The transmitted beam for typical meterological radars is not perfect - it is not a pencil beam like a laser is.
if antenna is much larger than the wavelength of the transmitted radiation, the beam is much more focussed, like a laser.
If this is not the case, you end up with
1/2 power beam width
, the power drops off by 3 dB
= 0.95° for the 88D
here is a 3-dimensional view of a real beam pattern