A specialized type of traveling-wave field-effect transistor (TWFET), the gate and drain lines of which contain series capacitors, series inductors, shunt capacitors, and shunt inductors, is considered to provide a platform to manage unattenuated dispersion-free envelope pulses. Because of the nonlinearity caused by the gate-source Schottky capacitance, the dispersive distortion is well compensated. Moreover, the FET gain can cancel the wave attenuation caused by electrode losses. This paper discusses the design criteria of a TWFET using the nonlinear Schrodinger equation obtained by perturbation. Several numerical calculations follow to validate it.

A delay nonlinear differential equation is proposed to investigate the condition of the microwave chaotic behavior existing between the antenna and the front-end protection circuit of a receiver such as the radar front-end limiter circuit. This investigation concerns the case of intentional or unintentional signals applied to the antenna outside of its bandwidth. Bifurcation diagrams show that the chaotic behavior appears for antenna impedance up to 10 Ω and for amplitudes greater than 1.2 V. Electrical simulation results agree well with theoretical ones.

Recently, substrate integrated waveguide (SIW) technology attracts more and more attentions in the development of millimeter-wave integrated beamforming network (BFN) depending on its inherent advantages. However, the SIW-based BFN usually has a relative large circuit size. To overcome this weakness, we propose a novel multi-folded SIW Butler matrix at the center frequency of 60 GHz. Such a structure can reduce the circuit area more than 75% compared with the conventional single-layer version. Two different full-wave simulation tools are employed to validate our design. This folded BFN offers a number of benefits, such as highly compact configuration, low couplings between adjacent paths, and wide operation bandwidth. For convenient use, the SIW ports can be converted to the microstrip line ports arranged in order through a special broad-band two-layer transition network. Such a miniaturized SIW Butler matrix presents an excellent candidate in the development of compact intelligent millimeter-wave communication system.

We present a rigorous full wave calculation of the optical force on a dielectric cylindrical particle of an arbitrary size under the illumination of one dimensional (1D) Airy beam. The radiation force is written in terms of the cylindrical partial wave expansion coefficients of the non-paraxial 1D Airy beams. Our simulation results demonstrate that an Airy beam can accelerate the microparticles along its parabolic trajectory, while transverse to which the particles are trapped at the center of its main lobe, corroborating the possibility of the long distance particle transport by means of an Airy beam.

Millimeter waves can be used to detect concealed objects because they can penetrate clothing. Therefore, millimeter wave imaging draws increasing attention in security applications for the detection of objects under clothing. In such applications, it is critical to estimate the distances from objects concealed in open spaces. In this paper, we develop a segmentation-based stereo-matching method based on passive millimeter wave imaging to estimate the longitudinal distance from a concealed object. In this method, the concealed object area is segmented and extracted by a k-means algorithm with splitting initialization, which provides an iterative solution for unsupervised learning. The distance from a concealed object is estimated on the basis of discrepancy between corresponding centers of the segmented objects in the image pair. The conventional stereo-matching equation is modied according to the scanning properties of the passive millimeter wave imaging system. We experimentally demonstrate that the proposed method can accurately estimate distances from concealed objects.

In this paper we describe the realization of a low cost radiometer which can be used to detect and show the microwave electromagnetic field emitted from human body. The system uses components available in the consumer market: low cost LNB (Low Noise Block: low noise pre-amplifier, mixer and post-amplifiers) and a parabolic antenna for satellite TV. The base line stability problems of the system are removed using a detector in linear region and a digital integrator for correction of the base line. The PC resident software triggers an educational video on the origins of electromagnetic radiation when a person, entering in the antenna beam, is detected; in addition to this, it is possible to show an infrared image taken by a camera.

This article proposes a novel 4-sector cylindrical-rectangular microstrip array with high-gain operation and multi-beam radiation for IEEE 802.11j MIMO WLAN system. With the use of 1 x 2 array, the impedance bandwidth for the operating band of 5 GHz can reach about 2.5% (125 MHz), which is enough for IEEE 802.11j specifications. Peak antenna gains across the operating band are close to 11.0 dBi with the gain variations of 0.3 dBi.

Reflection from a perfect electric conductor (PEC) plane of infinite dimensions embedded in a second order nonlinear medium is studied. The reflected wave has two parts, one due to linear behavior, the other due to nonlinear behavior of the medium. The expressions of the reflection coefficients for parallel and perpendicular polarization cases are obtained. The reduction of reflection coefficient to a linear medium case is also reported. Dependence of the said coefficients on incident electric field intensity and the angle of incidence is also plotted.

