| It has been found that reflections of considerable importance to the propagation of ultra high frequency radio waves occur commonly within the troposphere. It is believed that these tropospheric reflections are caused by weak irregularities in the dielectric constant of the air. Few attempts have been made to understand the physical processes that lead to these irregularities. One of these is the study of microwave radar "angels" (i.e. the reflection of radio waves from a sensibly clear region of the troposphere).;A microwave radar at 10,000 Mc/sec. was constructed for this purpose. By using separate transmitter and receiver antennas, measurements were taken in the near field to provide a high degree of sensitivity in Gamma 2. From theory, it is found that the difference between the signals scattered from flat dielectric and conducting laminas of like geometry is the difference in Gamma2 when the width of the lamina is less than the diameter of the Fresnel zone. Measurements were made on signals scattered by glass and brass discs as a test of this principle. From this information it was found that Gamma2 for a glass disc of thickness 0.94 cm. and dielectric constant 6.71 is equal to 0.43 +/- .05, in close agreement with the theoretical value.;One aspect of the study of microwave angels in the analysis of the plane-wave power reflection coefficients (Gamma2) of dielectric lamina. Such lamina would represent layer-type irregularities in refractivity of the troposphere. |
