To prevent interference between ultrawideband (UWB) systems and existing wireless systems, creating notches in the UWB radiated field spectrum has been proposed. This filtering effect can be achieved by integrating a slot resonator to a UWB antenna. However, in printed monopole or dipole type UWB antennas, the notch frequency of the embedded slot depends on substrate and slot parameters. In this paper, we present a method to calculate, very accurately and efficiently, the notch frequency of such antennas. This method is validated by comparing theoretical and experimental results for 19 different slot width, slot length and dielectric constant combinations. The average difference is about 2%. We also assess the filtering action of slots from two aspects: the mismatch loss at the input and the radiation level in the far field. The sensitivity of the notch frequency to antenna parameters is also investigated.