Monopole Structures Research Articles

Miniature Hook-Shaped Multiband Antenna for Mobile Applications

In this letter, a novel and compact printed monopole antenna is presented, which has a simple but effective radiating patch for multiband wireless communication systems and mobile devices. Operational bands covered simultaneously by the antenna include the following: UMTS (1920-2170 MHz), 2.4-GHz WLAN (2400-2484 MHz), mobile WiMAX (IEEE 802.16e 2500-2690 MHz), 5-GHz WLAN (5150-5350/5725-5825 MHz), and ITS (5795-6400 MHz). A parametric study is applied in the antenna design process to achieve the required operational frequency bands. Desired resonances can be tuned by adjusting the gaps between the radiating semicircular arms and central feed-line, as well as embedding a dielectric slot in the ground surface. The antenna has dimensions ~ 20×20×1 mm3, which is smaller than previously proposed monopole structures. The design concept was validated by fabricating the antenna prototype and measuring its characteristics. The measured results show the antenna exhibits omnidirectional radiation and appropriate gain.

Inner‐core vacillation cycles during the intensification of Hurricane Katrina

AbstractA simulation of Hurricane Katrina (2005) using the Australian Bureau of Meteorology's operational model for tropical‐cyclone prediction (TCLAPS) shows that the simulated vortex vacillates between almost symmetric and highly asymmetric phases. During the symmetric phase, the eyewall comprises elongated convective bands and both the low‐level potential vorticity (PV) and pseudo‐equivalent potential temperature θe fields exhibit a ring structure, with the maximum at some radius from the vortex centre. During this phase the mean flow intensifies comparatively rapidly, as the maximum acceleration of the mean tangential wind occurs near the radius of maximum mean tangential wind (RMW). In contrast, during the asymmetric phase the eyewall is more polygonal, with vortical hot towers (VHTs) located at the vertices. The low‐level PV and θe fields have monopole structures with the maximum at the centre. The intensification rate is lower than during the symmetric phase because the mean tangential wind accelerates most rapidly well within the RMW.The symmetric‐to‐asymmetric transition is accompanied by the development of VHTs within the eyewall. The VHTs are shown to be initiated by barotropic–convective instability associated with the ring‐like structure of PV in the eyewall where the convective instability is large. During the reverse asymmetric‐to‐symmetric transition, the VHTs weaken as the local vertical wind shear increases and the convective available potential energy is consumed by convection. The weakened VHTs move outwards, similar to vortex Rossby waves, and are stretched by the angular shear of the mean vortex. Simultaneously, the rapid filamentation zone outside the RMW weakens, becoming more favourable for the development of convection. The next symmetric phase emerges as the convection reorganizes into a more symmetric eyewall. It is proposed that vacillation cycles occur in young tropical cyclones and are distinct from the eyewall replacement cycles that tend to occur in strong and mature tropical cyclones. Copyright © 2011 Royal Meteorological Society

A Very Compact Ultrawideband Printed Omnidirectional Monopole Antenna

Abstract-A new form of the microstrip-fed monopole antenna with truncated ground plane is presented. In comparison to the previous monopole structures, the miniaturized antenna dimension is only about 11 (0.11λr) × 16 mm2 (0.17λr), where λr, is the wavelength of the lowest frequency of the band (i.e., 3.2 GHz). By only sequentially inserting the three notches with proper sizes and positions in two corners of the quasi-square radiating patch, very good radiation and impedance characteristics are obtained. The measured impedance bandwidth of the realized antenna with optimal parameters is from 3.9 to 21.4 GHz (5.5:1, 138%) for VSWR <;1.5. Moreover, unlike the conventional omnidirectional monopole antennas, the stability of the H-plane radiation patterns of the proposed antenna is maintained in omnidirectional form within the frequency bandwidth up to 16 GHz. The improvement process of the impedance and radiation properties is completely presented and discussed.

Multiband Ring Fractal Monopole Antenna for Mobile Devices

A new form of a hybrid design of a microstrip-fed parasitic coupled ring fractal monopole antenna with semiellipse ground plane is proposed for modern mobile devices having a wireless local area network (WLAN) module along with a Worldwide Interoperability for Microwave Access (WiMAX) function. In comparison to the previous monopole structures, the miniaturized antenna dimension is only about 25 × 25 × 1 mm3 , which is 15 times smaller than the previous proposed design. By only increasing the fractal iterations, very good impedance characteristics are obtained. Throughout this letter, the improvement process of the impedance and radiation properties is completely presented and discussed.

Dual-Band Planar Monopole Antenna for Multiband Mobile Systems

In this letter, a simple planar monopole antenna with two operating bands for multiband mobile systems application is proposed. The proposed antenna is composed of two inverted-L branches and an open stub for impedance tuning. Both branches are resonating as quarter-wavelength monopole structures. The antenna covers the 890970-MHz and 16702350-MHz bands. A modified design for 824895-MHz and 14402180-MHz bands can be easily achieved by narrowing the widths of the lower resonant branch and the open stub. Both simulation and experimental results for the antenna characteristics are presented and discussed.

