Antenna beam width

Of course!
As rule of thumb, Theta=57*Lambda/D [deg]
More accurately Theta= k*lambda/D [rad]
where, tipically, 0.5<k<1 and depend on many factors but especially depend on the current distribution over the radiative parts.

Theta= 3 dB beamwidth
D=Diameter of the antenna
For antenna different from aperture, i.e. Yagi, find the Equivalent Area and them D=(Equivalent_Area*4*3.14...)^0.5

A more exaustive, and easy to understand treatement my be found on the Blake-Antennas, Jasik-An Introduction..., Kraus-Antennas

Note however that different size means different input impedance, so matching may be required to obtain the same sensitivity!

oh,what kind of antenna,at first it certainly have