Appendix 2.  Antenna Specifications

A.2.1  Introduction

Accurate and consistent modeling of the antenna phase centers continues to be one of the most vexing problems in GPS analysis.  For purposes of discussion it is useful to divide the problem into horizontal and vertical effects, and to consider for the latter the "absolute" and relative models.  

For most of the antennas there are horizontal offsets of a few millimeters of the L1 and/or L2 phase centers from the mechanical center of the antenna.  These are sometimes not repeatable among individual antennas of a particular type and can be over 5 mm for analyses using the ionospheric-free (LC) combination of L1 and L2 phase.  These offsts can be determined by measurements of the antenna phase pattern in an anechoic chamber [Schupler et al., 1991; Rocken et al., 1995] or by analysis of short baseline field measurements in which the antennas are rotated between sessions [Braun et al., 1996].

The vertical positions of the phase centers of all GPS antennas show significant elevation-dependent motions, which if not modeled make estimated station heights dependent on the elevation cutoff angle of the observations at each station.  The size of the effect can vary from a few millimeters for matched antennas in a regional network in which all stations have nearly the same horizon, to several centimeters for some combinations of mismatched antennas.  The vertical phase center, as a function of elevation angle, can be mapped for individual antennas using anechoic chamber measurements [Schupler et al., 1991] or differentially for pairs of antennas by estimating coefficients of a polynomial or spherical-harmonic model [Mader and McKay, 1996; Rothacher et al. 1995].  When the "absolute" models determined from anechoic chamber measurements are used in analyses of global tracking data, station heights differ 6-12 cm from values inferred from SLR and VLBI data, implying a GPS scale error of ~10–8 .  More likely, there is some aspect of the anechoic chamber measurements that is not yet understood.  The difference in elevation-dependent variations from anechoic chamber measurements of pairs of antennas, however, agree reasonably well (25%) with those inferred from estimated from field measurements over short baselines, allowing inference of the vertical phase center, independent of elevation-angle cutoff, at the level of about 5 mm for some antennas.  For others, the agreement is poorer, presumably indicating significant effects that depend on the electrical environment of the measurements.  For example, Elosequi et al. [1995] demonstrated centimeter-level effects from the pillar used to support the antenna.  

Although an effective "absolute" model for vertical offsets remains illusive, the IGS issued in June, 1996, a provisional differential model that represents usefully the mean vertical and horizontal offsets for many of the commonly used antennas [Rothacher and Mader, 1996].  This model, designated IGS_01, arbitrarily assumes no elevation-dependent terms for the Dorne-Margolin choke ring antennas used in the global network and applies elevation-dependent variations for other antennas    

GAMIT computes the instantaneous position of an antenna's phase center from the geodetic monument in three pieces.  File station.info records the vertical or slant distance from an accessible point on the antenna structure (specified in the entry) to the monument, and also any horizontal offsets of the center of antenna from the monument deriving from a setup error.  Subroutine lib/hisub.f converts these field measurement to an offset of the IGS-defined antenna reference point (ARP)—usually the bottom center of the pre-amp—from the monument using mechanical specifications hard-wired into the subroutine.  Finally, the instantaneous positions of the L1 and L2 phase centers with respect to the ARP are computed by subroutine model/phasecc.f using the constant or elevation and/or azimuth dependent model specified in table antmod.dat.   In deciding how to handle phase centers in your processing, you should recognize that millimeter-level accuracy in the vertical for mismatched antennas or long baselines is not yet possible, and therefore consistency may be more important than accuracy.  We currently recommend one of two options:  use of table antmod.dat.mit (in updates/tables), which has no elevation-dependent terms and constant offsets that are (mostly) consistent with prior GAMIT use and have been employed by SOPAC for the current (1995–97) processing and reprocessing; or table svnav.dat.igs, which has the June, 1996, IGS_01 model of constants and elevation-dependent terms.  For antennas not included in the current IGS model, you will have to insert offsets chosen arbitrarily or for consistency with previous processing.  Note two important features of phase center offsets:  1) elevation-dependent variations are highly correlated with the atmospheric zenith delay and are thus most important to model correctly when this parameter is being estimated; 2) elevation-dependent terms in the model are closely coupled with the constant offset and should be matched correctly in the table ( see, e.g., Rothacher et al., [1995]).  

The next seven sections describe the mechancal dimensions of antennas used with TI4100, Trimble, Rogue, Ashtech/Topcon, Macrometer, Sercel, and Leica receivers.  In Section A.2.9 we list the correspondences between the various antennas and the 6-character codes used to identify them in GAMIT code and tables.  We also reproduce and explain copies of the two distributed tables of offsets—antmod.dat.mit and antmod.dat.igs.  Section A.2.10 lists references for this appendix. 

