This letter describes a design of an internal quad-band antenna resonating at Cellular (824 894 MHz), DCS/PCS (1710 1880 MHz/1850 1990 MHz), and WiBro (Wireless Broadband Internet, 2300 2390 MHzs) system band by inserting the spiral slits corresponding to the resonant frequencies. In order to accomplish this goal, double-spiral structures are suggested and analyzed by using a commercially available software package based on the finite-difference time-domain (FDTD) algorithm and basic equation for fundamental resonant frequency. In addition to that, the experimental results are compared with the predicted data obtained from the software package, CST MW Studio by considering the criterion of VSWR as 3:1. The proposed antenna and substrate are so small that they can be mounted and packaged in mobile phones. The measured radiation patterns are in good agreement with simulated results.

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