Resonant circular patch microstrip antenna with air gap
The resonant frequency and bandwidth characteristics of superstrate loaded air gap tuned circular patch microstrip antenna are investigated for different structural parameters. The problem is formulated in spectral domain and Galerkin's method is used for the solution. It is shown that adjustable air gap between the ground plane and substrate compensates superstrate loading effect on the resonant frequency, increases bandwidth and provides tunable operational characteristics.
Hankel transform domain analysis of dual-frequency stacked circular-disk and annular-ring microstrip antennas
A theoretical and numerical analysis of the dual-frequency stacked circular-disk and annular-ring microstrip antennas is discussed. The problem is formulated in the Hankel transform domain. First, the Green's function is derived, relating the transformed electric surface currents on the patches and the transformed tangential electric field components on the substrates. Galerkin's method is used with Parseval's relation for Hankel transformation to solve for the resonant frequencies and the unknown currents. The far-zone radiation patterns are expressed in terms of the transforms of the currents. Numerical results obtained for the resonant frequencies and radiation patterns are found to be in excellent agreement with the experimental data available in the literature. >
Effect of stress conditions on collapse deformation behavior of a rockfill material
A set of saturated and dry-saturated large-scale triaxial tests were conducted in order to explore the effects of stress conditions on the saturation-induced collapse deformation behavior of a rockfill material. Specimens were tested in different confining pressures and for dry-saturated tests the specimens were submerged in various shear stress levels. The results indicate that in all of the dry-saturated tests a sudden reduction in the volume of the specimens was observed during the submerging process. The ratio of the minimum axial strength of a submerged specimen (at the end of the saturation process) to the shear strength of the specimen before saturation is defined as the coefficient of stress recovery, Csr. Results of the dry-saturated tests showed that this ratio increases as the confining pressure increases and decreases by increasing the shear stress level. According to the results of dry-saturated tests the values of internal friction angle reduction caused by saturation (Δϕc), the ratio of the elasticity modulus of the material after saturation to its elasticity modulus in dry condition, i.e., Ewet/Edry, and also the saturation induced sudden volumetric strain (εvc) decrease as the confining pressure increases. However the shear stress level does not have any meaningful effect on the variation of Dfc, Ewet/Edry and (εvc).