A.2.2   TI 4100 Antennas

TI 4100 Conical Spiral

In field operations there are two conventional points on the antenna structure to which height measurements are referred:  the center and the outside edge of the base of the pre-amp.  Vertical measurements to the center of the base are designated DHPAB and are simply added to the table values to get the L1 and L2 phase centers.  Slant height measurements to the edge of the base are designated SLPAB and converted to vertical heights using the pythagorean rule and a base radius of 0.8415 m.

The values given in the antmod.dat.mit for the early series 100 and 2000 antennas, designated TI4100, are taken from Sims [1985].  For the newer and more common 4000 series antennas, designated TI4000, the values were determined by Schupler et al. [1992] and confirmed by our own analysis.   Use of the Schupler et al. variable phase-center model will increase the heights (relative to other antenna types) estimated from LC observations by about 15 mm.

TI 4100  FRPA-2 microstrip

These antennas have been used only at the CIGNET fiducial stations at Richmond (Florida), Mojave (California), and Kauai (Hawaii).   The offsets given in antmod.dat.mit are based on UNAVCO short baseline tests (personal communication, John Braun, 21 May 1994).  They are untested in MIT or SOPAC analyses. 

A.2.3   Trimble Antennas

Trimble 4000 SST

The 4000 SST antenna  ( TRMSST ) is a microstrip which has a round ground plane with horizonally scalloped and vertically beveled edges.  Below the ground plane is a small square box containing the pre-amp.  Field height measurements are commonly made to the outer edge of the ground plane—either the top, middle, or bottom of the beveled edge.   Subroutine hisub is coded to accept slant height measurements to the top (SLTGP, radius 0.2403 m), middle (SLMGP, radius 0.2413 m), or bottom (SLBGP, radius 0.2403 m) of the ground plane.  If the Trimble measuring rod is used, the height measurement is usually made to the inside of one or more of the notches (radius 0.2334), on either the top (SLTGN) or bottom (SLTBGN) of the ground plane.  The bottom of the ground plane is 0.060 m, the middle 0.0615 m, and the top 0.063 m above the ARP (base of pre-amp). 

With no elevation-dependent model, Trimble specifications and UNAVCO tests put the L1 phase center 6.2 mm above, and the L2 phase center 4.7 mm above the top of the ground plane.  Use of the variable phase-center model will increase heights estimated from LC observations by about 15 mm.  Rotation tests and anechoic chamber measurements suggest that there are differences of at least several millimeters, in both the vertical and horizontal directions (C. Rocken, personal communication, 1995; Rothacher and Mader, 1996).  The IGS_01 model reflects these differences. 

Trimble 4000 SSE

The antenna accompanying all but the first SSE receivers, and also SSi receivers, is different from the SST antenna in having separate microstrips for L1 and L2; it is usually designated "Geodetic L1/L2 and carries the GAMIT code TRMSSE. Subroutine hisub allows the same types of measurements but uses slightly different dimensions.  The bottom of the ground plane is 0.0556 m, the middle 0.0574 m, and the top 0.0591 above the ARP.  The radius to the edge of the ground plane (top, middle, or bottom) is 0.2415, and to the inside of the notches 0.2335 m.  

The no-model offsets given in antmod.dat.mit are currently set to be the same as for the SST antenna, as indicated by the manufacturer, but anechoic chamber and field measurements suggest that there are differences of at least several millimeters, in both the vertical and horizontal directions (C. Rocken, personal communication, 1995; Rothacher and Mader, 1996).

Trimble 4000 SLD

The 4000 SLD antenna is a microstrip which has a round ground plane with a smooth edge.  Below the ground plane is a square box containing the pre-amp.  Field measurements of the slant height are commonly made to the top (SLTGP) or bottom (SLBGP) edge of the ground plane or the bottom corner of the pre-amp base (SLPAC).   The bottom of the ground plane is 0.0529 m, and the top 0.0512 m above the pre-amp base, the ARP.   The ground plane has a radius of 0.2413 m, and the diagonal from the center to the corner of the pre-amp is 0.0991 m.  

According to the manufacturers specifications, the L1 phase center is 6.1 mm above the top of the ground plane or 0.0573 m above the ARP,  and the L2 phase center 4.5 mm above the top of the ground plane or 0.0557 m above the ARP, with no variable phase center model applied (UNAVCO communication from B. Perin, 6 Februeary, 1991).

Trimble 4000 SXD

The 4000 SXD antenna is a microstrip which has a square ground plane with rounded corners.  Below the ground plane is a square box containing the pre-amp.  Field measurements of slant height are commonly made to the bottom of the ground plane at one of the corners (SLCGP) or to the bottom corner of the pre-amp base (SLPAC).   The ground plane is 3.4 mm thick and the bottom is 0.048 m above the pre-amp base, the ARP.  The side of the ground plane is 0.3048 m and the diagonal (rounded) corner (the measurement point)  0.4153 m from the center.  The pre-amp has a half-width of 0.0984 m and a diagonal of 0.1391 m. 

