GNSS Gain Characterization Data

ODTK provides a gain geometry data file alongside the GNSS catalog files in C:\ProgramData\AGI\ODTK 7\Databases\GNSS. This data file, GNSSGainGeometry.txt, describes the extent of the lobes in the antenna gain patterns produced by different GNSS constellations and blocks.

The L1 GPS data within the file has been processed using the raw data supplied publicly by NASA under the name “GPS Antenna Characterization Experiment Data” at https://esc.gsfc.nasa.gov/projects/PNT?tab=publications. Experimental observations at GEO were conducted using the L1 signals of GPS satellites to construct antenna patterns for major GPS blocks. Though data is also available on a per-satellite basis, the gain geometry data file only accounts for the average antenna gain pattern for different GNSS blocks. This is because there is minimal variance between antenna patterns for satellites of the same block. For a greater insight into this data, please see the paper “Characterization of On-Orbit GPS Transmit Antenna Patterns for Space Users” by Jennifer E. Donaldson et. al.

ODTK uses this data file when the GainPatternConstraint is active for GNSS Constellations and Satellites during the generation of simulated measurements. If the data file does not contain data for a satellite’s constellation, block, and signal type, ODTK will issue a warning message indicating that it will use a default field of view instead. If the data file does contain an entry for the satellite, the field of view will be cone-like with a vertex at the satellite and an axis passing through the center of Earth. The antenna pattern data defines the extent of the cone-like FOV, extending up to the null of the lobe selected. For the main lobe of a typical GPS satellite, this will result in roughly a 20- to 40-degree half-angle FOV.