Single patch antenna generating electromagnetic field with orbital angular momentum

We investigate on the possibility to generate an electromagnetic field with a non-zero orbital angular momentum (OAM) using a single patch antenna. First, we report an analytical study of a circular patch antenna in order to show that a circular polarized TM_nm mode generates an OAM of order n - 1. Then, we design an elliptical patch antenna that radiates a circular polarized electromagnetic field with OAM of the first order. The analysis of the proposed antenna is supported by a proper set of full-wave numerical simulations.