Compact Two-Inverted-F-Antenna System With Highly Integrated $\pi$ -Shaped Decoupling Structure

Conventional decoupling technique uses the resonatorbased grounded structure that separates two antennas at a distance for improving port-to-port isolation. The decoupling structure usually requires certain space, which increases the overall antenna size. In this communication, a small π-shaped structure that can be highly integrated into a very compact two-inverted-F-antenna (IFA) system is presented. The two-IFA design occupies a size of 5 mm × 38 mm (about 0.04λ× 0.30λ at 2.4 GHz) with two symmetrical IFAs facing each other by a gap of 2 mm only. Each IFA is capable of covering the 2.4 GHz (2400-2484 MHz) and 5 GHz (5150-5825 MHz) wireless local area network (WLAN) bands. The π-shaped decoupling structure is encircled by the IFAs and comprises two shunt capacitors and a series inductor. By properly selecting the capacitance and the inductance, the isolation between the IFAs in 2.4 GHz band can be largely enhanced. In addition, because of current null arrangements of the 5 GHz band, the proposed design is inherently decoupled over the higher band. The results show that good isolation >16 dB over the 2.4 and 5 GHz bands can be attained. It is also noted that the decoupling bandwidth of the present decoupling structure is narrow.