Showing papers by "Craig R. Birtcher published in 2013"

Reflection Phase Characterization of Curved High Impedance Surfaces

Abstract: Reflection phase characteristics of cylindrically curved high impedance surfaces (HISs) are examined. Due to the non-periodicity of the problem, full wave solutions can be time consuming. To overcome this problem, an approximate semi-analytical method, which assumes a homogenized model for the curved HIS, is developed. The model parameters can be extracted from the reflection properties of the flat HIS. For the cases where only Floquet currents are excited, the reflection phase diagram of a curved HIS is independent of the curvature. However, the surface waves generated on HISs, due to their periodic geometry, distorts their reflection phase characteristics within specific frequency intervals. In those intervals, the reflection phase changes as a function of radius of curvature and size of the HIS. These effects are not observed for the flat cases because of the lower radiation resistance of the surface waves. In this paper, the normal incidence case is considered for TEz and TMz polarizations.

Impact of Finite Ground Plane Edge Diffractions on Radiation Patterns of Aperture Antennas (Invited Paper)

Abstract: In this study, the impact of flnite ground plane edge difiractions on the amplitude patterns of aperture antennas is examined. The Uniform Theory of Difiraction (UTD) and the Geometrical Optics (GO) methods are utilized to calculate the amplitude patterns of a conical horn, and rectangular and circular waveguide apertures mounted on square and circular flnite ground planes. The electric fleld distribution over the antenna aperture is obtained by a modal method, and then it is employed to calculate the geometrical optics fleld using the aperture integration method. The UTD is then applied to evaluate the difiraction from the ground planes' edges. Far-zone amplitude patterns in the E and H planes are flnally obtained by the vectorial summation of the GO and UTD flelds. In this paper, to accurately predict the H-plane amplitude patterns of circular and rectangular apertures mounted on square ground planes, the E-plane edge difiractions need to be included because the E-plane edge difiractions are much more intense than those of the H-plane edge regular and slope difiractions. Validity of the analysis is established by satisfactory agreement between the predicted and measured data and those simulated by Ansoft's High Frequency Structure Simulator (HFSS). Good agreement is observed for all cases considered.

Gain and Bandwidth Enhancement of Ferrite-Loaded CBS Antenna Using Material Shaping and Positioning

Abstract: Loading a cavity-backed slot (CBS) antenna with ferrite material and applying a biasing static magnetic field can be used to control its resonant frequency. Such a mechanism results in a frequency-reconfigurable antenna. However, placing a lossy ferrite material inside the cavity reduces the gain and impacts the impedance bandwidth. This letter develops guidelines, based on a nonuniform applied magnetic field and nonuniform magnetic field internal to the ferrite specimen, for the design of ferrite-loaded CBS that enhance its gain and tunable bandwidth by shaping the ferrite specimen and judiciously locating it within the cavity. To validate the modeling, simulations were performed using ANSYS's Maxwell 3D and HFSS, and they were compared to measurements conducted in the Arizona State University (ASU) anechoic chamber.

Conical Horn: Gain and Amplitude Patterns

Abstract: The conical horn radiation characteristics (gain, aperture phase distributions, loss factors, and amplitude patterns) are revisited based on the spherical and quadratic aperture phase distributions. Calculations of the conical horn gain, using over the aperture either the dominant -mode of a circular waveguide or the modal variations of a conical waveguide, are calculated using the aperture phase distribution represented by spherical and quadratic wavefronts. The gains are compared with the classical data by Gray and Schelkunoff, in an attempt to confirm their validity and accuracy and to determine whether they were derived based on spherical or quadratic phase distribution. In addition, more accurate loss factors, to account for amplitude and phase tapering over the conical horn aperture, are derived which improve the conical horn gain. New formulas for the design of optimum gain conical horns, based on the more accurate spherical aperture phase distribution, are derived and reported, and guidelines are provided for their utility. This paper also introduces a method to calculate accurately the far-zone amplitude patterns in the E and H planes, including those in the far side and back lobe regions, of a conical horn by utilizing geometrical optics and diffraction theory.

Surface wave suppression properties of Perforated Artificial Impedance Surfaces

Abstract: Surface wave suppression properties of Perforated Artificial Impedance Surfaces (PAIS) are investigated. It is shown that, by a proper choice of perforation geometry, surface wave propagation can be suppressed without the need of vias. This significantly decreases fabrication costs. It is also possible to overlap the surface wave suppression and reflection phase bands of the PAIS. Due to the rotational asymmetry of the structure, surface wave suppression is achieved in only one direction.

The Impact of Non-Uniform Bias Field on the Radiation Patterns of Ferrite-Loaded CBS Antennas

Abstract: Modeling of ferrite-loaded CBS antennas often makes use of the simplifying assumptions which involve some kind of averaging of the magnetic bias field. Simulations and measurements presented here demonstrate that failure to account for the non-uniform magnitude, as well as direction, of the bias field leads to inaccurate predictions of not only the input impedance, but also of the amplitude radiation patterns.

Amplitude patterns of aperture antennas mounted on circular and square ground planes

Abstract: The analysis for the far-zone amplitude radiation patterns in E and H planes of a TE11-mode circular aperture antenna mounted on finite circular and square ground planes is presented. The pattern is constructed from the superposition of a wave radiated directly from the circular aperture (in the presence of an infinite ground plane) and a wave diffracted from the edge of the finite ground planes. These patterns are verified with experimental results and those simulated by Ansoft's High Frequency Structure Simulator (HFSS). Excellent agreement is observed for all cases considered.

Surface wave effects on the reflection phase of curved High Impedance Surfaces

Abstract: For most cases, the reflection phase diagram of a curved High Impedance Surface (HIS) is independent of the curvature. However, the surface waves generated on HISs, due to their periodic geometry, distorts their reflection characteristics within specific frequency intervals. In those intervals, the reflection phase changes as a function of radius of curvature and size of the HIS. These effects are not observed for the flat cases because of the lower radiation resistance of the surface waves.

Improved gain and loss factor formulas for a conical horn

Abstract: The gain and loss factor of the conical horn are revisited based on the spherical and quadratic aperture phase distributions. The gains are compared with the classical data by Gray and Schelkunoff which appeared in the paper by King, in an attempt to confirm their validity and accuracy and to determine whether they were derived based on spherical or quadratic phase distribution. In addition, more accurate loss factors, to account for amplitude and phase tapering over the conical horn aperture, are derived which improve the prediction of the conical horn gain. New formulas for the design of optimum gain conical horns, based on the more accurate spherical aperture phase distribution, are derived and reported, and guidelines are provided for their utility.