A theoretical and experimental study of angular scintillations in earth space paths

The theoretical framework and experimental results of an antenna offsetting technique which has been used to investigate angle of arrival fluctuations in the microwave region for medium (
30\deg
) and low elevation (
9\deg
) angles is presented. The receiver antenna is depointed by a small angle and the antenna gain slope in dB/deg transforms angle fluctuations into amplitude fluctuations. The sensitivity and resolution of the apparatus together with the limitations due to amplitude scintillations, their time variability, and the noise floor of the system are discussed in detail. Experimental results are presented and compared with the theory developed in the paper. The study reveals that the important parameter is the product
C^{2}_{n}L
and values are presented and discussed. The experimental values for the root mean square (rms) angular deviation
\sigma(\theta)
and of the spectral density
W_{\theta}(f)
show a great variability between day and night and between winter and summer with values of
\sigma(\theta)
ranging from below 1 mdeg up to 20 mdeg. Low elevation studies at
9\deg
indicate angular scintillations less intense than expected, and never exceeding 4 mdeg.