Multipath-Rejecting GPS Antennas
Charles C. Counselman III
Massachusetts Institute of Technology
Abstract
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
{30+20*log10[sin(e)]} dB, where e 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-planeless, 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 turn stile 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.
Author's address for correspondence:
Charles C. Counselman III
42 Crestview Road
Belmont, MA 02178-2108
Tel. 617-484-8172; fax 617-253-7939;
voice-mail 617-253-7902;
e-mail: ccc@space.mit.edu
and
Department of Earth, Atmospheric, and Planetary Sciences and
Center for Space Research
Massachusetts Institute of Technology
Cambridge, MA 02139