, evaluated from the present technique at 9.887 GHz, are verified with cavity perturbation technique resonating at the same frequency. A new mathematical approach, using element-to-element correspondence of the ABCD matrix, is applied to calculate the complex propagation constant. The formulation facilitates evaluation of complex propagation constant over the test frequency range using scalar scattering parameters without altering the coplanar waveguide geometry. The mathematical formulation is verified by performing permittivity measurements for air over the X-band.

Multilayered structures consisting of alternating negative-permittivity and dielectric layers are explored to obtain high-resolution imaging of subwavelength objects. The peaks with the smallest |k_y| (k_y is the transverse wave vector) on the transmission curves, which come from the guided modes of the multilayered structures, can not be completely damped by material loss. This makes the amplitudes of the evanescent waves around these peaks inappropriate after transmitted through the imaging structures, and the imaging quality is not good. To solve such a problem, the permittivity of the dielectric layers is appropriately chosen to make these sharp peaks merge with their neighboring peaks, whose corresponding guiding modes in the multilayered structure are cutoff. Wide flat upheavals are then generated on the transmission curves so that evanescent waves in a large range are transmitted through the structures with appropriate amplitudes. In addition, it is found that the sharp peaks with the smallest |k_y| can be eliminated by adding appropriate coating layers and wide flat upheavals can also be obtained.

This work presents a new technique that uses floating plate overlays to realize the open-loop resonator bandpass filter with characteristics of compact size and having four controllable transmission zeros to achieve the multispurious suppression. Three floating plate overlays are used to cover parts of the open-loop resonator filter to increase the coupling between resonators and move the transmission zeros to desired frequencies to enhance harmonic suppression. A design procedure that developed based on an equivalent circuit model of such a new type of filter is proposed. Two experimental prototypes are designed and fabricated to verify the proposed design method. The measured results agree well with the simulations. The measured insertion losses of the prototypes in passband are all less than 2 dB. One prototype is designed to suppress third, fourth, and fifth harmonics with the suppression greater than 30 dBc. Another prototype can suppress second, third, and fourth order harmonics below 20 dBc. In addition, prototype circuit areas are only about 50 percent of the conventional open-loop filter.

This paper investigates an H-fractal wideband microstrip filter with multi-passbands and a tuned notch band for wireless communication frequencies. The four different filter configurations explored are: symmetric with zero offset, symmetric with nonzero offset, asymmetric with zero offset, and asymmetric with nonzero offset. The effect of H-fractal iterations, fractal scaling parameters, and stub offset on the filter's multi-passband response is presented. A comparison is made to a non-fractal straight stub filter of equivalent length showing improved passband bandwidth while maintaining the same overall response. Then an asymmetry is introduced into the fractal geometry to produce a tuned notch band in the second passband. Two fractal scaling factors are shown to aid in the tuning of the filter notch band. Finally, an asymmetric filter is fabricated on FR-4 substrate and experimentally verified, illustrating that the filter has multi-passbands and can find applications in WiFi/WiMAX transponders. The fabricated filter's first two passbands (with respect to S₁₁ = -10 dB) are: from 2.09 GHz to 3.18 GHz (fractional bandwidth of 1.09 GHz, 41.36%) and from 4.1 GHz to 5.43 GHz (factional bandwidth of 1.33 GHz, 27.91%), both for WiFi applications along with a notch band (S₂₁ = -3 dB) from 3.3 GHz to 3.94 GHz (factional bandwidth of 0.64 GHz, 17.67%) to suppress co-site WiMAX transmission. The measured data agrees reasonably well with the simulated filter response.

A simplified extended composite right/left-handed (SE-CRLH) transmission line (TL) is proposed for dual-band applications. The dual-band bandpass behavior is realized with a simplified non-dual circuit with only two broadband balanced conditions. The dispersion relation and frequency response of SE-CRLH TL are analyzed by circuit analysis, Bloch-Floquet theorem, and full wave simulation. A demonstration of SE-CRLH structure is designed. The measurements are in agreement with simulations and theory.

In this paper, a new N-way multi-frequency unequal split Wilkinson power divider (WPD) is proposed. The dividers are composed of multi-section transmission line transformers (TLT) and isolation resistors, which provide high isolation and very good input/output ports matching simultaneously at arbitrary design frequencies. To verify the validity of the design, several multi-frequency power dividers are designed and simulated. Specifically, a 3-way unequal split dual-frequency WPD operating at 900 and 1800 MHz, a 3-way unequal split triple-frequency WPD operating at 1, 2, 3 GHz, and a 4-way equal split quad-frequency WPD operating at 1, 2, 3, 4 GHz, are designed.

