Freq            - Operating Frequency

Gain_Linear    -  Antenna Gain

AF               -   Antenna Factor

Antenna Gain is described by the amount of power that is transmitted in the direction of peak radiation to that of an isotropic source. Antenna gain is more commonly quoted than directivity in an antenna's specification sheet because it takes into account the actual losses that occur. It is commonly denoted in decibels(dB) but can be also represented in numeric terms as given in the above calculator. 

Antenna factor defines the relationship between the electric field strength E, around the antenna and the voltage output of the antenna V. To be more precise, in numeric terms, it is the ratio of the electric field strength E to the voltage V, induced across the antenna output terminals. Its units are volts/meter or microvolts per meter. The antenna factors are generally expressed in dB microvolts per meter.