Displacement of phase centre location of a tri-mode stacked circular microstrip patch antenna

The global phase centre and cross polarization of a multi-mode stacked circular microstrip antenna are studied when the first three modes, TM₁₁, TM₂₁ and TM₀₂, are excited. These properties can be controlled by amplitude and phase excitations of each individual mode. It will be demonstrated that such antennas represent virtual array antennas by having a broadside amplitude patterns at the far-field region while their effective source of radiation are displaced from their physical center. Consequently, the resulting antenna becomes equivalent to multiple antennas. In addition, it will be shown that the third higher order TM₀₂ mode provides an option to minimize the antenna cross polarization level over the boresight angle.