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Design of a microstrip-line-fed sleeve monopole antenna for broadband operation is proposed. This broadband design is achieved by properly selecting the sleeve length and the spacing between the monopole and sleeve. An important feature in the proposed design is that the impedance matching condition can be performed well even when a very small ground-plane length is used. In addition, the impedance bandwidth keeps nearly constant for the ground-plane length varied with a great range. Stable radiation patterns across the operating band are also observed.