How is GPS Antenna LNA Gain Referenced?

GPS antenna LNA gain values are not referenced to anything. Its a measure of RF signal amplification only and is expressed in terms of "dB". NovAtel's GPS antenna data sheets provide antenna element gain versus elevation angle which is referenced to an isotropic antenna for Right Hand Circularly (RHCP) polarized signals and therefore its gain is expressed in terms of "dBic". So, for example, if the LNA has 27 dB of gain, this means all satellites will be amplified by the same amount (27 dB) regardless of their elevation angle. The antenna element, on the other hand, will provide different gain for each satellite. For example, at an elevation angle of 90 deg (zenith - boresight) the antenna element will amplify GPS signal by at least 5 dB with respect to isotropic antenna (+5 dBic). Thus, total gain for this satellite will +5+27=32 dB. On the horizon (elevation angle of zero), the total gain will be less, since antenna element gain is much lower. This is by design, to amplify high elevation signals, and to attenuate low elevation signals which are more prone to adverse multipath effects.