According to the manufacturers specifications, the L1 phase center is 6.2 mm above the top of the ground plane or 0.0574 m above the ARP,  and the L2 phase center 4.6 mm above the top of the ground plane or 0.0558 m above the ARP, with no variable phase center model applied (UNAVCO communication from B. Perin, 6 February, 1991).

A.2.4   Rogue Antennas 

Dorne-Margolin with Choke Ring 

There are three antennas used with Rogue, MiniRogue, and TurboRogue receivers, all variations of a Dorne-Margolin element mounted with the circular ground plane and choke rings based on a JPL design.   The antennas used with the original Rogue SNR-8 were built at JPL and are designated model "R" (ROGSNR, DMRCHR, or ROGDMR); the early models built by Allen Osborne Associates (AOA) are designated model "B" (ROGAOA, DMBCHR, or ROGDMB); and the AOA models currently distributed with the TurboRogue are designated model "T" (TRBROG, DMTCHR, or ROGDMT,).  If the antenna is mounted on a tripod, height measurements are usually made to the bottom of the choke ring or an underlying baseplate.   If the antenna is spike-mounted on the ground, the measurement is made to the bottom of the baseplate.  In some permanent mounts surveyed by theodolite, the direct height may be specified to the the top of the choke rings (DHTCR).    

For the "R" model, the ARP is the bottom of a base plate, 0.381 mm in diameter and 6 mm thick.  The choke ring above is 64 mm high, so that the top of the choke ring is 70 mm above the ARP.   Measurements made to the bottom of the assembly are all to the ARP, whether designated "pre-amp base" (DHPAB) or  "bottom of choke ring"  (DHBCR or SLBCR).  

The "B" model replaced the thin baseplate with one 11 mm high and 351 mm in diameter, and increased the choke ring height to 70 mm.  For this model the ARP is the bottom of the choke rings, not the bottom of the baseplate, so that the top of the choke rings is still 70 mm above the ARP. 

The "T" model has a choke ring 67 mm high including the baseplate and a pre-amp 35 mm high.  The ARP is the bottom of the pre-amp, so that the top of the choke rings is 102 mm above the ARP.   The width of the choke rings is 381 mm.  

According to the manufacturers' nominal specifications, with no variable model, the L1 phase center is 8 mm, and the L2 phase center 26 mm above the top of the choke rings for all three models. 

A.2.5   Ashtech Antennas

There have been three models (with one additional variation) of the Ashtech dual-frequency micro-strip antennas.  The first two (both part #700228) both used a Ball Corporation microstrip patch and an external low-noise amplifier (LNA) but had different ground planes—one with closed holes for a measuring rod, the other with open holes.  The third model has a different microstrip patch and a larger ground plane.   The current high-precision antenna used with Z-12 receivers is a Dorne-Margolin, choke-ring design patterned after the TurboRogue (DM-T) antenna.  It can be used with or without a detachable radome.  

Ashtech L

The earlier model of the 700228 antenna was used mostly with the MD-XII (codeless) receiver and is designated the"Geodetic L1/L2" or "L" model (ASHL12).  It has a 28-cm ground plane with closed holes near the edge for measuring height.   Field measurements are commonly made by placing a measuring rod through holes 115 mm from the center near the outer edge of the ground plane (SLHGP or SLAGP).  The ground plane itself is rounded on the edge, with bottom outer edge 142.4 mm from the center.  The top of the ground plane, where the holes are located, is 64 mm above the base of the pre-amp (ARP). Subroutine hisub also supports slant height measurements to the outermost part of the bevel on the bottom of the ground plane (SLBGP).   There is a provision for adding extender sections to the ground plane, but this configuration has rarely been used and is not supported by hisub. 

Ashtech P/Topcon P

The later model of the 700228 was used chiefly with the Ashtech P12 and Topcon GP-RIDP receivers (but possibly also with the Ashtech Z-12 and Topcon GP-RIDY) and is designated the "Geodetic II L1/L2" or "P" (ASHP12/TOPP12).   It  also uses a 28-cm ground plane but with the holes open and at the edge, at a distance of 131.8 mm  from the center, and no ability to extend the ground plane.  The allowable measurement codes are the same as for the "L" model. 

Ashtech III/Topcon

The "Geodetic Antenna III" antenna  (ASHGD3/TOPGD3)  (part #700718) uses a different micro-strip patch and a larger (34-cm) ground plane (sometimes termed the "Whopper") with open holes.  It has been used with the Ashtech Z-12 and Topcon GP-RIDY receivers.  The antenna has an internal LNA in the center hub and a circular radome to improve azimuthal symmetry.   As for the L and P models, the top of the ground plane is 64 mm above the base of the pre-amp (ARP).  The radius of the ground plane is 173.7 mm, and the pre-amp 40.0 mm.  GAMIT supports measurement of the direct height to the top of the ground plane (DHTGP) and slant height to the outside of the holes (SLHGP or SLLGP).   

