[pt] Neste estudo faz-se uma análise do desempenho de antenas
cônicas compactas para operar em largas bandas de
freqüência. Esta análise será feita observando o
comportamento da impedância da antena. Serão,
primeiramente, consideradas as estruturas convencionais
formadas por cones e cones sobrepostos próximos a um plano
condutor. Posteriormente, será considerada uma estrutura
cônica onde o arredondamento das bordas resulta em um
comportamento mais uniforme para a impedância de entrada
com variações da freqüência, conferindo um aumento na
banda para esta configuração. / [en] The discone antenna is well known as an easy to build
multioctave broadband antenna with a omnidirectional
radiation pattern in the H-plane, It comprises a plane
conductive disc element spaced close to and axially
aligned with a conductive cone element. For applications
in the UHF and microwave ranges, high performance antennas
have been designed to operate from 0.5 to 5 GHz with a
VSWR of about 3.5:1 or less. If the length is finite, the
impedance still strongly dependent on apex angle as long
as the cone is longer than about quarter of wavelength and
the apex angle is relatively larger. A problem that is
experienced with these antenna designs is the relatively
large size required to operate at the low frequencies. In
applications where utilization of this antenna. In this
work, the analysis and design of these antenna is obtained
by employing a rigorous formulation of the electromagnetic
scattering problem. As a design tool, we employ Method of
Moments for the analysis of rotationally symmetric
structures excited by TEM mode. To properly account the
variations in driven-point impedance with frequency, the
coaxial waveguide used to feed the antenna is also
included in the analysis. The excitation is simulated by a
distribution of equivalent electric and magnetic currents
placed inside the coaxial cable, over a cross-section
plane. These currents are defined such that only excite
the mode TEM towards the cable-antenna junction. These
numerical tool is employed in the shaping the metallic
surfaces involved in the discone-type antennas in order to
obtain more compact structures. Simple solutions can be
easily obtained making the center fed cone and the disc
element with radially outer edge portions rolled
backwardly and away from each other to form donut-shaped
configurations. The ruled edges not only reduce the
diameter of the antenna but also permit the current to
flow around them smoothly and without reflections that
degrade the VSWR at low end of the frequency band.
| Identifer | oai:union.ndltd.org:puc-rio.br/oai:MAXWELL.puc-rio.br:7300 |
| Date | 19 October 2005 |
| Creators | DENISE FREITAS SILVA |
| Contributors | JOSE RICARDO BERGMANN |
| Publisher | MAXWELL |
| Source Sets | PUC Rio |
| Language | Portuguese |
| Detected Language | English |
| Type | TEXTO |
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