Analytical expressions for the average intensity, mean-squared beam width and angular spread of partially coherent standard and elegant Laguerre-Gaussian (LG) beams propagating in turbulent atmosphere are derived. The properties of the average intensity, spreading and directionality of partially coherent standard and elegant LG beams in turbulent atmosphere are studied numerically and comparatively. It is found that the beam parameters and structure constant of turbulence together determine the properties of the beams in turbulent atmosphere. Partially coherent standard and elegant LG beams with smaller coherence length, larger beam orders and longer wavelength are less affected by the turbulence. A partially coherent elegant LG beam is less affected by turbulence than a partially coherent standard LG beam under the same condition. Furthermore, it is found that there exist equivalent partially coherent standard and elegant LG beams, equivalent fully coherent standard and elegant LG beams, equivalent Gaussian Schell-model beams that may have the same directionality as a fully coherent Gaussian beam both in free space and in turbulent atmosphere. Our results will be useful in long distance free-space optical communications.

This paper applies the recently introduced electrical engineering approach to investigate room temperature THz metal shielding, using the accurate classical relaxation-effect frequency dispersion model. It is shown that, with the simplest case of a uniform plane wave at normal incidence to an infinite single planar shield in air, all figure of merit parameters for the shield can be accurately characterized. The errors introduced by adopting the traditional and much simpler classical skin-effect model are also quantified. In addition, errors resulting from adopting well-established approximations have also been investigated and quantified. It is shown that the engineering approach allows analytical expressions to be greatly simplified and predictive equivalent transmission line models to be synthesized, to give a much deeper insight into the behaviour of room temperature THz metal shielding. For example, it is shown that figures of merit and associated errors (resulting from the use of different classical frequency dispersion models) become essentially thickness invariant when the physical thickness of the shield is greater than 3 normal skin depths.

An analytical approach is developed in the present paper to investigate the interaction between two non-magnetic particles migrating in a conductive fluid due to an imposed strong magnetic field (e.g., 10 Tesla). The interaction between the conductive fluid and a single particle migrating along the magnetic lines is influenced by the magnetic field and can be represented by an additional fluid viscosity. Thus the effective fluid viscosity is discussed and the magnetic field effect on the particle migrating velocity is examined. For two particles, two kinds of magnetic forces are induced: namely, the attractive force due to the magnetisation and the repulsive force caused by the conductive fluid flow around the non-magnetic particles. The forces are then evaluated with the consideration of the magnetic field effect on the particle migration and become significant with the increase of the magnetic flux density. The counteracting behavior with a critical particle size of the interparticle magnetic forces is discussed and compared with different magnetic field densities and gradient values.

A geometrically based channel model is proposed to describe radio propagation in an indoor environment with directional antennas. In conventional geometric channel models (GCMs), distribution of scatterers does not take into account the antenna properties. A different approach is taken here for directional channel modeling. The locations of scattering objects are defined using non-Cartesian coordinates comprising an auxiliary geometric parameter ρ and angle-of-arrival (AOA) φ. Subsequently, we present a systematic method to study the influence of antenna pattern on scatterer distribution by applying two heuristic rules, which underpin the connection between the physical wave-propagation process and its canonical GCM. Provided with model preliminaries, important channel parameters including power azimuthal spectrum (PAS), power delay spectrum (PDS), mean effective gain (MEG), and antenna-decoupled PAS are derived and compared against the published data in the existing literature to demonstrate the usefulness of the proposed model.

This paper presents a very flexible and generic design of a diode-based RF predistortion linearizer that can correct for the dual-inflection point type compression characteristics found in the gain profile of metal semiconductor field effect transistor (MESFET) based and Doherty power amplifiers. It consists of a circuit configuration that has the head-tail configuration of Schottky diodes, complemented with a p-intrinsic-n (PIN) diode in parallel, at two ports of a 90° hybrid coupler for improving the performance of the linearizer. The use of a PIN diode in the linearizer provides it with an extra level of freedom in achieving the desired characteristic. Overall, the linearizer is equipped with three degrees of freedom and hence possesses the capability to achieve output characteristics that can be employed in linearizing various types of power amplifiers. The proposed linearizer has been shown to simultaneously improve the third- and fifth-order intermodulation distortions of a commercial ZHL-4240 gallium arsenide field effect transistor (GaAs FET) based power amplifier over a 10 dB power range.

In order to improve measurement efficiency in electromagnetic test facilities (compact range or near-field range), testing probes are required to have ultra-wideband (UWB) radiation characteristics, dual-polarization capability, and interchangeable E- and H-plane far-field patterns. In this context, we propose a new type of UWB antenna that satisfies these requirements in the frequency range of 4 to 18 GHz. For the proposed antenna, a low-loss dielectric material is loaded over pairs of balanced feeds to overcome radiation performance degradation addressed in purely metallic antennas. Also, radiation patterns are further improved by employing a lens aperture and shielding structures. The measured results of the final antenna design demonstrate broad and stable far-field patterns (half-power beamwidth > 45^◦), low voltage standing-wave ratio (< 2), similar E- and H-plane patterns, and large cross-polarization isolation (> 23 dB).