At the present time, the effective phase centers of the Ashtech microstrip  antennas is uncertain.  Short baseline GPS and anechoic chamber measurements give inconsistent results.  In table antmod.dat.mit we have maintained the offsets determined for Release 9.2, which place the L1 phase center ~33 mm, and the L2 phase center ~13 mm above the ground plane.  Previous GAMIT releases assumed that both L1 and L2 phase centers are in the ground plane.  The IGS_01 model in antmod.dat.igs gives elevation-dependent models for these antennas but they are based on limited, non-redundant tests and do not have the reliability of the models for the Trimble microstrip or the choke-ring antennas 

Ashtech Dorne-Margolin with Choke Ring 

The new Ashtech geodetic antenna is designed to be mechanically and electrically equivalent to the Turbo-Rogue ("T") antenna, which uses a Dorne-Margolin element with JPL choke rings.  The input options and offsets are currently the same as those applied for the DM-T, in both hisub and antmod.dat. The designation ASHDMG (or DMGASH) is intended to apply to use of the antenna without its radome, and ASHDMR (or DMRASH) to the antennas with the radome in place, but at present no distinction is made in either antmod.dat.mit or antmod.dat.igs.   Tests at UNAVCO [Rocken et al., 1995] and MIT [Niell et al., 1996] suggest that the phase center changes in vertical by 5–15 mm when the radome is used, but similar tests at AIUB (Bern) and NGS obtain differences less than 3 mm [Rothacher and Mader, 1996]. 

A.2.6  MACROMETER Antennas

Min-Mac 2816 AT 

The Macrometer antenna used with the Mini-Mac 2816 AT is a crossed dipole above a thick square ground plane ( MINXDP or MIN6AT ).  The ARP is the base of the ground plane structure, which contains the pre-amp.  GAMIT supports only direct height measurements to the ARP (DHPAB) or reference to the L1 phase center (L1PHC).  

According to the manufacturer's specifications, the L1 phase center is 107.1 mm, and the L2 phase center 91.7 mm above the ARP [J. Ladd, private communication, 1989].  Use of an elevation-dependent model corrects this by several centimeters.  

A.2.7  SERCEL Antennas

For the SERCEL TR5S and NR52 antennas, we have only scant information conveyed by K. Feigl from the log sheets for the Djibouti 1991 observations.  There are no mechanical dimensions coded in hisub, so that only measurements to the ARP (DHPAB) are allowed.  The difference between the L1 and L2 phase centers is unknown.   In antmod.dat, we currently give for the TR5S (SRTR5S) phase center offsets from the ARP of 264 mm for the TR5S (SRTR5S) and 210 mm for the NR52 (SRNR52). 

A.2.8  Leica Antennas

 For the Leica antennas we also have only limited information; no mechanical dimensions are coded in hisub.  By specifying an offset of the L1 and L2 phase centers in antmod.dat, however, you can use station.info entries to the ARP (DHPAB) or the L1 phase center (L1PHC) for the antenna mounted with the GRT 44 carrier (LEIGRT), the SR299/SR399 internal (SR299I), SR299/SR399 external with ground plane (SR299E), and SR299/SR399 external without groundplane (SR299G). 

A.2.9  Tables

The preferred designations of antennas are summarized in table rcvant.dat and reproduced below.  This table is used to get the full receiver and antenna names for the H-file (to be passed to a SINEX file) and by XTORX to write complete names into the RINEX header.  Acceptable aliases for some of the antennas are hardwired into subroutines hisub.f and ant_alias.f in gamit/lib and can be used for entries in antmod.dat and station.info.  They are given shown as comments in the table below.

