In this paper, a new design approach is presented for achieving a miniaturized quad-band microstrip patch antenna (MPA) suitable to be used for 915-MHz (UHF band), 2.45- and 5.8-GHz (ISM band), and 3.5-GHz (WiMAX band). The proposed antenna is called modified square spiral antenna (MSSA) which is composed of a modified dual-arm square spiral patch strip structure and a tapered-ground plane with coplanar wave-guide (CPW)-fed configuration to feed this antenna, all printed on the top side of an FR4 substrate. The proposed antenna is designed through intermediate systematic design steps of antennas starting from a conventional strip-fed rectangular MPA and ending by achieving MSSA. A CST Microwave Studio (CST MWS) is used to model the designed antenna and simulation results, in terms of return loss (S11), realized peak gain and efficiency, besides to radiation patterns, are obtained. To validate the design concept, the antenna structure is fabricated, and the simulated and measured S11 results nearly coincid with each other. The proposed antenna is characterized by miniaturized size of 28×28 mm2, and based on measured -10-dB S11 result, MSSA has four bands, band 1: 915-GHz (872-929 MHz), band 2: 2.45-GHz (2395-2510 MHz), band 3: 3.5-GHz (3470-3550 MHz), and band 4: 5.8-GHz (5698-5900 MHz).
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