Patch antenna center grounded with ferrite rings

I have encountered a 3x4 rectangular patch antenna array that has some patches center grounded with ferrite rings at only 4 corner patches. The rest are just regular pathces.

The ferrite beads should create certain inductance.

All patches (including centered grounded ones) have the same size and are end fed on the same edge.

Its peak gain is about 18dBi.

Does anybody know the reasons for adding 4 patched center grounded with ferrite rings?

Your help will be greatly appreciated.

Apparently it's a means to achieve the intended directivity by manipulating the phase and/or magnitude of the respective patches feeding. I guess, you won't be able to predict the effect without an exact EM simulation. Or you find the topology described in literature.