Abstract: An automatic antenna (100) for a portable electronic device includes a shaft (20), a hollow securing element (30), a sliding element (50) having a plurality of sliding arms (54) symmetrically disposed on an outer wall thereof, a hollow rotating element (60), a housing (80), and a spring (70) disposed between the rotating element and the housing. The securing element has a plurality of blocks (320) symmetrically disposed on an inner wall thereof. The blocks define a plurality of slots (3200) therebetween. The sliding element defines an end surface (56). The rotating element includes a peripheral cam portion (61). A plurality of projections (604) protrudes from a periphery of the cam portion. The shaft extends through the securing element, the sliding element, the rotating element, the spring, and the housing in that order. The sliding arms can slide within the slots, and the projections can slide in the slots.