On the Nature of Zonal Jet EOFs

Abstract Analytic results are obtained for the mean and covariance structure of an idealized zonal jet that fluctuates in strength, position, and width. Through a systematic perturbation analysis, the leading empirical orthogonal functions (EOFs) and principal component (PC) time series are obtained. These EOFs are built of linear combinations of basic patterns corresponding to monopole, dipole, and tripole structures. The analytic results demonstrate that in general the individual EOF modes cannot be interpreted in terms of individual physical processes. In particular, while the dipole EOF (similar to the leading EOF of the midlatitude zonal mean zonal wind) describes fluctuations in jet position to leading order, its time series also contains contributions from fluctuations in strength and width. No simple interpretations of the other EOFs in terms of strength, position, or width fluctuations are possible. Implications of these results for the use of EOF analysis to diagnose physical processes of variability are discussed.

Broadband liquid antenna

A new class of reconfigurable antenna based on monopole structures containing liquid dielectrics is presented. It was determined that the operating principle of this class of antenna is essentially that of a dielectric resonator, where salt (in solution) modifies the dielectric properties. The resonator column height determined the operating frequency, allowing match and frequency of operation to be fully tunable over 1–2.5 GHz while salinity mainly influences the bandwidth.

Gravitating global monopoles in extra dimensions and the braneworld concept

Multidimensional configurations with Minkowski external space-time and a spherical global monopole in extra dimensions are discussed in the context of the brane world concept. The monopole is formed with a hedgehog-like set of scalar fields \phi^i with a symmetry-breaking potential V depending on the magnitude \phi^2 = \phi^i \phi^i. All possible kinds of globally regular configurations are singled out without specifying the shape of V(\phi). These variants are governed by the maximum value \phi_m of the scalar field, characterizing the energy scale of symmetry breaking. If \phi_m < \phi_cr (where \phi_cr is a critical value of \phi related to the multidimensional Planck scale), the monopole reaches infinite radii while in the ``strong field regime'', when \phi_m\geq \phi_cr, the monopole may end with a cylinder of finite radius or possess two regular centers. The warp factors of monopoles with both infinite and finite radii may either exponentially grow or tend to finite constant values far from the center. All such configurations are shown to be able to trap test scalar matter, in striking contrast to RS2 type 5D models. The monopole structures obtained analytically are also found numerically for the Mexican hat potential with an additional parameter acting as a cosmological constant.

HOPF MAP AND QUANTIZATION ON SPHERE

Quantization of a system constrained to move on a sphere is considered by taking a square root of the "on sphere condition". We arrive at the fiber bundle structure of the Hopf map in S2 and S4. This leads to more geometrical understanding of monopole and instanton gauge structures that emerge in the course of quantization.

Experimental study of the dynamics of conditionally averaged structures in weakly developed electrostatic turbulence

An experimental study of coherent structures in the electrostatic turbulence observed in a steady-state operated, magnetized, cylindrical low-β argon plasma is presented. The conditional averaging technique is used to detect and to characterize large-scale conditional structures. The results of conditional averaging of a single drift wave mode are consistent with theoretical predictions and the data obtained by an azimuthal array of 64 Langmuir probes. In the turbulent regime, large monopole structures in the density fluctuations are identified, which develop by particle trapping due to associated potential structures. These structures lead to transport of particles across magnetic field lines, as evident from the trajectory of the structures. The comparison of the dynamics of conditional structures and unaveraged spatiotemporal structures suggests that they are of the same origin.

Monopole spectra in non-Abelian gauge theories

We study the continuum limit of the length spectrum of magnetic monopole structures found after various Abelian projections of pure gauge SU(2), including the maximally Abelian gauge. We comment on Gribov copies, and measurements of the string tension.

Rapid relaxation of an axisymmetric vortex

In this paper it is argued that a two-dimensional axisymmetric large Reynolds number (Re) monopole when perturbed will return to an axisymmetric state on a time scale (Re1/3) that is much faster than the viscous evolution time scale (Re). It is shown that an arbitrary perturbation can be broken into three pieces; first, an axisymmetric piece corresponding to a slight radial redistribution of vorticity; second, a translational piece which corresponds to a small displacement of the center of the original vortex; and finally, a nonaxisymmetric perturbation which decays on the Re1/3 time scale due to a shear/diffusion averaging mechanism studied by Rhines and Young [J. Fluid Mech. 133, 133 (1983)] for a passive scalar and Lundgren [Phys. Fluids 25, 2193 (1982)] for vorticity. This mechanism is verified numerically for the canonical example of a Lamb monopole. This result suggests a physical explanation for the persistence of monopole structures in large Reynolds flows, such as decaying turbulence.

New Giant Resonances in 172-MeVαScattering fromPb208

Spectra of 172-MeV ..cap alpha.. scattering from /sup 208/Pb indicate in addition to giant monopole and quadrupole excitation new giant resonance structures in hadron scattering at E/sub x/=17.5 +- 0.8 and 21.3 +- 0.8 MeV with corresponding widths of 4.8 +- 0.8 and 5.9 +- 0.8 MeV. The angular distributions indicate L=3 and 1 giving rise to an interpretation as isoscalar giant octupole resonance (17.5 MeVm 60% energy-weighted sum-rule strength), and isoscalar giant dipole resonance (21.3 MeV, 90% energy-weighted sum-rule strength).