Fortran computer subroutines have been developed for machine plotting of radar or radio vertical-plane coverage diagrams for the case of interference between direct and sea-reflected waves. One set of subroutines plots detection or constant-signal-level contours on a range-height-angle chart. A second set plots signal level in decibels as a function of range for a target at a fixed (low) altitude. The first type of plot is valid for antenna heights that are within a few hundred feet of the water and for targets that are at much higher altitudes and not too close to the horizon. The second type is valid for antenna and target heights that are both less than a few thousand feet altitude, with no restriction on minimum altitude. Normal atmospheric refraction is taken into account, but scattering and ducting are assumed to be of negligible effect. The frequency range considered is from about 100 MHz to 10 GHz. The factors taken into account are frequency, antenna and target heights, antenna beamwidth, tilt of the beam with respect to the horizon, roughness of the sea (wave height), polarization of the radio waves, and the calculated or assumed free-space range. Sample plots are shown and discussed. The plotting techniques employed are briefly described, and listings of the essential Fortran subroutines are given in an appendix. (Author)
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