Abstract-A novel antenna configuration for quad-band operation is presented. The quad-band antenna has a directional radiation pattern in four frequency bands, i.e., B1 (800-900 MHz), B2 (1.7-2.5 GHz), B3 (3.3-3.6 GHz), and B4 (5.1-5.9 GHz), covering all spectrums for existing wireless applications, such as GSM, PCS, WCDMA, WiFi, and WiMax. The operating frequency of the quad-band antenna can be adjusted by the use of a MEMS switch, making it suitable for cognitive radio applications. First a switchable quad-band antenna element is introduced. Then a two-element antenna array is developed to increase the antenna gain for base station applications featuring a gain value of about 9-11 dBi over all four frequency bands.Index Terms-Base station antenna, cognitive radio, quad-band antenna, switchable antenna.

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