If you have an antenna with calibration data, chances are it includes a number of columns of data. One column should be the frequency being tested. The others can include free-range performance, gain, and more.
Here is an example of antenna correction data from a German antenna manufacturer:
The most useful entry is the AF, or antenna factor data. This data has positive values and typically has units of dB/m (decibels per meter) and can be directly entered into a spectrum analyzers correction table. This data mathematically corrects the incoming data and “removes” the antenna characteristics from the measurement.