GPS IIR/IIR-M satellite antenna patterns released for worldwide use

Partnering with the U.S. Coast Guard Navigation Center (NAVCEN), U.S. Space Force and Lockheed Martin Space have released the GPS IIR/IIR-M satellite antenna patterns for worldwide public use.

Additionally, the Institute of Navigation has offered a related ION journal article free to the public to accompany the antenna patterns.

The files now available from NAVCEN include:

• The GPS Block IIR and IIR-M Broadcast L-Band Antenna Panel: Its Pattern and Performance (paper from Navigation: Journal of the Institute of Navigation, Winter 2015)
• GPS-Block-IIR-and-IIR-M-Antenna-Panel-Pattern (Presentation)
  • Appendix A — IIR and IIR-M SV-Specific Antenna Panel Patterns – Plots
  • Appendix B — IIR and IIR-M SV-Specific Antenna Panel Patterns – Data (Powerpoint download)
  • Appendix C — IIR and IIR-M SV-Specific Antenna Panel Patterns – Phase Data (Powerpoint download)

The GPS Block II Replenishment (IIR) space vehicle (SV) began improving upon its baseline design in 2003 with the launch of the first Block IIR SV retrofitted with a redesigned  antenna panel. This is the Earth-facing panel providing the GPS L-band broadcast signal. The improved antenna panel includes redesigned L-band elements mounted on the SV Earth-facing structure in the same manner as the original antenna panel.

The Earth Terrestrial Service Volume is the near-Earth region up to 3,000 km altitude. (Diagram: NAVCEN/Lockheed Martin)

Spacecraft Navigation

The use of GPS signals for spacecraft navigation has increased in general over the last few decades. Navigation employing GPS observations for spacecraft in low-Earth orbit is now considered routine.

However, the situation is quite different for spacecraft that fly in the Space Service Volume above the GPS constellation, including medium-Earth orbit (MEO), geostationary orbit (GEO) and high-Earth orbit (HEO) satellites, as well as missions to the Moon and beyond.

For these spacecraft, reception of GPS transmit antenna side lobe signals is essential to improve availability and performance of on-board navigation and timing. In this context, the knowledge of the full antenna pattern (main lobe and side lobes) from the transmitting antennas of each of the GPS satellites is essential.

These published antenna patterns and associated ION citation describe both IIR and IIR-M antenna panel versions, their broadcast signal patterns, the performance observed in factory testing, and their on-orbit performance.

Chart: NAVCEN/Lockheed Martin

Chart: NAVCEN/Lockheed Martin

Chart: NAVCEN/Lockheed Martin

These patterns represent the current capability of the GPS IIR/IIR-M Space Vehicles. Receiver designers should consult the IS-GPS-200 specifications for use in receiver design and not base design on current signal performance.

GPS technical documents are also available at the NAVCEN website and linked from the GPS.gov website.

Legacy antenna panel on the GPS IIR satellite. (Photo: NAVCEN/Lockheed Martin)