ABSTRACT A circularly polarized (CP) helix antenna with conical radiation pattern operating in Global Positioning System L5 (1.176 GHz) and L1 (1.575 GHz) bands is proposed. Adopting helix arm nesting technique, the proposed antenna is equipped with two tapered helix radiation arms, namely, outer tapered helix arm and inner tapered helix arm, which are operated in L5 and L1 bands, respectively. Two ports are designed to excite the two tapered helix arms. The antenna can operate at L5 and L1 band