A Compact Interdigital Capacitor-Inserted Multiband Antenna for Wireless Communication Applications

A compact coupled-fed antenna for multiband wireless communications is developed in this letter. It makes use of an interdigital capacitor for impedance matching at the frequency of 1.28 GHz. To improve its impedance-matching characteristics at 2.7and 5.5-GHz bands, step-impedance transmission lines are implemented into its design. With overall optimization, such an antenna can operate at 1.26-1.3, 2.49-2.92, and 5.04-6.0 GHz, respectively, with the return loss of better than 10 dB. The two upper bands are wide enough for both applications of WiMAX (2.49-2.69 GHz) and WLAN (5-5.9 GHz). The size of the antenna prototype is only about 0.1 λ
₀
× 0.0036λ
₀
× 0.0034λ
₀
at 1.28 GHz, with almost unchanged radiation patterns achieved at each operating band.