New methods are presented for increasing the bandwidth of wire antennas using impedance loading. This paper extends the seminal Wu-King theory of the internal impedance profile that produces travellingwave only current modes on a center-fed dipole antenna. It also presents a numerical optimization methodology based on Central Force Optimization, a new deterministic multidimensional search and optimization metaheuristic useful for problems in applied electromagnetics. A CFOoptimized loaded monopole antenna is described in detail and compared to the same structure loaded with a fractional Wu-King profile. The CFO monopole generally performs better than other designs using either the full or fractional Wu-King profiles or the extended Wu-King profiles. The methods described in this paper should be useful in any wire antenna design that utilizes impedance loading to increase bandwidth.

A compact ultra-wideband (UWB) bandpass filter (BPF) with improved harmonic suppression using a modified coupling structure is presented in this paper. The modified coupling structure is constructed by taper-connecting two folded open stubs to the traditional parallel-coupled lines, which shows an improved characteristic in harmonic suppression. By integrating the proposed coupling and the stepped-impedance stub loaded resonator (SISLR), a UWB BPF is finally built and tested. The simulated and measured results are in good agreement with each other, exhibiting good wideband filtering characteristic and improved out-of-band performance.

This paper presents the design, simulation and measurement of a dual-band terahertz metamaterial absorber with polarization-insensitivity and wide incident angle. The unit cell of the metamaterial consists of top resonator structures and low metallic ground plane, separated by an isolation material spacer to realize both electric and magnetic resonances. The physical mechanism of dual-band absorption and the sensitivity to the polarization direction and incident direction of the EM wave are theoretically investigated by simulating the x-component and normal component electric field distribution, current distribution on ERRs and metallic ground plane, and distribution of power flow and loss at the resonance frequencies as well as different modes EM waves, based the FDTD calculated method, respectively. The results show that the absorber is not only correctly coupling to the incident electric field and magnetic field, but also can trap the input power into specific positions of the devices and absorb it, besides insensitive to the polarized angle and incident angle. Moreover, the experiment demonstrates that the absorber achieves two strong absorptions of 82.8% and 86.8% near 1.724 and 3.557THz.

Recent studies on artificial materials demonstrate that substantial improvements in electromagnetic response can be attained by combining different materials subject to desired metrics. However, the perfect material combination is unique and extremely difficult to determine without automated synthesis schemes. In this paper, we develop a versatile approach to design the microstructure of periodic materials with prescribed dielectric and magnetic material tensors. The proposed framework is based on a robust material model and generalized inverse synthesis tool relying on topology optimization. The former is derived using homogenization theory and asymptotic expansion applied to Maxwell equations and can characterize the effects of anisotropy and loss of materials with periodic unit cells of arbitrary geometries and multi-phases much smaller than the wavelength. Resulting Partial Differential Equation (PDE) is solved numerically using Finite Element Analysis (FEA) and is validated with results in literature. The material model proves to be fast and numerically stable even with complex inclusions. The topology optimization problem is applied for the first time towards designing the unit cell topology of periodic electromagnetic materials from scratch with desired dielectric and magnetic tensors using off-the-shelf materials, i.e., readily available constituents obtained from isotropic ceramic powders. The proposed framework's capability is demonstrated with five design examples. Design with anisotropic permittivity is also fabricated. Results show that the framework is capable of designing, in an automated fashion, non-intuitive material compositions from scratch with desired electromagnetic properties.

The specific absorption rate (SAR) of a human body exposed to a random field inside a reverberation chamber (RC) has been modeled. The exciting field is simulated using the plane wave integral representation which is numerically solved by a superposition of N plane waves randomly generated and repeated M times to reproduce the same statistics of an RC. An experimental validation, carried out by means of known saline solutions, confirms the reliability of this method. The obtained results at various frequencies for the adopted "Visible Human Body" and for some tissues well highlight the absorption percentage. The frequency behavior of the total SAR reveals the resonance of the human body around 75 MHz, in spite of the chaotic source.

A novel compact design of planar T-shaped monopole antenna with multi-band operation for WLAN/WiMAX system is proposed. By insetting a pair of mirrored L-shaped monopole strips, multi resonant modes close to 2.45/3.5/5.5 GHz band are excited to meet the specifications of WLAN/WiMAX system. And, the obtained impedance bandwidth across the operating bands can reach about 160/1100/2690 MHz for the 2.45/3.5/5.5 GHz bands, respectively. Only with the antenna size of 30×42×0.8 mm³, the proposed monopole antenna has the compact operation with more than 20% antenna size reduction. The measured peak gains and radiation efficiencies are about 3.2/3.5/5.4 dBi and 72/98/96% for the 2.45/3.5/5.5 GHz band, respectively, with nearly omni-directional pattern in the XY-plane.

