Isolation improvement of WLAN internal laptop computer antennas using dual-band strip resonator

A high-isolation two-antenna structure comprising two small-size uniplanar WLAN antennas and a dual-band strip resonator embedded in-between for laptop computer application is presented. The proposed design occupies a small planar size of 9 × 50 mm² when mounted above the top edge of the large supporting metal frame of the laptop display. The two WLAN antennas are coupled-fed printed PIFAs capable of covering 2.4/5.2/5.8 GHz band operation, each occupying a size of 9 × 13 mm² and both facing to each other back-to-back with a spacing of 24 mm (that is, the total length of the proposed two-antenna structure is 50 mm). The embedded strip resonator functions as a dual-band wavetrap over the 2.4 and 5.2/5.8 GHz bands to trap the antenna´s near-field radiation between the two antennas, which effectively reduces the mutual coupling between the two antennas. Good measured isolation (S₂₁ < -18 dB) over the 2.4/5.2/5.8 GHz bands is obtained, which is acceptable for practical laptop computer applications. The proposed design works for the large groundplane condition in the laptop computer, different from many of the reported two-antenna designs working for the relatively much smaller groundplane conditions such as in the mobile phones and PC cards.