what is the expression for front to back?

what is the expression for front to back

let say : 0° is the boresight 180° is the front to back,

but from what degree we can call the term front to back
(from 90°,145?)?

is there any book that determine the expression ?

thnks

anyone have any idea?

Front to back ratio is 0° compared to 180°. To see how this changes with the elevation /azimuth angle, a radiation diagram is usually provided.

thanks for your answer ,
but what i ment is the point that i can define the FRONT TO BACK ( TBD ).
145°,160 OR..........

THANKS