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.
Summq-Using methods of physical optics, a statistical description of the scattering of waves off a rough surface is obtained. The rough surface is assumed to consist of a large number of independent point scatterers which fluctuate randomly in vertical position and also disappear and appear at random. The surface is divided into cells so that no more than one scatterer can occupy a cell, and the events in any two different cells are independent of each other. The average scattered signal, the mean square fluctuation, and the time covariance of the fluctuating portion of the signal are computed in terms of the mean-square scatterer height, the grazing angle, the radiation wavelength, the decay time for disappearance of scatterers, the time autocorrelation of a scatterer height, and the a priori probability of finding a given cell occupied by a scatterer.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.