CRITICAL COUPLING OF THE INVERTED-F ANTENNA BY INCREASING EFFECTIVE INDUCTANCE

Abstract

In this letter, a novel feed structure that can achieve critical coupling in a planar inverted-F antenna (PIFA) is proposed. The proposed structure considerably increases the effective inductance simply by inserting a branch capacitance between the feed line and the shorting pin of the conventional planar inverted-F antenna without structural change to the antenna or ground plane. The extremely low profile PIFA for the GSM900 band is designed to verify the proposed feed structure for critical coupling. The designed PIFA fully covers the GSM 900 band for VSWR < 3. Also, a good omnidirectional radiation pattern was obtained at its operating frequency.