A circularly polarized crossed drooping dipole antenna

The authors present engineering and flight model results for a crossed drooping dipole antenna that was designed to provide hemispherical coverage for the telecommunications system onboard the NASA/JPL Galileo spacecraft. A split-tube balun was used for impedance matching within the frequency band of 2115-2295 MHz. Antenna gain patterns are shown; peak gains of 5.3 dBi were achieved at both frequencies for the flight model. The measured results are compared with the requirements. Higher than expected gain results were achieved; however, this was partially offset by the higher-than-expected axial ratios measured at the top end of the band. An engineering model antenna was developed to investigate the effects of varying the lengths of the dipoles, the distance from the dipoles to the tip of the mast, and the height of the dipoles over the ground plane. By systematically varying these parameters, peak-on-axis, dip-on-axis (bi-lobed), or tri-lobed patterns could be achieved.<>