## Rand Memoranda, Issue 4949 |

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1/2 wavelength ACTUAL ANTENNA Aeronautics and Space altitude h angle 58 antenna pattern antenna-ionosphere system cone critical fre critical frequency decreases density is greatest determined from Eq directional antenna dropped to half earth effective antenna gain effective directivity effective gain drops effective sensiti energy density f COS q F layer field of view found from Eq free electrons frequency f frequency of 1.3 frequency of observation frequency the effective gives h VTL half its maximum horizontal distance ionospheric electron density isotropic antenna looking limit the field line in Fig little to limit low-frequency system maximum value National Aeronautics nearly isotropic antenna observed frequency path penetrate the ionosphere plane plasma frequency qualitatively correct quency radio frequency signals ratio ray reaches recombination region satellite whose orientation scale height second ray sin2 solid angle Space Administration thunderstorms twice the critical two-element broadside array value of f/fc value of g vertical