Frequency shift of the spectrum of an incident optical pulse by an intense THz pulse inducing cross-phase modulation (XPM) in a nonlinear dielectric slab is analyzed. The effect is predicted with a high degree of accuracy using the well-known transmission line matrix (TLM) technique. In this research, to model the THzinduced temporal and spatial variation of the dielectric permittivity of the nonlinear dielectric slab, the transmission lines of the TLM method are loaded with open shunt stubs. The parameters of the stubs are modified in accordance with the refractive index variation of the dielectric slab, here ZnTe, induced by the strong THz pulse. The obtained numerical results are verified with a recently reported experimental work.

A recently presented equivalent conductor (EC) method enables fast computation for the radar cross section (RCS) of a chaff cloud. Despite its good performance, the EC method is restrictively applicable due to the complex orientation distribution of chaff and the incident angle. In this paper, a generalized equivalent conductor (GEC) method is presented for estimating the RCS of an actual chaff cloud. The proposed method can be applied to any orientation distribution of the chaff cloud by using a weight function and a weighted average, as well as to any incident angle by employing a method of moment (MoM). Numerical results are presented for three scenarios and validated with results of the MoM.

A new method is presented for analysis of transient electromagnetic fields in regular structures with abrupt discontinuities. The method is based on mode expansion of the fields in the Time Domain. The modes propagate independently in the regular parts of the structure and are coupled at the discontinuity. The main idea consists in solving 1D FDTD equations for each independent mode channel in the regular waveguides and using mode-matching at the junction cross-section in order to relate the mode amplitudes in all the channels at the same time instant via imposing boundary conditions. As examples the problems of pulse signal diffraction at a step discontinuity in a parallel-plate waveguide, diffraction at a junction of circular and coaxial waveguides, and pulse radiation of a bi-conical antenna are considered. The latter problem is treated as a junction of two conical lines (one of which is the free space) that are regular in spherical coordinates.

In this paper, a large number of studies of the effect of the foliage on single or lines of trees on modern wireless communication systems are reviewed. The paper is focused on the experimental works mainly done for commercial applications such as cellular communication and high speed point-to-point fixed link at the microwave and millimeter wave frequencies. For this review study, the development of the foliage loss prediction methods and the factors influencing the tree-induced shadowing effect are highlighted. In view of current research work in this area, some possible future works are proposed to improve the performance of modern wireless communication systems with the effect of foliage.

Adaptive Neuro-fuzzy systems constitute an intelligent systems hybrid technique that combines fuzzy logic with neural networks in order to have better results. A study is presented to forecast the relative magnetic permeability using ANFIS. The global electromagnetic parameter, namely, the magnetic induction has been used as input to estimate the relative magnetic permeability. In this exceptional research, finite element simulations are carried out to build up a database which will be used to train ANFIS network. The ANFIS approach learns the rules and membership functions from training data. The hybrid system is tested by the use of the validation data. Performance of the trained ANFIS network was compared with the multilayer feed forward network model and experimental results. The results show the effectiveness of the proposed approach in solving inverse electromagnetic problem.

In this paper a multifunctional microstrip antenna is designed, fabricated and experimentally verified for operation in AWS, GSM, WiMAX and WLAN bands. This microstrip patch antenna has two U-shaped slots to achieve the dual wideband operation required to meet these specifications. The dimensions and locations of the U-slots are designed appropriately. The thick substrate used here helps in integrating the antenna with the existing aircraft panel material while achieving wide bandwidths. Experimental results of this single feed antenna indicate that it meets all current requirements for in-cabin wireless communication needs.

A capacitive method for measuring hand grip position on a mobile phone equipped with a dual-band planar inverted-F antenna (PIFA) and a monopole antenna was studied using different electrode arrangements. A capacitive sensor with a dual-electrode configuration and an antenna-integrated capacitive sensor for hand grip recognition were developed. The sensitivities of the sensors were measured along the front, side and back of the phone. The dual-electrode sensor configuration exhibited its best sensitivity of 29 fF at the bottom end of the phone. The PIFA antenna-integrated sensor proved to have sensitivity of 420 fF and the monopole antenna-integrated sensor had sensitivity of 115 fF, making them both reasonable solutions for hand grip sensors in mobile applications.