Enhanced Low-Angle GPS Coverage Using Solid and Annular Microstrip Antennas on Folded and Drooped Ground Planes

Folded and drooped microstrip antennas are investigated in this communication for their potential applications in GPS marine navigation. Numerical and experimental results are reported to identify the effects of the percentage of the patch extending around to the folded side, position, and angle of the bend on the performance of the proposed antennas in comparison to the conventional flat counterparts. The folded antennas provide marginally improved 3-dB beam width and excellent phase center stability without degrading the bore-sight gain. A novel drooped square annular element operating in the TM ₃₀ mode is proposed and validated both numerically and experimentally. The drooped annular antenna is shown to have substantially improved above-horizon coverage to suit applications requiring acquisition of satellites from horizon to horizon with a pattern ripple less than 2 dB over the upper hemisphere and with an impedance bandwidth of 2%. The polarization rejection is marginally degraded at bore-sight. At the horizon, the cross component becomes dominant by 1.5 dB.