A Very - Low - Frequency Antenna for Investigating the Iono - sphere With Horizontally Polarized Radio Waves

The advantages of a horizontal half-wave resonant antenna f or very-low-frequency propagation experiments lie in its r elatively simple and inexpensivc construction and in its radiation pattern which is maximum in the vertical direction. The radiation fields of this type of antenna located at the s urface of a condu cting earth consist of: 1, A horizontally polarized space-wave field radiated in the perpendicular bisector plane of the antenna; and 2, a vertically polarized groundwave field radia ted along the axis of t he antenna. This vertically polarized field is zero at right angles to the an tenna. These fi elds have been experimentally verified. The use of a 50-kilocycle horizontal half-"'ave antenna for vertical-incidence ionospheric sounding experime nts is described. The radiation pat tern of this a ntenn a is ,,-ell s uited for ionospheric soundings sin ce a receiver located in t he g roundwave null receives only t h e r eflected s kywave s ign al. Grou nd-res istivitv measu remen ts mad e at a number oflocations in Central a nd Southern California were con·dated with t he geology of t he te rrain . Th is correlation showed t hat the g round resistivity is highest (a cond ition n ecessary for optimum a nte nna e ffi ciency) in areas where the und erlyin g rock formation s are r elat ively unfractured . The amount of annual ra infall a nd other climatic cond itions h ave li ttle or no effe ct on t he res istivity. Fina lly, a unique a ntenna sys te m is prese nted wh ich employs r esonan t loading circuits to convert a section of a n ex ist in g power line into a ho ri zon ta l h alf-wave very-lo,,--freq ucncy transmitt in g antenna.