Improved Frequency Estimation Technique for FMCW Radar Altimeters

Radar altimeters (RA) are an integral part of aerospace navigation system because of their ability to measure height above the earth's surface with high level of accuracy and integrity. For lower altitude measurements, Frequency Modulated Continuous Wave (FMCW) radar is the most suitable choice for RA, compared to pulsed radar. The altitude measurement in FMCW-RA is carried out with the help of beat signal that captures the frequency difference between the transmitted signal and the ground reflected signal. The accuracy of altitude measurement depends on the estimation accuracy of beat frequency from the received signal. This paper proposes a beat frequency estimation technique with improved accuracy which combines FFT with Chirp Z transform (CZT) and Candan estimator. The performance of the proposed technique evaluated in terms of RMSE (Root Mean Square Error) is found to be better when compared to the existing techniques.