 ANTENNAS
# Current aliases in gamit/lib/ant_alias.f :
#    ASHXII => ASHP12
#    DMGASH => ASHDMG
#    DMRASH => ASHDMR
#    DMRCHR => ROGSNR
#    DMBCHR => ROGAOA
#    DMTCHR => TRBROG  
#    DMGTRM => TRMDMG
#    MIN6AT => MINDXP
#    
#ANTCOD        ____FULL_NAME_______  |
#format(1x,a6,8x,a20)                |
 ASHL12        Ashtech Geodetic L    |  Dual freq. with LD-XII & MD-XII; 28-cm gp w/closed holes
 ASHLEX        Ashtech Geod L Ext    |  Geodetic L with extended sections added
 ASHP12        Ashtech Geodetic P    |  Dual freq. with P-12 and early Z-12; 28-cm gp w/ open holes
 ASHGD3        Ashtech Geodetic III  |  Dual freq. with Z-12; 34-cm gp w/ closed holes
 ASHDMR        Ashtech DM radome     |  Dorne Margolin with choke ring (with radome) 
 ASHDMG        Ashtech DM W/O radome |  Dorne Margolin with choke ring   
 FRPA-2        FRPA-2                |
 LEIGRT        Leica system 200      |
 MIN6AT        Macrometer X-Dipole   |  Crossed-dipole antenna with large ground plane
 MINXDP        Macrometer X-Dipole   |  Crossed-dipole antenna with large ground plane
 MINPCH        Minimac Patch         |
 SR299I        Leica SR299 Internal  |
 SR299E        Leica SR299E GP       |
 SR299W        Leica SR299E W/O GP   |
 ROGAOA        Dorne-Margolin B      |  Antenna with chokering for Rogues (AOA design) 
 ROGSNR        Dorne-Margolin R      |  Antenna with chokering for Rogues (JPL design)
 TRBROG        Dorne-Margolin T      |  Antenna with chokering for TurboRogues
 SRTR5S        Sercel TR5S           |
 SRNR52        Sercel NR52           |
 TI4100        TI 4100               |  Early 100 and 2000 series
 TI4000        TI 4000               |  Later 4000 series
 TRMSXD        4000SX Micro          |  (Square)
 TRMSLD        4000SLD L1/L2         |  Dual  freq. geodetic receiver (SLD series)  
 TRMSST        4000SST L1/L2 Geod    |  Dual freq. geodetic receiver (SST/SSE series)
 TRMSSE        TR Geod L1/L2 GP      |  Dual freq. geodetic receiver (SSE/SSI series)  
 TRMKIN        TR Geod L1/L2 W/O GP  | 
 TRMDMG        Trimble choke-ring    |  Dorne Margolin with choke ring
 WM-102        Wild WM-102           |
 END

Table antmod.dat.mit is shown below.  It reproduces reproduces phase-center-to-ARP values hard-wired into hisub.f values prior to GAMIT release 9.3 except for small corrections (2–4 mm) in the heights of the Trimble SXD and SLD, and the Ashtech P and L antennas.  

# ANTMOD.DAT table created from old HISUB.F routine 95/10/18; last mod rwk 97/01/17
# ANTYP freq   Up   North   East      Model        azinc elinc sign
 TI4100  L1  227.0    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0 
 TI4100  L2  202.0    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0 
 TI4000  L1  221.0    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0 
 TI4000  L2  198.0    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0 
 FRPA-2  L1  124.8    0.3    3.4  OLD_HISUB_VALUE    0     0    1.0 
 FRPA-2  L2   90.9   -0.9    2.2  OLD_HISUB_VALUE    0     0    1.0 
 TRMSLD  L1   57.3    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 TRMSLD  L2   55.7    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 TRMSXD  L1   57.4    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0 
 TRMSXD  L2   55.8    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 TRMSST  L1   69.2    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 TRMSST  L2   67.7    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 TRMSSE  L1   69.2    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 TRMSSE  L2   67.7    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 ASHL12  L1   97.0    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 ASHL12  L2   77.0    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0 
 ASHP12  L1   97.0    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 ASHP12  L2   77.0    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0 
 ASHGD3  L1   97.0    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 ASHGD3  L2   77.0    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0 
 ASHDMR  L1  109.5    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 ASHDMR  L2  128.0    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0   
 ASHDMG  L1  109.5    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0             
 ASHDMG  L2  128.0    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0   
 SRTR5S  L1  264.0    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 SRTR5S  L2  264.0    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 SRNR52  L1  210.0    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 SRNR52  L2  210.0    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 LEIGRT  L1   91.0    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 LEIGRT  L2   91.0    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0 
 WM-102  L1   66.0    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 WM-102  L2   66.0    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0    
 ROGSNR  L1   77.8    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 ROGSNR  L2   96.3    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 ROGAOA  L1   77.8    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 ROGAOA  L2   96.3    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 TRBROG  L1  109.5    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 TRBROG  L2  128.0    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0    
 MINXDP  L1  107.1    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0
 MINXDP  L2   91.7    0.0    0.0  OLD_HISUB_VALUE    0     0    1.0

A portion of table antmod.dat.igs is shown below.  

