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The goal of this letter is to design a compact, planar UHF antenna operating over the frequency range 420Â¿450 MHz. A microstrip patch antenna is selected as the elementary radiating structure because it has a low profile and is simple to fabricate. Compact size and enhanced bandwidth are simultaneously achieved through the use of a reactive impedance surface (RIS) in place of a PEC ground plane. The inherently limited bandwidth of the patch is overcome by incorporating a U-shape resonant slot radiator within the patch area. The design, fabrication, and measurement results are presented. It is shown that a patch with a U-shape slot whose dimensions are only $0.136~lambda times 0.228~lambda$ at the lowest frequency of operation can provide more than 20% bandwidth, covering a frequency range of 410Â¿485 MHz.