An antenna, especially for use with a handheld RFID reader for scanning RFID tags oriented in different orientations, includes a feeding port located on an axis for supplying an RF signal to a primary antenna member for transmitting and receiving electromagnetic waves. A secondary antenna member is juxtaposed with the primary antenna member for re-radiating the electromagnetic waves propagated by the primary antenna member. Each antenna member includes one antenna element extending in a radial direction away from the axis and continuing along at least one turn in a turning direction at least partly about the axis, and another antenna element extending in an opposite radial direction away from the axis and continuing along at least one turn in the turning direction at least partly about the axis. The electromagnetic waves have congruent slant polarizations each having components in both of two mutually orthogonal planes to read the tags.