correct for the offsets you have to ADD the offset value to the antenna
#   height and the horizontal offsets. To apply the elevation-dependent 
#   calibration values you have to interpolate within the 5-degree elevation table 
#   to obtain the correction for the elevation angle of the satellite. 
#   The correction has to be ADDED to the computed distance between satellite
#   and receiver antenna or SUBTRACTED from the observations.
# ROWS ARE AZMITH, COLUMNS ARE ELEVATION ANGLE. (VERTIVAL PHASE CETRE CORRECTIONS ARE IN MILLIMETRES)
# ELV ANG 00    05    10    15    20    25    30    35    40    45    50    55    60    65    70    75    80    85    90
# ANTYP freq   Up   North   East      Model        azinc elinc sign
 TRBROG  L1  110.0    0.0    0.0  IGS_01           360    05    1.0  TURBOROGUE DORNE MARGOLIN T 
         0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0
         0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0
 TRBROG  L2  128.0    0.0    0.0  IGS_01           360    05    1.0  TURBOROGUE DORNE MARGOLIN T 
         0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0
         0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0
 ROGSNR  L1   78.0    0.0    0.0  IGS_01           360    05    1.0  ROGUE  DORNE MARGOLIN R
         0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0
         0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0
 ROGSNR  L2   96.0    0.0    0.0  IGS_01           360    05    1.0  ROGUE  DORNE MARGOLIN R
         0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0
         0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0
 ROGAOA  L1   78.0    0.0    0.0  IGS_01           360    05    1.0  ROGUE  DORNE MARGOLIN B
         0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0
         0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0
 ROGAOA  L2   96.0    0.0    0.0  IGS_01           360    05    1.0  ROGUE  DORNE MARGOLIN B
         0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0
         0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0
 TRMSST  L1   78.0    0.0   -3.0  IGS_01           360    05    1.0  TRIMBLE 4000ST L1/L2 GEOD     Mod. 14532
         0.0   0.0   7.0   7.3   8.5  10.2  11.4  13.0  14.6  15.8  16.3  16.4  15.7  13.7  10.2   6.3   3.1   1.1   0.0
         0.0   0.0   7.0   7.3   8.5  10.2  11.4  13.0  14.6  15.8  16.3  16.4  15.7  13.7  10.2   6.3   3.1   1.1   0.0
 TRMSST  L2   74.4   -3.1   -1.3  IGS_01           360    05    1.0  TRIMBLE 4000ST L1/L2 GEOD     Mod. 14532
         0.0   0.0   0.2   1.0   1.5   2.0   2.7   3.3   3.6   3.9   4.2   4.2   3.4   2.2   1.2   0.7   0.5   0.1   0.0
         0.0   0.0   0.2   1.0   1.5   2.0   2.7   3.3   3.6   3.9   4.2   4.2   3.4   2.2   1.2   0.7   0.5   0.1   0.0
 TRMSSE  L1   75.1    1.5   -1.2  IGS_01           360    05    1.0  TRIMBLE TR GEOD L1/L2 GP      Mod. 22020
         0.0   0.0   8.2   7.9   9.0  10.4  11.9  13.4  14.9  16.2  16.9  16.9  16.1  14.5  11.7   8.1   4.6   1.8   0.0
         0.0   0.0   8.2   7.9   9.0  10.4  11.9  13.4  14.9  16.2  16.9  16.9  16.1  14.5  11.7   8.1   4.6   1.8   0.0
 TRMSSE  L2   69.2   -1.1    1.7  IGS_01           360    05    1.0  TRIMBLE TR GEOD L1/L2 GP      Mod. 22020
         0.0   0.0   0.1   1.2   2.1   2.8   3.6   4.5   5.3   5.6   5.6   5.4   4.9   4.1   3.0   1.8   0.9   0.3   0.0
         0.0   0.0   0.1   1.2   2.1   2.8   3.6   4.5   5.3   5.6   5.6   5.4   4.9   4.1   3.0   1.8   0.9   0.3   0.0
 ASHL12  L1   79.9    0.3    0.5  IGS_01           360    05    1.0  ASHTECH 700228
         0.0   0.0   0.9   0.7   1.5   2.3   2.6   2.8   3.0   3.3   3.0   2.4   2.1   2.1   1.8   1.2   0.5   0.1   0.0
         0.0   0.0   0.9   0.7   1.5   2.3   2.6   2.8   3.0   3.3   3.0   2.4   2.1   2.1   1.8   1.2   0.5   0.1   0.0
 ASHL12  L2   79.2   -1.2    0.8  IGS_01           360    05    1.0  ASHTECH 700228
         0.0   0.0  -1.8   1.6   2.4   1.8   1.5   1.7   1.9   2.0   2.1   2.3   2.2   1.8   1.6   1.5   1.1   0.4   0.0
         0.0   0.0  -1.8   1.6   2.4   1.8   1.5   1.7   1.9   2.0   2.1   2.3   2.2   1.8   1.6   1.5   1.1   0.4   0.0
 ASHP12  L1   80.8   -0.2   -1.0  IGS_01           360    05    1.0  ASHTECH 700228 NOTCH
         0.0   0.0  -2.0  -0.3   1.0   1.8   2.4   2.8   3.0   3.1   3.0   2.9   2.6   2.4   2.1   1.7   1.3   0.7   0.0
         0.0   0.0  -2.0  -0.3   1.0   1.8   2.4   2.8   3.0   3.1   3.0   2.9   2.6   2.4   2.1   1.7   1.3   0.7   0.0
 ASHP12  L2   77.8   -1.9    3.8  IGS_01           360    05    1.0  ASHTECH 700228 NOTCH
         0.0   0.0  -2.3  -3.0  -3.1  -2.9  -2.5  -2.1  -1.8  -1.6  -1.5  -1.7  -2.0  -2.3  -2.6  -2.8  -2.5  -1.7   0.0
