Method of Isolating and Tuning the Two Dominant Modes of a Printed Inverted-F Antenna

Abstract

A systematic method for decoupling and increasing the tunability of the first and third-order resonant modes of a compact, printed inverted-F antenna is presented. By identifying and utilizing surface-current symmetry in the third mode of a single-meander structure, a branch substitution is performed to support a new resonant boundary condition and allow independent tuning of the third mode. This allows a third-to-first-order harmonic frequency ratio of less than 3:1 to be achieved, with simple design equations presented to provide the antenna designer with flexibility for targeting certain bands. The methodology is further validated by incorporating two such branches and a ground slot to demonstrate a multiband inverted-F antenna targeting typical cellular and wireless bands (GSM-900, UMTS-2100 and WLAN-2.4 GHz). The 65×110 mm manufactured antenna exhibits better than -6 dB [S11] from 880-1000 MHz, 1920-1980 MHz, and 2060-2640 MHz, with measured radiation efficiencies in the range of 72 to 93%. The close agreement between simulation and measurement demonstrates the suitability of the design methodology for use in compact, multiband antenna designs for personal communication devices.