How to reduce the Quasi yagi antenna and the printed dipole Antenna's beamwidth

hi all:
I designed a Quasi-Yagi antenna and a printed dipole element,but the beamwidth is wider than 150,and I wonder how can reduce the beamwidth under 100. Does anyone knows which paremeter influence the beamwidth.Thanks

In Yagi-Uda antennas, the gain and beam width are functions of antenna length.

The beam width of 150 degrees is quite poor; it is similar to a bare dipole. You can add a flat reflector or a corner reflector to reduce is below 100 degrees.

Thanks,it is helpful.