Modern spaceborne precision radar altimeters transmit radio signals of a spectrum bandwidth up to 300 MHz, but the bandwidth should be still increased for precise estimation of the roughness of the sea surface. In this research, the influence of the ionosphere on wideband radar signals is investigated and then it is shown that the signals are strongly influenced by the dispersive distortions in the atmosphere of the Earth even in Ku-band. Finally, the allowable bandwidth of a space borne precision radar altimeter signals is estimated, at which we could ignore the presence of these distortions.