Mohsen Yazdani

Electromagnetic plane wave scattering by a radially uniaxial dielectric sphere: Debye series solution

In this paper, we examine the electromagnetic plane wave scattering by a uniaxial dielectric sphere using the generalized Debye series theory. With the aim of Debye series formulation, the generalized Mie series coefficients are replaced by infinite series of partial wave contributions that are diffracted, reflected and refracted following by p-1 internal reflections in the sphere. In addition to exploring the bistatic Radar Cross Section (RCS) of the positive/negative uniaxial dielectric spheres using Lorenz-Mie theory, the first three terms of generalized Debye series are investigated and the results are applied to improve our understanding of scattering mechanism from a uniaxial dielectric sphere.

Scattering from a large uniaxial dielectric sphere

The high frequency backscattering by a large uniaxial dielectric sphere is presented in this paper. Using the modified Watson method we transform the slowly convergent Mie series of the uniaxial dielectric sphere into a rapidly converging contour integral. The Mie series coefficients are then replaced by the geometric optics portion of the generalized Debye series for uniaxial dielectric sphere. With the aid of Debyes asymptotic formula, the contour integral is simplified and then computed using the saddle point method. A High frequency backscattering formula is proposed and the monostatic radar cross section (RCS) of a large uniaxial dielectric sphere is calculated. The results are compared with those computed using Lorentz-Mie theory.

Ultra-wide stopband in a compact low pass filter using stepped impedance resonators and novel techniques

The design procedure of a compact ultra-wideband (UWB) stepped impedance resonator (SIR) low pass filter, is presented in this paper. A SIR LPF with 7 GHz cutoff frequency miniaturized by meander line technique is designed and it is shown that offsetting the stepped impedance resonators, as well as indenting the tap location greatly improve rejection bandwidth. Offsetting input lines further maximizes rejection bandwidth. The proposed filter is simulated in Sonnet EM software, fabricated, and tested on a high dielectric ceramic. The results show an improved stopband performance compared with similar topologies with a drastic size reduction in the filter.

High-Frequency Scattering From Radially Uniaxial Dielectric Sphere

High-frequency backscattering caused by a large uniaxial dielectric sphere is presented in this letter. The term high frequency implies Ka ≫ 1 where K and a are the propagation constant and radius of the sphere, respectively. Using a modified Watson transformation, the slowly convergent generalized Mie series summation for a uniaxial dielectric sphere is transformed into a rapidly convergent contour integral. The generalized Debye series of the uniaxial dielectric spheres is introduced, and the Mie series coefficients are replaced by their equivalent Debye series formulations. An expression for the high-frequency backscattered field is proposed, and the monostatic radar cross section (RCS) of a large uniaxial dielectric sphere is calculated.

A UWB 1 to 4 wilkinson power divider with triple high-Q band-notched characteristic using U-shaped DGS

Reducing the interference between ultra wideband (UWB) and existing wireless communication systems has become of importance recently. In this study, we propose an equal 1 to 4 power divider (PD) which enables the suppression of three different frequencies, 3.95, 5.2 and 5.8 GHz, in the UWB frequency band by means of U-shaped defected ground structure (DGS). In this respect, it is essential to provide steep band-rejection with high Q-factor. The authors have used a novel method to attain this goal using U-shaped DGS. Studies show that there is a relation between the line width and Q-factor of a given band-notched structure. Therefore, instead of using a 50-50-50 ohm configuration, a 50-100-50 ohm transformation is used which has a narrower line width in the middle of the PD providing a steeper suppression with a high Q-factor. The measured Q-factor compared to similar structures is higher having a value of 27.5 with more than 30 dB suppression.

Transient Electromagnetic Scattering by a Radially Uniaxial Dielectric Sphere: The Generalized Debye and Mie Series Solutions

In this paper, a theoretical study is carried out to determine the scattering of a transient electromagnetics wave by a radially uniaxial dielectric sphere. This is achieved by inverse Laplace transformation of the frequency-domain scattering solution. To improve understanding of the scattering mechanism from a uniaxial dielectric sphere, two different frequency-domain solutions are employed. In the first approach, the impulse and step responses of a uniaxial dielectric sphere are evaluated by the Mie series solution. Following the high-frequency (HF) scattering solution of a large uniaxial sphere, the Mie series summation is split into high-frequency (HF) and low-frequency terms where the HF term is replaced by its asymptotic expression allowing a significant reduction in computation time of the numerical Bromwich integral. In the second approach, the generalized Debye series solution is introduced, and the generalized Mie series coefficients are replaced by their equivalent Debye series formulations. The results are then applied to evaluate the transient response of each individual Debye term allowing the identification of impulse returns in the transient response of a uniaxial sphere. The effect of variation in permittivity on the arrival time as well as amplitudes of each impulse return is studied, and the results are compared with those computed using the Mie series solution. The numerical results obtained from both methods are in complete agreement.

Ray Tracing Theory in a Radially Uniaxial Sphere

Ray tracing theory for a radially uniaxial dielectric sphere is presented in this communication. Reflection and transmission of the plane waves obliquely incident on the spherical interface between air and uniaxial are briefly examined and the general formulations for phase velocities as well as the refractive indices of the ordinary and extraordinary waves propagating in a radially uniaxial medium are investigated. The ray tracing method is implemented for both ordinary and extraordinary rays and the results are applied to evaluate the propagation paths and arrival times of the shortcut wave returns appearing in the transient backscattering response of a uniaxial dielectric sphere. The effect of the variation in relative permittivity on the arrival times of shortcut waves is studied. The results of the ray tracing method are compared with those computed using the Mie and Debye series solutions with good agreement.

Shortcut waves in a radially uniaxial sphere

Ray tracing theory for a uniaxial dielectric sphere is presented in this paper. The ordinary and extraordinary rays and waves in a uniaxial medium are studied. The reflection and transmission of the wave at the air-uniaxial boundary surface are investigated. The propagation path and the arrival time of the shortcut wave return in a uniaxial dielectric sphere are computed. The results are in good agreement with those provided by the Mie and Debye series solutions.