In a wireless communication system, the radio propagation channel is a complicated component to characterise. Channel sounding equipment thus has to meet specific criteria to extract the desired channel parameters. In this study, the authors outline the development and validation of a vector network analyser (VNA) based channel sounder for the frequency range from 1 to 50 GHz using radio-over-fibre techniques. Three methods of de-embedding phase errors due to hardware impairments are demonstrated and validated via back-to-back measurements. The bidirectional scheme utilising optical circulators is shown to have a superior performance over the two-branch unidirectional and the two-branch bidirectional schemes. Therefore, the bidirectional scheme utilising optical circulators is proposed to achieve a long-range ultra-channel sounder based on the VNA.