S.K. Khamas

A Singly Fed Rectangular Dielectric Resonator Antenna With a Wideband Circular Polarization

A rectangular dielectric resonator antenna (DRA) that is excited using an outer-fed square spiral strip has been studied theoretically and experimentally. Utilizing such excitation has provided a circular polarization over a broad bandwidth of ~14% in conjunction with an impedance-matching bandwidth of ~11%. The structure has been rigorously modeled using a method of moments (MoM) model. A good agreement has been attained between computed and measured results.

A Singly Fed Wideband Circularly Polarized Dielectric Resonator Antenna Using Concentric Open Half-Loops

A rectangular dielectric resonator antenna (DRA) with a broadband circular polarization (CP) radiation is presented using a single feed excitation. A simple feed method is proposed using an open half-loop antenna that consists of three metallic strips. Utilizing such an excitation has provided a circular polarization over a bandwidth of 7% that has been increased further to 13% by adding a concentric parasitic open half-loop in the structure. This has been achieved in conjunction with a 20% impedance matching bandwidth over the same frequency range. The configuration has been rigorously modeled using a method of moments (MoM) model. The computed and measured results are in good agreement.

Moment-method analysis of printed wire spirals using curved piecewise sinusoidal subdomain basis and testing functions

Archimedian and logarithmic printed wire spirals are analyzed using a moment-method incorporating curved piecewise sinusoidal subdomain basis and testing functions. Results for spiral parameters including input impedance and current distribution are presented and are shown to have good agreement with published results for the same antennas obtained using linear segmentation. Since the curved basis functions exactly follow the spiral contour, significantly fewer curved segments are, therefore, required for accurate analysis compared with linear segmentation.

An Efficient Asymptotic Extraction Approach for the Green's Functions of Conformal Antennas in Multilayered Cylindrical Media

Asymptotic expressions are derived for the dyadic Greens functions of antennas radiating in the presence of a multilayered cylinder, where analytic representation of the asymptotic expansion coefficients eliminates the computational cost of numerical evaluation. As a result, the asymptotic extraction technique has been applied only once for a large summation order. In addition, the Hankel function singularity encountered for source and evaluation points at the same radius has been eliminated using analytical integration.

Electromagnetic Radiation by Antennas of Arbitrary Shape in a Layered Spherical Media

A unified method of moments model is developed for the analysis of arbitrarily shaped antennas that are radiating next to a multilayered dielectric sphere. The curvilinear Rao-Wilton-Glisson triangular basis functions and dyadic Greens functions have been used in the model. Antennas of various geometries including spherical, circular and rectangular microstrip antennas as well as hemispherical dielectric resonators have been modeled. Input impedance and radiation pattern results are presented and shown to be in good agreement with published data.

Moment Method Analysis of an Archimedean Spiral Printed on a Layered Dielectric Sphere

A method of moments model is presented to analyze Archimedean spirals that are printed on a layered dielectric sphere. The model is derived assuming an arbitrary location of the spiral. Input impedance, current distribution and far-field results are presented and are shown to be in good agreements with other methods.

Epitaxially Regrown GaAs-Based Photonic Crystal Surface-Emitting Laser

A GaAs-based epitaxially regrown photonic crystal surface-emitting laser is proposed and demonstrated at room temperature. The photonic crystal band-structure is mapped through the angular dependence of subthreshold electroluminescence, allowing the photonic crystal coupling coefficients to be determined.

Asymptotic Extraction Approach for Antennas in a Multilayered Spherical Media

An efficient algorithm is introduced to enhance the convergence of dyadic Greens functions (DGF) in a layered spherical media where asymptotic expressions have been developed. The formulated expressions involve an infinite series of spherical eigenmodes that can be reduced to the simple homogenous media Greens function using the addition theorem of spherical Hankel functions. Substantial improvements in the convergence speed have been attained by subtracting the asymptotic series representation from the original DGF. The subtracted components are then added to the solution using the homogenous media Greens function format.

Circularly Polarized Dielectric Resonator Antenna Excited by a Conformal Wire

A conformal spiral wire has been used to feed a dielectric resonator antenna to obtain a circular polarization. The parameters of the spiral have been optimized numerically so that minimum axial ratio (AR) and return losses are achieved. The method of moments (MoM) has been used in the analysis and the results have been validated against those from a commercial software package with a good agreement.

Optimisation of Coupling between Photonic Crystal and Active Elements in an Epitaxially Regrown GaAs Based Photonic Crystal Surface Emitting Laser

The waveguide design of a GaAs based, epitaxially regrown photonic crystal surface emitting laser is discussed so as to optimise the coupling of the photonic crystal and the mode overlap with the quantum wells. Design criteria include the positioning of the quantum well and the photonic crystal layers, and the effect of varying aluminium composition in the lower cladding layer. Room-temperature, pulsed laser oscillation is demonstrated.