Dual Mode Helix Antenna for wideband terrestrial and GPS L2 communications

In this paper a Dual Mode Helix Antenna (DMHA) for wideband terrestrial and GPS L2 communication is presented with a Side Fed Bifilar Helix Antenna (SFBHA) enclosed in a top fed Quadrifilar Helix Antenna (QHA). When the SFBHA is excited and the QHA is kept passive, the DMHA operates in linearly polarized terrestrial mode. For the satellite communication the QHA is top fed with two 90° out of phase feeds to provide circular polarization and SFBHA is kept passive. The QHA is made to resonate for GPS L2 (1227.75 ± 10 MHz) communication in satellite mode. Simulation results have shown that the bandwidth of the antenna is 850 MHz (1230 MHz - 2080 MHz) in terrestrial mode with nearly omni-directional radiation pattern and 40 MHz (1208 MHz - 1247 MHz) with nearly hemispherical radiation pattern in satellite mode. Measured results show that the bandwidth of the antenna is greater than 2GHz in terrestrial mode with nearly omni-directional radiation pattern and greater than 70 MHz in satellite mode (for VSWR ≤ 2) with nearly hemispherical radiation pattern.