What are the common techniques for narrowing the main lobe and reducing the sidelobe of array antenna ~ ~ ~

There is a limit to reducing the beam width under a certain aperture. You can optimize array elements. Of course, it is also useful to select an array element. The key is to see how far you narrow the beam. For example, it is often difficult to reduce a light beam from 6 degrees to 2 degrees or 3 degrees. Generally speaking, it is also helpful to choose specific materials or structural designs. Sidelobes, in general, are pattern synthesis. Generally, it is not a big problem for an array antenna to reach -30db, but if you want to reach -40 or -50, it depends on your antenna form or the degree of antenna synthesis.