Slot antennas, with and without resistive covering, dipole antennas having a screen have been modeled by finite difference scheme in time domain. The following characteristics has been studied: 'front to back' ratio, field patterns for pulse radiation, coupling between transmitting and receiving antennas. An influence of the spacing between the antennas and the ground surface for soils having various dielectric constant and conductivity was studied. Optimal conductivity of the resistive covering have been found for various types of the covering of the slot antennas. Filling of the spacing between the antenna and the ground by the resistive material leads to large increase of the front to back ratio, the optimal conductivity depends on the spacing. When the antenna is covered on lateral sides, the optimal conductivity is greater. Partial filling of the spacing leads to moderate increase of the front to back ratio. Dipole antenna with a screen and resistive material between the dipole and the screen, placed at some height above the ground, provides greater front to back ratio, than the slot antenna, having the same size. Computed field patterns and other characteristics enable to understand behavior of the radiation of the antennas and are useful in designing of shielded antennas.