The design and characterization of a compact ultrawideband (UWB) antenna is presented in this letter. The bases for achieving such an UWB operation are through using semicircular microstrip monopole antenna and introducing a metamaterial as an artificial magnetic conductor (AMC). The AMC reduced antenna size, enhanced antenna gain and bandwidth, and decreased the cross-polarization effect. A spiral artificial magnetic conductor (SAMC) is used as a ground plane with one and four arms to further improve the antenna performance. Furthermore, to reduce surface wave propagation and decrease bandwidth discontinuity, holes surrounding the antenna structure are drilled in the substrate. The new antenna provides an impedance bandwidth of more than 35 GHz with S11 < -10 ?? 0.5 dB. The SAMC antenna has a wide frequency range for practical applications ranging from all required wireless communication bands, i.e., GSM 900 MHz, ISM band, Bluetooth, wireless LAN and S-band, to new medical applications. Details of the proposed antenna design are described, and experimental results are presented.