Control of phase center and polarization in circular microstrip antennas

In this paper, the problem is investigated in a more general form, involving phase center location and polarization of multimode, multilayer, circular microstrip antennas. It is shown that, these parameters can be controlled by amplitude and phase excitations of the modes, in particular, when the first three modes are being excited, which are the TM₁₁, TM₂₁ and TM₀₂. It is also shown that, the phase center of such antennas can be changed, while maintaining the main beam direction constant, thus, introducing the concept of virtual antennas