In this chapter, the various types of circularly polarised printed antennas are first briefly introduced in Section 4.1. In Section 4.2, a simple design method for a singly-fed antenna is described together with some useful design data. This method is useful in understanding its radiation mechanism and to roughly design it. However, if the general radiation mechanism and an accurate design method are required, then the more exact treatment, developed in Section 4.3, is necessary. In Section 4.4, some considerations of mutual coupling are described.