The radio waves propagating through the earth atmosphere will be attenuated due to the presence of atmosphere particles, such as water vapor, water drops and the ice particles. Meanwhile, the atmospheric gases and rain will both absorb and scatter the radio waves, and consequently degrade the performance of the link. The results of various studies conducted in temperate and tropical regions have been published in research papers. This paper presents the summary of comparative studies on different rain attenuation prediction methods for terrestrial microwave links tropical regions. Basically the models described in this paper include those of the ITU-R, revised Moupfouma, revised Silva Mello and Lin model. The objective of this study is to reveal the most suitable rain attenuation prediction model for the Malaysian tropical region. This paper will provide useful information for microwave engineers and researchers in making decision over the choice of most suitable rain attenuation prediction for terrestrial links operating in a tropical region. Even though the ITU-R model underestimates the rain attenuation at higher frequencies, the test results have clearly indicated that it is most suitable for predicting terrestrial rain attenuation in tropical Malaysia, compared to others.

For array beampattern synthesis, it is possible to simplify the model and reduce the computational load by formulating it to be a Quadratic Programming (QP) problem. The QP method is conceptually simple and imposes no restriction on array geometry. In the QP method, a key component is the template function which describes the desired beampattern as a deterministic function of direction. In this paper, the template functions in the form of Hypergeometric Function corresponding to Legendre arrays and Dolph-Chebyshev arrays, namely Legendre Hypergeometric Function (LHF) and Dolph-Chebyshev Hypergeometric Function (DCHF), are derived and the synthesis procedures are also presented. The simulation results show that the DCHF and LHF work in the QP method and provide the exactly synthesized beampattern. Moreover, another synthesis method using a Gegenbauer polynomial to synthesize the beampattern of a Uniform Linear Array, is proposed. This method gives rise to the Gegenbauer arrays. Gegenbauer arrays are very generalized and Legendre arrays and Dolph-Chebyshev arrays are considered as its special cases. Using the Gegenbauer array synthesis method, one is able to further adjust the beam efficiency and the directivity when the Side-Lobe Level and the element number are specified. As well as Dolph-Chebyshev arrays and Legendre arrays, its template function for the QP method, Gegenbauer Hypergeometric Function, is also derived.

The berthing of large ships in inclement weather with frequently poor visibility presents a challenge. To assist with this application, it may be beneficial to utilise standard radar imaging. Whilst this may be achieved using a mechanically-scanned system, reliability, cost and weight issues, coupled with the need to primarily image only a 120º sector on the port and starboard of the ship, make phased array radar an attractive possibility. Multiple-Input Multiple-Output (MIMO) radar, with its ability to enhance the resolution available from a given number of elements, is particularly suited to a short-range application such as this in which there is sufficient time to switch between antenna elements as an alternative to more complex implementations. This paper describes a system of this nature from its basic architecture to development and validation, including some artefacts of the particular topology employed.

The magnetic properties of the metamaterial composed of both periodic and aperiodic closed rings are studied. Experimental results validate that metamaterials with 0 < μ < 1 can be non-dispersive in a wide frequency range. The magnetic properties are insensitive to disorders of the closed rings, e.g., the position disorders and the size disorders. The related causality issue is also discussed.

In this paper, a novel maximum likelihood algorithm for joint angle and delay estimation is developed to identify the specular components of channel fading for uniform linear array based on the physical propagation channel model. Frequency domain presmoothing is applied to the structured frequency transfer matrix before the estimation procedure in order to utilize substantial observations. Iterative Gauss-Newton method is used to solve the multidimensional optimization problem, and a new compact matrix form is presented. Further simplification of the iteration is derived based on the assumption of independent channel parameters. Both simulations and measurement results are investigated for performance analysis. The simulations reveal that the proposed algorithm leads to higher performance with appropriate complexity. Also, a comparison with other algorithms is carried out to validate the accuracy of algorithm by using the power delay profile measured in a real environment, and the results show the proposed algorithm performs well.

The goal of this work is to look for a technique of optimization making it possible to improve the optical performances of materials with photonic band gap by reducing of the Kiessig fringes. The techniques of apodization and smoothing were used. The combination of these two techniques made it possible to reduce the Kiessig fringes up to 95%.