A Small Dual-Band Inverted-F Antenna With a Twisted Line

A twisted-line inverted-F antenna (IFA) is proposed for dual-band applications. The antenna features a twisted line for dual bands and a parasitic line for additional resonance. The twisted-line IFA has wideband characteristics in the high frequency band due to the mergence of the resonances of the twisted line and the parasitic line. The electric size of the antenna is 0.109 lambda x 0.025 lambda x 0.0025 lambda, and its length is about 44% that of a conventional IFA. The twisted-line IFA was fabricated on a thin FR4 substrate, and its performance was measured. The antenna operates at 930 MHz with a bandwidth of 30 MHz, and at 1.7 GHz with a bandwidth of 350 MHz for S11 less than -6 dB; the maximum radiation efficiencies were 48% at 937 MHz and 80% at 1.645 GHz.