Associated to an oscillator, isolators prevent frequency drift caused by waves reflected from the antenna. This advantage is specially valuable for a frequency modulated klystron.Similarly, in the case of its use on measuring bencheswhere the isolation factor of the isolator (ratio TIz/Tzl) expressed in decibels, does not need to be particularly high. From the point of view of reaction on the transmitter an isolator of 20 decibels is equivalent to an isotropic attenuator of 10 decibels but has the advantage of almost fully maintaining the power of the generator.Introduced in a delay line, isolators avoid, in traveling wave tubes, coupling between the input and output of the tube. Such coupling may arise either through a mismatch in the output guide, or through the presence of a wave whose direction of propagation is opposite to that of the circulation of energy. The use of an attenuating impedance with isotropic medium, uniformly distributed or not, can suppress spurious oscillations only at the expense of the tube efficiency and of a deterioration of the gain characteristic with frequency. The use of an isolator, comprising an anisotropic body in the delay line, avoids these disadvantages. Summay-A model of one-way transmission of microwave electromagnetic signals over the ocean surface is developed from experiment. The received signal is described as a vector s u m of a constant direct signal, a coherent reflected signal, whose amplitude and phase are fczed by geometry and sea state, and a fluctuating reflected component of random amplitude and phase. By interpreting experimental data in the light of this phenomenological model it has been possible to relate, quantitatively, the coherent and incoherent reflected signal and total signal to geometry and sea state. The results give support to the theoretical expression previously derived by Ament and others relating the coherent reflected signal to "apparent ocean roughness."In addition, the general shape of the curve relating the incoherent scattering to "apparent ocean roughness'' has been established and its asymptotic value found.
Simultaneous measurements of refractive index and radar reflectivity have been made in the clear atmosphere. The theoretical relationship between the refractive index spectrum and reflectivity de· scribed by Tatarski was used to compute reflectivity from the refractive index data. Excellent agree· ment is shown between the computed and measured reflectivity. These results indicate, (1) reflections from the clear atmosphere can be described quantitatively in terms of the refractivity spectrum, and (2) the -j refractivity spectrum well represents the atmosphere for these data out to limiting micro· scales smaller than 5 em.
The possible use of multiple wavelength radar systems to determine raindrop size distributions is examined. Pairs of radars at 1, 3, and 10 cm, respectively, are considered; the method involves measurements of rain reflectivities at two wavelength and at two range intervals separated by about one km. Assuming a general exponential form for the drop distribution, equations are derived relating the distribution parameters to the measurements. From these analytical forms the sensitivities of these parameters to radar inaccuracies are examined. The results show that one needs combined 2‐radar accuracies of 1 dB to get even marginal drop distribution accuracies. Such accuracies are considered impractical at present. Other impractical constraints implicit in the results are the assumed uniformity of reflectivity over distances of approximately 1 km, and the requirement to average as many as 104 independent power samples.
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