Array antennas for DGPS

Multipath interference limits the speed and accuracy of determining position by `differential´ GPS techniques. A geodetic surveyor, for example, requires multipath interference rejection of about 36+20 log₁₀ sin ε dB, where ε is the elevation angle of the satellite being observed. Signal processing in a GPS receiver cannot satisfy this requirement. A receiving antenna is required that can sufficiently reject signals arriving from below the horizon. Available antennas have inadequate rejection, and brute-force methods of improving them, e.g., by enlarging their ground-planes, are impractical. A compact, ground-plane-less, dual-band, GPS antenna with improved multipath rejection has been designed and field-tested. This antenna resembles a vertical post rather than a horizontal platter; within its 0.1-m diameter, 0.4-m tall radome is a vertical array of turnstile elements. In field tests, a three-element array antenna rejected multipath better than a 0.5-m diameter ground-plane antenna by an average of 5 dB. A five-element array antenna appears superior to a 0.9-m diameter ground-plane antenna