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A simple but efficient feed structure for achieving a wide-impedance bandwidth is proposed. The feed structure operating as a parallel resonance circuit can provide controllable resonance additionally in the conventional planar-inverted-F antenna (PIFA). It was verified that the modified PIFA incorporating the proposed feed fully covers Long Term Evolution (LTE) 13, Global System for Mobile Communications (GSM) 850 and 900 bands under VSWR 3:1 with good radiation patterns.
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Jeon et al. (2011) studied this question.
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