A multiband printed inverted-F antenna using current symmetry

A compact multiband antenna is presented, which consists of a planar inverted-F structure with two branches placed at key locations along the main radiating arm, and a microstrip-coupled slot in the ground plane. A systematic method for decoupling and increasing the tunability of the first and third-order resonant modes of the inverted-F antenna is applied. By identifying and utilizing surface-current symmetry in the third mode of a single-meander structure, a branch substitution is performed, thus enabling independent tuning of the third mode. This allows a third-to-first-order harmonic frequency ratio of less than 3:1 to be achieved. By incorporating two such branches on the main radiating arm, three separate electric resonances in the 920MHz, 1950MHz, and 2450MHz bands are achieved, while an additional complementary magnetic resonance is introduced at 2150MHz by adding a slot to the ground plane.