Radar altimeter has become one of the most useful microwave sensing instruments for observing theearth in the past three decades, and the results from several successful missions, such as Geosat、ERS1+2 andTopex,has been widely used in many geodesy field, particularly in ocean topography. Error analysis is one ofthe core techniques in the design of Spaceborne Radar Altimeter, because the altimeter data may be impracticalfor some application cases without adequate precision. Amplitude and phase ripples of the RF system are impor-tant error sources in height measurement. This paper deals with the error issue with the help of the well-estab-lished tool——“paired-echo theory”. Firstly, we consider that the ripples have the sinusoid forms, and then wecan convert these ripples into range side lobes. On the other hand, we establish the form of the side lobe andderive the relationship between side lobes and height bias. In this way we can establish the relationship betweenamplitude (phase) ripples and height bias. And finally, applying this method to a practical system, we can getsome quantitative requirements for the amplitude and phase ripples. These requirements are very critical inradar altimeter design.