         0.0   0.0  -2.3  -3.0  -3.1  -2.9  -2.5  -2.1  -1.8  -1.6  -1.5  -1.7  -2.0  -2.3  -2.6  -2.8  -2.5  -1.7   0.0
 ASHGD3  L1   92.0  -0.7   0.4    IGS_01           360    05    1.0  ASHTECH 700829
         0.0   0.0  -1.5   0.5   2.6   4.8   6.8   8.6   9.9  10.7  11.0  10.8  10.0   8.7   7.1   5.3   3.3   1.5   0.0
         0.0   0.0  -1.5   0.5   2.6   4.8   6.8   8.6   9.9  10.7  11.0  10.8  10.0   8.7   7.1   5.3   3.3   1.5   0.0
 ASHGD3  L2   60.1  -0.1  -0.8    IGS_01           360    05    1.0  ASHTECH 700829
         0.0   0.0   0.3  -2.4  -4.2  -5.5  -6.3  -6.8  -7.0  -7.1  -7.1  -7.1  -6.9  -6.6  -6.1  -5.4  -4.2  -2.5   0.0
         0.0   0.0   0.3  -2.4  -4.2  -5.5  -6.3  -6.8  -7.0  -7.1  -7.1  -7.1  -6.9  -6.6  -6.1  -5.4  -4.2  -2.5   0.0
 ASHDMR  L1  110.0    0.0    0.0  IGS_01           360    05    1.0  ASHTECH 700936 DORNE MARGOLIN ASH With RADOME  
         0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0
         0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0
 ASHDMR  L2  128.0    0.0    0.0  IGS_01           360    05    1.0  ASHTECH 700936 RADOM MARGOLIN ASH With RADOME 
         0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0
         0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0
 ASHDMG  L1  110.0    0.0    0.0  IGS_01           360    05    1.0  ASHTECH DORNE MARGOLIN ASH    (no radom)
         0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0
         0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0
 ASHDMG  L2  128.0    0.0    0.0  IGS_01           360    05    1.0  ASHTECH DORNE MARGOLIN ASH    (no radom)
         0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0
         0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0   0.0
 SR299I  L1  113.1    3.1   -0.2  IGS_01           360    05    1.0  LEICA INTERNAL              SR299/SR399 int. antenna
         0.0   0.0   0.8   1.8   3.4   4.7   5.8   7.0   8.3   9.0   8.5   7.1   5.7   4.5   3.3   2.0   1.0   0.5   0.0
         0.0   0.0   0.8   1.8   3.4   4.7   5.8   7.0   8.3   9.0   8.5   7.1   5.7   4.5   3.3   2.0   1.0   0.5   0.0
 SR299I  L2  117.2    1.3   -3.5  IGS_01           360    05    1.0  LEICA INTERNAL              SR299/SR399 int. antenna
         0.0   0.0  -5.1  -0.8   1.4   2.5   3.8   5.0   5.3   5.0   4.5   4.2   3.6   2.6   1.5   0.8   0.4   0.2   0.0
         0.0   0.0  -5.1  -0.8   1.4   2.5   3.8   5.0   5.3   5.0   4.5   4.2   3.6   2.6   1.5   0.8   0.4   0.2   0.0
 SR299E  L1   68.5    0.5   0.1   IGS_01           360    05    1.0  LEICA EXTERNAL WITHOUT GP   SR299/SR399 ext. w/o g.p.
         0.0   0.0  -3.8   2.9   5.6   5.6   6.2   8.6  11.1  11.8  10.3   8.3   7.1   6.5   5.8   4.3   2.6   1.2   0.0
         0.0   0.0  -3.8   2.9   5.6   5.6   6.2   8.6  11.1  11.8  10.3   8.3   7.1   6.5   5.8   4.3   2.6   1.2   0.0
 SR299E  L2   52.1    0.3  -1.9   IGS_01           360    05    1.0  LEICA EXTERNAL WITHOUT GP   SR299/SR399 ext. w/o g.p.
         0.0   0.0 -12.0  -5.5  -1.2   0.6   0.9   0.9   1.0   0.6  -0.4  -1.2  -1.4  -1.1  -0.9  -0.9  -0.7  -0.2   0.0
         0.0   0.0 -12.0  -5.5  -1.2   0.6   0.9   0.9   1.0   0.6  -0.4  -1.2  -1.4  -1.1  -0.9  -0.9  -0.7  -0.2   0.0
 SR299G  L1   49.2    4.8   1.9   IGS_01           360    05    1.0  LEICA EXTERNAL WITH GP    SR299/SR399 ext. with g.p.
         0.0   0.0   1.9   1.7   2.6   3.7   4.6   5.6   6.6   6.7   5.9   4.9   4.6   4.4   3.4   1.7   0.4   0.0   0.0
         0.0   0.0   1.9   1.7   2.6   3.7   4.6   5.6   6.6   6.7   5.9   4.9   4.6   4.4   3.4   1.7   0.4   0.0   0.0
 SR299G  L2   41.8    3.4  -5.2   IGS_01           360    05    1.0  LEICA EXTERNAL WITH GP    SR299/SR399 ext. with g.p.
         0.0   0.0  -2.5  -1.8  -0.6   0.5   0.9   0.7   0.2   0.0   0.0   0.1   0.1  -0.2  -0.6  -0.8  -0.6  -0.2   0.0
         0.0   0.0  -2.5  -1.8  -0.6   0.5   0.9   0.7   0.2   0.0   0.0   0.1   0.1  -0.2  -0.6  -0.8  -0.6  -0.2   0.0
 MINXDP  L1  163.1    2.2  -8.2   IGS_01           360    05    1.0  MACROMETER     MACROMETER X-DIPOLE   Mod.4647942
         0.0   0.0 -27.0 -22.0 -15.1  -7.4   0.1   6.6  11.6  14.8  15.9  15.0  12.3   8.5   3.9  -0.3  -3.3  -3.7   0.0
         0.0   0.0 -27.0 -22.0 -15.1  -7.4   0.1   6.6  11.6  14.8  15.9  15.0  12.3   8.5   3.9  -0.3  -3.3  -3.7   0.0
 MINXDP  L2   91.3    4.3   2.0   IGS_01           360    05    1.0  MACROMETER     MACROMETER X-DIPOLE   Mod.4647942
         0.0   0.0  14.8   9.6   7.6   7.6   8.8  10.3  11.6  12.2  11.9  10.6   8.3   5.4   2.1  -0.9  -2.9  -3.0   0.0
         0.0   0.0  14.8   9.6   7.6   7.6   8.8  10.3  11.6  12.2  11.9  10.6   8.3   5.4   2.1  -0.9  -2.9  -3.0   0.0

