Characterizing a Ka-Band FMCW Reflectometer

Abstract

A Ka-Band ultra-fast, ultra-wide band Frequency Modulated Continuous Wave (FMCW) reflectometer to measure the plasma density profile has been designed and developed at Institute for Plasma Research (IPR). We present here the need for ultra-fast and ultra-wide frequency of operation and estimate expected beat frequencies for the instrument. Three distinct corrections are made to the obtained frequencies. Firstly, inherent non-linearity of the frequency source is removed by shifting non-linearity to the tuning voltage of the hyper-abrupt varactor tuned oscillator and then correcting mismatch of the absolute values of frequency by introducing a delay line to account for the difference in length between active and reference paths for producing the beat frequencies. Using code developed based on the short time Fourier transform we extract the beat frequency to measure various known distances and verify with our beat frequency estimations and also show that range resolution obtained is very close to the theoretical one obtained.