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/.
Coaxial-feed axial mode hemispherical helical antenna
A coaxial-feed axial mode hemispherical helical antenna is studied experimentally and theoretically. Results for a 3-turn hemispherical helix indicate that circular polarisation can be obtained over a broad beamwidth. The gain bandwidth is ~33% and the peak gain is 7.6 dB. The input impedance shows that it is a standing wave antenna
Main-beam polarization properties of modified helical antennas
The polarization properties of modified helical antennas are investigated for a wide range of directions using a two-dimensional polarization diagram. The current distribution on the antenna and the radiated field are calculated for several variations of the antenna shape to show the influences of the helix design on the main-beam polarization characteristics. This extended knowledge about typical polarization diagrams yields conditions for the antenna design. Special emphasis is placed on the choice of the geometrical parameters for the open end and the feed region of the antenna to meet different system requirements. The calculated results are confirmed with measured polarization characteristics and radiation patterns for experimental helices. >