Aircraft scintillation spectra

Using the model of aircraft reflection developed by DeLano, the spectra of the reflection signals are found. Spectra for the amplitude of the rectified return, for the angular fluctuation signal associated with a fixed radar line-of-sight (effective radar center fluctuation), and for the angular fluctuation signal associated with a zero time constant servo (apparent radar center fluctuation) are derived. Several types of target motion are considered: uniform rotation, random rotation, and rectilinear velocity toward the radar itself. Each of these motions produces a characteristic spectrum and the properties of these spectra are pointed out and their significance in radar system design emphasized. In particular, the importance of the spectral density at zero frequency of the apparent radar center is shown in relation to systems using very rapid automatic gain control (AGC). It is shown that such use of very fast AGC may increase this noise density by a factor of approximately three, and thus increase the system noise.