A.7.8   References

Braun, J., C. Rocken, C. M. Meertens, and J. Johnson, GPS antenna mixing and phase center corrections, Eos Trans. AGU, 1993 Fall Meeting Supplement, p. 197, 1993.

Elosegui, P., J. L. Davis, R. T. K. Jaldehag, J. M. Johansson, A. E. Niell, and I. I. Shapiro, Goedesy using the Global Positioning System:  The effects of signal scattering on estimates of site position, Journal of Geophysical Research, 100, 9921–9934, 1995. 

Mader, G. L., and J.R. MacKay, Calibration of GPS antennas, http://www.grdl.noaa.gov/GPS/PROJECTS/ANTCAL, March, 1996. 

Niell, A. E., R. W. King, S. C. McClusky, T. A. Herring, Radome effects on GPS height measurements with choke-ring antennas, Eos Trans. AGU, Spring Meeting Supplement,  S71, 1996. 

Rocken, C., GPS antenna mixing problems, UNAVCO Memo, November 12, 1992. 

Rocken, C., and C. Meertens, Antenna phase center information, UNAVCO Memo, May 16, 1991, updated May 8, 1992. 

Rocken, C., C. Meertens, J. Braun, M. Exner, and B. Stephens, UNAVCO ARI antenna tests, October, 1995. 

Rothacher, M., S. Schaer, L. Mervart, and G. Beutler, Determination of antenna phase center variations using GPS data, paper presented at the 1995 IGS Workshop, Potsdam, May 15–17, 1995..

Rothacher, M., and G. Mader, Combination of antenna phase center offsets and variation: antenna calibration set IGS_01, anonymous ftp ubeclu.unibe.ch, June, 1996.

Schupler, B. R., and T. A. Clark, How different antennas affect the GPS observable, GPS World, November/December, 1991. 

Schupler, B., R. L. Allshouse, and T. A. Clark, GPS antennas — measurements and multipath, DOSE Investigators Working Group Meeting, October, 1992. 

Sims, M. L., Phase center variations in the TI 4100 GPS receiver system's conical spiral antenna, Proc. 1st Int. Sym. Positioning with GPS, Rockville, MD, pp. 227–244, 1985.