Central-fed hemispherical helical antenna
The characteristics of a hemispherical helical antenna with central-fed are investigated by experiment. Results for a 3-turn hemispherical helix indicate that circular polarization can be obtained over a wide angular range with relatively high gain of about 8 dB. The frequency bandwidth for a 3-dB axial ratio criterion is /spl sim/11%, with a nearly resistive input impedance of 163 /spl Omega/.
Radiation characteristics of a spherical helical antenna
A helical antenna, consisting of a winding over a spherical surface, is proposed and investigated, both theoretically and experimentally. The winding is such that a constant spacing between turns is maintained. It is fed coaxially, with the inner conductor forming the helical winding and the outer conductor becoming the ground plane. Radiation characteristics of the proposed spherical helix are calculated, using the method of moments, and compared with the measured results. The results of this investigation indicate that radiation properties of the spherical helix are markedly different from those of the conventional cylindrical helix. Of particular interest is that, over a certain bandwidth, the proposed helix is capable of providing circular polarisation over a broad beamwidth. This property and its compact size make the spherical helix attractive to mobile radio communication systems with low channel capacity.
A spherical helical antenna
A spherical helical antenna is proposed, and its radiation characteristics are analyzed using numerical methods and experimental measurements. The analysis has shown that the spherical helix is, in general, a broad-beam radiator and operates over a relatively wide bandwidth. Results are highlighted for a ten-turn helix which, under certain conditions, can provide circular polarization over a wide beamwidth. The broad-beam circularly polarized antenna has potential applications in communications systems with low channel capacity.<<ETX>>