Here are results that I obtained using a pocketVNA:
400 kHz - 3 GHz, S11:
Closer view, 1.4 GHz - 1.9 GHz, S11:
Antenna is tuned at about 1.605 GHz, which is about 63 MHz high. Maybe manufacturing variances accounts for the large variance in SNR that some are receiving (haven't been following this much lately).
1.4 GHz - 1.9 GHz, Smith chart: