The influences of confined phonons on the nonlinear absorption coefficient (NAC) by a strong electromagnetic wave for the case of electron-optical phonon scattering in doped superlattices (DSLs) are theoretically studied by using the quantum transport equation for electrons. The dependence of NAC on the energy (hΩ), the amplitude (E₀) of external strong electromagnetic wave, the temperature (T) of the system, is obtained. Two cases for the absorption: Close to the absorption threshold ∣khΩ - hω₀∣<< ε and far away from the absorption threshold ∣khΩ - hω₀∣>> ε (k = 0, 1, 2..., hω₀ and ε are the frequency of optical phonon and the average energy of electrons, respectively) are considered. The formula of the NAC contains a quantum number m characterizing confined phonons. The analytic expressions are numerically evaluated, plotted and discussed for a specific of the n-GaAs/p-GaAs DSLs. The computations show that the spectrums of the NAC in case of confined phonon are much different from they are in case of un-confined phonon and strongly depend on a quantum number m characterizing confinement phonon.

In this paper, right handed circular polarization (RHCP), left handed circular polarization (LHCP), and linear polarization (LP) reconfigurable antenna is proposed by reconfigured fabrication. The proposed antenna comprising of two square patches, a T-stripline, and a finite ground plane is designed for HiperLAN2 5 GHz operation. The patches are symmetrically placed along the vertical portion of T-strip and coupling fed by the strip. The planar structure is in LP sense while CP sense is achieved as the structure bent. For the bent structure, the vertical and horizontal portions of T-strip not only respectively feed the coplanar patch but also provide a 90° phase difference between the feeds. Two orthogonal E-fields with quadrature are excited to achieve CP sense. Moreover, the switching between RHCP and LHCP is easily achieved by folding the structure along opposite vertical edge of T-strip. Instead of electrically controlling switches, the polarization reconfiguration can be manually constructed.

Silicon nitride (Si₃N₄) ceramic is a promising ultra-high speed (> 5 mach) broadband (1-18 GHz) radome material because of its excellent high-temperature resistance, good mechanical and dielectric properties. Si₃N₄ ceramics with A-sandwich wall structure are successfully applied to passive self-direction high transmission efficiency broadband radome (1-18 GHz). In the present study, a novel graded porous wall structure for broadband radome is promoted. The feasibility of using this structure is carried out by a computer aided design for the wall structure based on the microwave equivalent network method. By optimizing the layer number (n), structural coefficient (p), thickness (d) and dielectric constant (ε) of each layer, the power transmission efficiency at 1-18 GHz of graded porous Si₃N₄ ceramic radome is calculated. Si₃N₄ ceramics with graded porous structure are then prepared according to the design. The prepared sample exhibits a good graded porous structure with the porosity range from ~ 2% to 63%. The tested power transmission efficiency at 1-18 GHz for the obtained sample matches well with the calculation results, indicating that the graded porous structure is feasible for the broadband radome application.

In this paper, we present a tri-band filter design using tri-mode T-shaped branches connected by λ/4 transmission lines. By analyzing the input admittance of a T-shape branch with commensurate electrical lengths, three resonant modes with two transmission zeros between are found and design formulas are derived. The filter can be regarded as a combination of three bandpass filters with only one set of coupling elements. To realize different bandwidths for each, the admittance slope of each resonating mode is set as required. A genetic algorithm is used in solving related equations to obtain the impedance of each line in a T-shape branch, followed by a final optimization. A three-pole tri-band filter having passbands of 0.6-0.9, 1.35-1.65 and 2.1-2.4 GHz, is designed, fabricated and measured with low passband insertion losses of < 0.7 dB and high rejection of > 60 dB between the passband regions. As a generalization, necessary to achieve a tri-band filter with arbitrary passbands, a non-commensurate version of the T-shape branch is introduced. An example filter design is given with the passbands asymmetrically located at 0.7-1, 1.65-1.95, and 2.2-2.3 GHz. This technique is able to achieve good design flexibility with respect to bandwidth ratios. This is validated by studying the maximum impedance variations of a T-shape branch when the bandwidth ratios vary.

In this paper, we study tunable metamaterial structures whose unit cell has triangular split ring resonator and wire strip for S- and C-microwave bands. Three types of new metamaterials, concentric and non-concentric configurations, are designed, and their electromagnetic response is investigated. Constitutive and S parameters are computed using retrieval algorithm to demonstrate the properties of the proposed new metamaterial designs. In addition, the electric field distribution on the metallic parts of the structure is illustrated for one design of the each sample. It is shown that the studied new metamaterials exhibit double negative properties in the frequency region of interest. The main advantage of this study based on the proposed structures is having the tunability in terms of the substrate thickness and the possibility of pronounce loss reduction.

Frequency-dependent energy tunneling that results in full transmission of electromagnetic energy through wire-loaded sharp waveguide bends is demonstrated by full-wave simulations. The frequencies at which the tunneling takes place is predicted by a numerical method that involves a variational impedance formula based on Green function of a probe-excited parallel plate waveguide. Analogous tunneling effects have also been previously observed in waveguide bends filled with epsilon-near-zero media. However, since the frequency response in the wire-loaded waveguides can be tailored by simply modifying the lengths of the wires, the phenomenon is scalable over a broad range of frequencies and can be potentially exploited in various filtering and multiplexing applications.

This letter reports a new technique that enables simultaneous detection of concentrations of the organic and inorganic substances in a hybrid fluidic solution. The technique is based on a coplanar microwave distributed MEMS transmission line. Measurement results show that a hybrid aqueous solution with a mixture of 0 M -- 0.2 M NaCl and 0 mg/ml -- 350 mg/ml glucose can be easily detected simultaneously from measured one-port scattering parameter (S₁₁).

Abstract－This work presents a novel broadband monopole antenna for digital video broadcasting-terrestrial (DVB-T) application. The proposed antenna consists of a multiple-ring radiating patch and a sleeve-shaped ground plane. The multiple-ring monopole is used to realize the antenna height reduction at a fixed operating frequency. It shows a wide operating 2.5:1 VSWR bandwidth of 408 MHz achieved by using an impedance-matching technique. The technique applies cutting a notch at the ground plane opposite to the microstrip line and adjusting the height of the sleeve-shaped ground. The proposed antenna can operate in the 463-871 MHz frequency range and cover the DVB-T operating bandwidth (470-862 MHz). The radiation pattern of the proposed antenna in the xy-plane is omni-directional with a peak antenna gain of 4.2 dBi.

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.