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A log-spiral antenna is described. It is part of the ultra-wideband stepped frequency ground penetrating radar (GPR) for subsurface landmine detection currently being developed at the University of Manitoba. Log-spiral antennas possess many features that are desirable in such a radar system: low profile, high bandwidth, and circular polarization. The design and construction of the antenna are described. The antenna is fitted with a wideband balun to balance the current between the two arms of the spiral. An absorber loaded cavity is used behind the antenna to help direct the energy into the ground and keep it from radiating into the air. A study of the far and near fields of the antenna, via simulations and measurements, is presented. The near fields are measured using short coaxial E-field probes at an electrically short distances from the antenna and agree well with simulations.