In this paper, a compact, low-profile, circularly polarized UHF RFID reader antenna conformal to a dielectrically controlled plastic support is proposed. The radiating element for the UHF-RFID band (865-868 MHz) has been realized through a circular array of four inverted-F monopoles, where the array elements are excited with a 90-degree phase offset (sequential rotation feeding technique) through a microstrip feeding network. To allow for a friendly prototype realization, the antenna structure is thought to be shaped on adhesive copper and the dielectric support to be 3D-printed in Poly-Lactic Acid (PLA), whose permittivity and loss tangent have been measured and taken into account in the simulation phase. A significant antenna compactness (60mm × 60mm × 6.5mm) has been obtained. Reflection coefficient, port isolation and radiation patterns are evaluated by numerical simulations.