A multi-mode, multi-band antenna system for a handheld wireless device includes a Quadrafilar Helix Antenna (QHA) that radiates circularly polarized waves is fed by a co-axial cable. The co-axial cable is also used in combination with the QHA as a monopole antenna. Because of the distinct electromagnetic field patterns of the QHA versus the combination of the QHA and the co-axial cable operating as a monopole antenna, the cross coupling between the two modes is low. In certain embodiments the co-axial cable can itself be formed into a helix in order to reduce the physical length of the antenna system while maintaining an electrical length desired to supported certain frequency bands in the monopole mode. According to certain embodiments a post which also serves to increase the effective electric length of the co-axial cable and thereby support a lower frequency band is provided along the centerline of the QHA.