Derived from an early National Bureau of Standards (NBS) tropospheric transhorizon propaption data base [I), a particular loss term defined as path attenuation was used in the radar equation to estimate the behavior of signal-to-noise ratio with frequency (10 to 1000 MHz) and distance (SO to 1000 km) including median and I, 10, 90, 99 percent variability. This loss term depends on frequency, distance, climate, r~fractivity and an empirically derived attenuation function which takes into account effects of antenna heights. Equivalent antenna temperatures are assumed to be due to plactic noise. Receiver noise is characterized by noise figure. For conveniently chosen system parameters (I MW transmitter power, I Hz receiver bandwidth, antenn;~ gains G, = G, = 1000), signal-to-noise ratio behavior is illustrated for several target cross sections (e.g. resonant dipole, conducting sphere) as a function of frequency, distance, variability for particular climates. Conversion to other system parameter values is straightforward. The complete details are available from the author [2].
Abrtmct-Theprinciples of operation and rpphtions of frequency SeJeCtrre limitenr (FSL's) are -b e d . The d o u s typea of FSL's are g m a w into three main cl.sses: a) PSL's using multiple t a n 4 LC-resonurt circuits, each contdning two brCk-t&ck diodes; b) FSLs usiug direct signal & s o r p t i o n ; and c) FSL'r using panmetric arbhumonic generation. The theory of operption d these devices is reviewed. From the d t s , it b noted that the Churcteristicd of existing PSL's are attractive for their use in communiation systems where signal interference is a serious problem to overcome.
The propagation of electromagnetic waves in media with various horizontal layers has been analyzed. The electromagnetic fields outside the source region were obtained from the dyadic Green's functions for the case of media with three and four layers and for horizontal and vertical electric dipoles. These results agree with those obtained using Hertz potentials. One of the major results is a generalization of the dyadic Green's functions for solving the problem of media with N horizontal layers.
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