Truncated corner patch antenna

Can someone explain the theory why truncated corner can give circular polarization?

Anyone knows any articels or books there I can read about it?

Because by breaking the symmetry of the patch antenna, you excite an orthogonal mode. By properly adjusting the dimensions you can have the two modes with equal amplitude and a phase difference of 90o. Therefore, you get circular polarization.

See for example:

Microstrip Antenna Design Handbook (ch. 8)
Authors: Garg, Bhartia, Bahl, Ittipiboon
Artech House, 2001

Handbook of Microstrip Antennas (ch. 4)
Authors: James and Hall (Ed.)
Peter Peregrinus - IEEE, 1989

Regards

Z