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/.
Theoretical study of hemispherical helical antenna loaded with dielectric resonator
The characteristics of the hemispherical helical antenna loaded with dielectric resonator are investigated using surface integral equations based on the EFIE and PMCHW formulations (E-PMCHW), which are solved by the method of moments (MoM). Numerical results for the input impedances and axial ratio on the dielectric constant are presented for demonstrating that the hemispherical helical antenna with dielectric resonator can still produce circular polarization waves over a wide angular coverage. This makes it possible to reduce the size of the helical antenna so that it can meet the needs of practical applications.
Broadband quasi-taper helical antennas
A unique approach is described for widening the bandwidth of a helical antenna with improved gain, pattern, and axial ratio characteristics. The antenna may be described as a nonuniform or quasi-taper helix, which consists of a combination of uniform and tapered helix sections. Measured patterns, gain, axial ratio, and VSWR for various helical antenna configurations are presented and compared. It is shown that a nonuniform quasi-taper helix can provide an operating bandwidth twice that of a conventional uniform-diameter helix.