The programmable graphics processing unit (GPU) is employed to accelerate the unconditionally stable Crank-Nicolson finite-difference time-domain (CN-FDTD) method for the analysis of microwave circuits. In order to efficiently solve the linear system from the CN-FDTD method at each time step, both the sparse matrix vector product (SMVP) and the arithmetic operations on vectors in the bi-conjugate gradient stabilized (Bi-CGSTAB) algorithm are performed with multiple processors of the GPU. Therefore, the GPU based BI-CGSTAB algorithm can significantly speed up the CN-FDTD simulation due to parallel computing capability of modern GPUs. Numerical results demonstrate that this method is very effective and a speedup factor of 10 can be achieved.

The primary requirement for maximum power transfer and minimum power loss is matched impedance in a transmission system. However, static design variations in system such as parasitics and dynamic variations such as changes in transmission frequency will result in reflections. A redesign or reconfiguration of complex systems is neither easy nor cost effective. A noble technique for compensating reflections in a communication system is presented here. The proposed methodology adapts the system to change without any modification to the system physical configuration. In this methodology compensation signals are added by I/O drivers with programmable phase delay and drive strength adjustments to cancel reflections. The concept application is demonstrated for a narrow bandwidth antenna system. An operating frequency off the antenna frequency results in a degraded received message eye. Using the proposed technique, without modifying the antenna, reflections were compensated and a significantly improved data eye was produced, as measured by the enhancement of critical performance parameters. The architecture of an expanded driver to implement the concept is outlined here. An algorithm and flow chart to dynamically identify and compensate for reflections are also presented.

Three novel shapes of mushroom-like electromagnetic band-gap (EBG) structures are presented in this paper. The three shapes are based on rectangular metal strip with different combinations. The performances of the three-shape structures are studied by using both incident plane wave method and transmission coefficient approach. The effect of height and via location are also studied to achieve multi or wide band gap. These shapes are embedded in microstrip patch antenna substrate. The performance of the MPA is improved as increasing the antenna gain by 5 dBi, decreasing the surface current so improving the antenna radiation pattern as well as reducing the antenna size by more than 70% compared to the original size. The new shapes of EBG structure are integrated with MPA as a ground plane, where the conducting ground plane is replaced by a high impedance surface EBG layer. Parametric studies are conducted to maximize their impedance bandwidth and gain. It is found that the antenna bandwidth increased by about four times than original band and its gain is similarly increased. Sample of these antennas are fabricated and tested, to verify the designs.

Compact dual-band bandpass filter (BPF) with wide and narrow bands simultaneously is presented. By using the stepped impedance resonators (SIRs) in multilayered structure, the dual-band responses with wide and narrow bands simultaneously can be obtained. The filter has 3-dB fractional bandwidths (FBWs) of 45% and 10% for 2.4 GHz and 5.2 GHz, respectively. The circuit size is compact due to the multilayered structure. Moreover, multi-path propagation inside the multilayered structure generates transmission zeros at each skirt of the passbands for improving the passband selectivity. Measured results of the filter are in good agreement with the full-wave electromagnetic (EM) simulation.

The resonance frequency of Split-Ring Resonators (SRRs) loading a microstrip transmission line was tuned by means of a Ba_0.5Sr_0.5TiO₃ (BST) ferroelectric thin film. For a bias of 30 Volts, we obtained a band-stop response with a shift around 7% of the resonance to higher frequencies in Ku band. The originality of the device under test is (i) the utilisation of single C-shaped SRRs, (ii) the localisation via chemical etching of the BST film to voltage controlled interdigitated capacitances and (iii) the enhancement of the operating frequency (around 17 GHz).

We present exact three-dimensional semi-analytical expressions of the force exerted between two coaxial thick coils with rectangular cross-sections. Then, we present a semi-analytical formulation of their mutual inductance. For this purpose, we have to calculate six and seven integrations for calculating the force and the mutual inductance respectively. After mathematical manipulations, we can obtain semi-analytical formulations based on only two integrations. It is to be noted that such integrals can be evaluated numerically as they are smooth and derivable. Then, we compare our results with the filament and the finite element methods. All the results are in excellent agreement.

