A Dual-Band Reduced-Surface-Wave GPS Microstrip Antenna with Low Susceptibility to Multipath

L.I. Basilio, R.L. Chen, J.T. Williams, D.R. Jackson

Abstract:	Recently, a new type of microstrip antenna called the "reduced-surface-wave" (RSW) microstrip antenna has been introduced [1], [2]. The antenna is a shorted-annual-ring (SAR) microstrip antenna element, consisting of a circular microstrip patch of radius b with a short-circuit boundary at radius a < b. The outer radius b is chosen to satisfy the "reduced-surface-wave design condition" to reduce the surface-wave excitation and lateral radiation. The radius of the inner short-circuit wall is chosen to make the antenna resonant at the design frequency. In practice, the short-circuit wall is realized by a circular ring of conducting vias that connect the patch to the ground plane at radius a. This type of antenna excites less surface-wave fields and lateral (horizontally-propagating) radiation than does a conventional microstrip antenna. This means that there is less radiation that propagates along the horizon away from the antenna, and hence less edge diffraction off the edges of the substrate and ground plane. The result is an antenna with less radiation in the back-side region (behind the ground plane), and more ideal (smoother) patterns in the forward region. Such an antenna is less susceptible to low-angle multipath signals such as those emanating from ground bounces or structural reflection. Another advantage of the RSW microstrip antenna is that is has E and H-plane patterns that are more nearly equal in beamwidth than for a conventional microstrip antenna. This implies that the RSW antenna will have better circular polarization (lower cross-polarization) when fed with orthogonal feeds that are 90 degrees apart in phase. The use of the RSW microstrip antenna to achieve right-handed circularly polarized (RHCP) patterns with low back-side radiation and cross-polarization for high-precision GPS was demonstrated recently for a single-frequency antenna operating at the L1 band [3]. In the present work, a dual-band RSW microstrip antenna is introduced and studied. The purpose of making a circularly-polarized RSW antenna dual band is to allow for signal reception at both the L1 and L2 GPS bands, which is often required for high-precision applications. The dual-band design is accomplished by first introducing a new type of RSW microstrip antenna called the "inverted-shorted-annual-ring" (ISAR) design that has the radiating edge on the inside of the short-circuit wall. This unique design allows for another antenna, and in particular, a SAR-RSW antenna, to be placed inside the ISAR-RSW antenna. The SAR and ISAR antennas are designed to be resonant at the L1 and L2 bands, respectively.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	1870 - 1882
Cite this article:	Basilio, L.I., Chen, R.L., Williams, J.T., Jackson, D.R., "A Dual-Band Reduced-Surface-Wave GPS Microstrip Antenna with Low Susceptibility to Multipath," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 1870-1882.
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