ANTEX 2.0 Format Examples and Test Data
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The present test data comprise a basic set of ANTEX 2.0 files for 
familiarization  with the proposed format and for final consolidation of 
the new ANTEX standard. All files use the provisional extension ".atx2" to 
ease distinction of old (ANTEX 1.4) and new (ANTEX 2.0) versions. 

  example.atx2            A set of sample antenna data illustrating the 
                          encoding of phase variations, group delay variations,
                          and gain patterns of GNSS satellite and receiver 
                          antennas in ANTEX 2.0. The data are mainly intended 
                          for illustration of the format and do not constitute
                          final antenna models for operational use.
                  
  igs20_2317_rcv.atx2     An ANTEX 2.0 version of the receiver antenna models 
                          in the latest IGS antenna model igs20_2317.atx.  
                          Common patterns for different bands have been 
                          aggregated, and the lists of equivalent frequency 
                          bands for L1, L2, L5, E5b,and E5ab have been 
                          expanded to explicitly provide antenna patterns for 
                          other constellations using the same bands.
  
  igs20_2317_sat.atx2     An ANTEX 2.0 version of the satellite antenna models 
                          in the latest IGS antenna model igs20_2317.atx. 
                          Validity intervals have been aggregatd to cover the 
                          full  operational period from first transmission 
                          irrespective of any SVN/PRN switches. Typically, 
                          antenna parameters are constant over the operational
                          lifetime, so only a single validity interval per 
                          satellite is specified. As an exception, multiple 
                          intervals are provided for antennas of selected 
                          GLONASS satellites to cover apparent phase center
                          changes that are potentially related to failures 
                          in the antenna hardware.
                          
  igs20_2317_satnew.atx2  A modified version of igs20_2317_sat.atx2, in which 
                          the new satellites antenna names defined as part of 
                          the IGS satellite metadata SINEX file have been 
                          introduced. Among others, this allows proper
                          distinction of BeiDou-3 SECM-A and SECM-B antenna
                          patterns and prepares for the support of multiple
                          antennas on GLONASS-M+/K1/K2 and QZSS satellites.

The ANTEX 2.0 format is largely self-explanatory and follows the basic format 
and layout of ANTEX 1.4. Changes w.r.t. vrsion 1.4  relate to better 
harmonization of satellite and receiver antenna models and to accommodation
of new features.

 - Satellite antennas are no longer referenced via a PRN but by the 
   satellite/hardware-specific SVN to avoid undue redundancy. The time 
   varying PRN/SVN associations required for finding the applicable antenna 
   pattern in the processing of RINEX observation data are provided in
   the IGS satellite meta data file (https://igs.org/mgex/metadata/#metadata). 

 - For supporting three types of antenna patterns (phase group delay, gain)
   new key words are used in the respective sections of the antenna description
   (e.g. "START OF PHV", "START OF GDV", and "START OF GAIN" replacing the
   former "START OF FREQUENCY").

 - For an unambiguous distinction of satellite and receiver antennas, different 
   Antenna type keywords “TYPE / SVN / SAT ID” and “TYPE / SN” are used.

 - Phase center offsets of all (i.e., satellite and receiver) antennas are 
   consistently provided with respect to the axes of a right-handed XYZ 
   antenna coordinate system. The "NORTH / EAST / UP" keyword is phased out
   and replaced by the new "X / Y / Z" keyword. For GNSS satellite antennas, 
   the antenna coordinate system is assumed to be aligned with the IGS 
   spacecraft body system. For the receiver antennas, the y-axis is defined 
   by the North marker and assumed to be aligned with local North for 
   permanent reference stations. In all cases, azimuth is counted clock-wise 
   from the y-axis to the x-axis and the off-boresight angle is measured from
   the z-axis to the x/y-plane. For receiver antennas, please note the 
   different order of PCO components in the X/Y sequence of ANTEX 2.0 
   compared to the N/E order used in ANTEX 1.4.

-  ANTEX 2.0 allows provision of a list of frequency bands (e.g., 
   "G01 S01 E01 J01") in the "START OF PHV", "START OF GDV", and 
   "START OF GAIN" lines to aggregate identical pattern specifications for
   different constellation-specific frequency band identifiers. This
   helps to avoid redundancy and allows controlled substitution of antenna
   patterns in the case of missing calibrations for individual frequencies.
   
Along with these changes, the provision of file-specific metadata is suggested
for the ANTEX 2.0 format. More specifically, three header keywords 
  
 ANTENNA TYPES
 REFERENCE FRAME 
 RELEASE     

may be considered to indicate the types of antennas in a file (SATELLITES, 
RECEIVERS, or MIXED), the terrestrial reference frame (e.g. IGS20, to 
indicate the inherent scale of satellite PCOs calibrations; only for satellite 
antenna data)  and teh release data (GPS week; e.g., 2317) of an antenna 
model in analogy with  current IGS antenna model conventions. Use of these 
(and possibly other header keywords) should be discussed as part of the 
evaluation phase prior to establishing a formal ANTEX 2.0 format description.