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Proposed is a concept of a directional multi-band antenna employing frequency selective surfaces (FSSs). To confirm the feasibility of the concept, the proposal is implemented by combining a metal reflector, two FSSs that act as frequency filters, and a multi-band radiator. The proposed triple-band antenna can radiate at 800 MHz (the metal reflector or FSS 1), 2 GHz (FSS 2), and 4 GHz (FSS 3). FSS 2 passes waves at one frequency band (800 MHz) and reflects all other bands, and FSS 3 passes waves at two frequency bands (800 MHz/2 GHz) and reflects all other bands. Beam control is easy since all that is needed is to change FSS size and/or the distance between the radiator and metal reflector/FSS. Electromagnetic field simulations and measurements demonstrate good directivity in the frequency bands of 800 MHz, 2 GHz and 4 GHz.

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SUMMARY This paper proposes a sector base station antenna for mobile wireless communication systems employing multiple woodpile metamaterial reflectors and a multiband radiator that establishes the same beamwidth in the horizontal plane for more than two frequency bands. Electromagnetic Band Gap (EBG) characteristics of each metamaterial reflector can be controlled through structural parameters of the woodpile reflector, e.g., the rod width and rod spacing. As an example of the proposed antenna, a design for a triple-frequency-band antenna that radiates at 800 MHz, 2 GHz, and 4 GHz is shown. The algorithm used to adjust the beamwidth of the proposed antenna is newly introduced and adjusts the beamwidth to be the same for each band using the rod width of the woodpile. A prototype of the proposed antenna has the approximately 90 • beamwidth in the horizontal plane at the three frequencies, and the measurement results agree well with the electromagnetic field simulation results. key words: sector base station antenna, multiband antenna, metamaterial, electromagnetic band gap (EBG) characteristics

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