acceptable side lobes and back lobe levels in derective antennas

hello
plz tell me what should be the acceptable back lobe and side lobe level in dB scale,if my main lobe is at 15 dB?
noor

Why do you think that we know your design requirements?

there isn't any general value for that.

it depends on the requirements of your application (if you are a user) or the specification asked by a client (if you are a manufacturer)

Antenna stray lobes depend on desired interference levels required for directivity reception or transmission.

15 dBi peak with 0dBi lobes may be adequate for some applications but for a RADAR signal it might need to be -40dBi depending on dynamic range of signals.

thank you so much...
stay blessed... :)