A Compact Frequency-Reconfigurable Antenna With Independent Tuning for Hand-Held Wireless Devices

This communication presents the design of a compact loop antenna with independent frequency tuning. The proposed antenna consists of a feed line fed by a <inline-formula> <tex-math notation="LaTeX">$50~\Omega $ </tex-math></inline-formula> coaxial probe and four resonating arms on the adjacent sides of the feed line. The two outer resonating arms are directly coupled to the feed line and the other two inner resonating arms are coupled to the outer arms. The proposed antenna has a footprint of 25 mm <inline-formula> <tex-math notation="LaTeX">$\times 10$ </tex-math></inline-formula> mm <inline-formula> <tex-math notation="LaTeX">$\times0.2$ </tex-math></inline-formula> mm. The designed antenna operates at 0.9, 2.4, 3.5, and 5.5 GHz. Each of these bands is individually tuned using varactor diodes. Thus, the aggregation of these tunable bands provides wide bandwidth. The impedance bandwidth and percentage bandwidth of the antenna are 270/1000/400/700 MHz and 33%/47.6%/11%/12.7%, respectively. Furthermore, the gain and efficiency of the antenna are 1.7/1.3/2.1/2 dBi and 60%/63%/65%/69%, respectively. The prototype antenna is fabricated and tested. The measured impedance and radiation characteristics of the antenna are in good correlation with the simulation results.