Radar altimeters selects full-deramp technology in pulse compression, and apply two frequencies to reduce the ionospheric range errors. These will, as this paper shows, introduce an effect called “Ionospheric Dispersion”, especially in lower frequency, and this can lead to errors in height estimation. No foreign document is accessible to solve this problem, so this paper attempts to illustrate it. The authors at last draw the conclusion that these errors can be treated similarly as the quadratic phase errors, whose nature and solution are well-established, and they also discussed the magnitude of this error for a typical altimeter. Furthermore, the actual Doppler errors are deduced are it is shown that the existent Doppler algorithms are adequately accurate. Finally, by computer simulation, the sidelobes introduced to the system point target response are illustrated and the errors are estimated.