The response of microwave reflectometry under generalized configuration

The response of microwave reflectometry for various configurations is studied theoretically. Based on the Kirchhoff integral (i.e. physical optics), analytic formulae for the measured electric field are obtained. Phase and power sensitivities for weak fluctuations are derived. It was found that the effective spot size, which is a combination of the real spot size and the Fresnel zone, of the launching and the receiving beams is an important parameter, determining the sensitivities. Fringe jump and phase runaway phenomena are attributed to two parameters: one is proportional to the normalized wavenumber of the fluctuations, and the other is proportional to the plasma shift (i.e. misalignment). In the case of frozen turbulence, a complex power spectrum of the measured field becomes a universal quantity, because of easy correction of the configuration effect. Using this feature, an ideal complex amplitude signal (i.e. free from diffraction effects) can be reconstructed.