In this paper an inverse source problem is investigated. The measurement set-up is a reflector antenna covered by a radome. Equivalent currents are reconstructed on a surface shaped as the radome in order to diagnose the radome's interaction with the radiated field. To tackle this inverse source problem an analysis of a full-wave integral representation, with the equivalent currents as unknowns, is used. The extinction theorem and its associated integral equation ensure that the reconstructed currents represent sources within the radome. The axially symmetric experimental set-up reduces the computational complexity of the problem. The resulting linear system is inverted by using a singular value decomposition. We visualize how the presence of the radome alters the components of the equivalent currents. The method enables us to determine the phase shift of the field due to the transmission of the radome, i.e., the IPD (insertion phase delay). Also, disturbances due to defects, not observable in the measured near field, are localized in the equivalent currents.

A set of algorithms, specifically developed to facilitate an effective modeling of fractal-boundary microstrip antennas in the analysis of such structures through numerical electromagnetic (EM) solvers is presented in this paper. A fractal generator based on the implementation of an Iterated Function System (IFS) produces the geometry specified in accordance with the user-defined input parameters. The structure is created through a solver-specific interface and is thus applicable to a commercially available EM simulation suite. The generation of specific shapes through these algorithms provides a flexible method to study different geometries without the need to modify either the interface or the solver. Three structures based on the Minkowski fractal obtained through these techniques have been studied using two EM solvers for comparison. The frequency-domain results show good agreement between the two solvers, thus validating the algorithms implemented. Complex structures with higher iterations can be studied using these algorithms.

A model for two-dimensional layered medium is proposed for through-wall imaging problem. It is integrated with the subspace-based optimization method for reconstructing the relative permittivity profile in a fast and robust manner. Numerical results have shown that the concealed targets within walls can be reconstructed well using the proposed model even though full aperture of targets is not available due to the presence of walls. The model has also been employed for studying the effect of the presence of walls on imaging.

In this paper, we present a new dual band planar antenna. The proposed antenna consists of a microstrip patch with a U-shaped slot that is fed by a broadband electromagnetic coupling probe, known as L-probe. Radiation characteristics of the antenna and different methods for control of the resonant frequencies are investigated.

This paper presents microstrip array antenna integrated with novel shapes of 2D-electromagnetic band-gap structure (2D-EBG). Three different shapes of 2D EBG are used for harmonic suppression, optimizing the current distribution on the patches and decreasing the mutual coupling between array elements. As a result, the performance of the antenna array is improved. The three novel shapes of 2D-EBG presented are star, H shaped and I shaped slots. Simulated and measured results verify the improved performance of the array antenna compared to the antenna without EBG as well as antenna array with conventional EBG shapes. The harmonic suppression and reflection coefficients are improved by about 18 dB. Minimum mutual coupling is less than -20 dB, and the antenna size is reduced by 15% compared to the original size.

Two novel designs for compact reconfigurable antennas are introduced for wireless communication devices. These designs solve the steering frequency problem by tracking the desired resonance frequency or by generating various operating frequency bands to be selected electronically. In the first design, the length of the rectangular defected ground structure (RDGS) is electrically adjusted to change the resonant frequency of the MPA. While in the second design different turns of spiral AMC ground plane generate frequency bands, or modes, that are selected/optimized to serve different communication systems simultaneously. These systems may include various combinations of bluetooth, S-band and wireless local-area network (WLAN). These designs have several advantages as the total antenna volume can be reused, and therefore the overall antenna will be compact, although, the radiation of the MPA is kept fixed without any degradation. The designs are verified through both numerical simulations and measurement of a fabricated prototype. The results confirm good performance of the single and multiband reconfigurable antenna designs.

This paper studies optical solitons, in presence of higher order dispersion terms by the aid of He's semi-inverse variational principle. Both Kerr law and power law are taken into consideration. The numerical simulations are also given to complete the analysis.

Up to now, the terahertz (THz) band is still an unexplored region in the sense that no practical application exists. New operating principles by traveling wave concept should be, therefore, appreciated for the real applications. In this paper, the generalized three-dimensional (3D) transverse magnetic (TM) mode analysis to analyze the characteristics of two-dimensional electron gas (2DEG) drifting plasma at the III-V high-electron-mobility-transistor (HEMT) hetero-interface such as AlGaAs/GaAs hetero-interface and its interaction with propagating electromagnetic space harmonic wave is presented. It includes, (1) the determination of electromagnetic fields in semiconductor drifting plasma using the combination of well-known Maxwell's equations and carrier kinetic equation based on semiconductor fluid model and the derivation of the effective permittivity of drifting plasma in 2DEG on semi-insulating substrate, and (2) the analysis to describe the presence of interactions using a so-called interdigital-gated HEMT plasma wave devices. To describe the interaction, the admittance of the interdigital gate is evaluated. The numerical procedures to solve the integral equations which are used in determining the admittance is explained. A negative conductance is obtained when drifting carrier velocity is slightly exceed the fundamental wave velocity indicates the significant condition of the interaction. A brief analysis and discussion on the Dyakonov-Shur THz surface wave in 2DEG is also presented.