Measurements of low-angle radiation from a monopole

Abstract

Experimental m easuremen ts usi ng scale model techniqu es ha ve been carried o u t to determine t he effectiveness of a ground system of lon g-wire radials to obtain low a ng les of dep ar ture of t ra nsmission . Since transmission was to be in one direction only, t he gro und wires were laid out to form a g round-plane sector approximately 18° wide cen te red i n t he direction of trans mi ssion. The antenna was a base-driven vertical monopole. Measurem en ts were made of t he relative respon se in decibels for t he mo nopole used as a receivin g anten na at a freq uency of 400 m egacycles per seco nd . The target tr a nsmi tter a nte nna was always lo wted at a di stance of 200 wave lengths. At t his separation the ground pla ne sector was in t he neal' fi eld of t he target t ransmitting an tenna a nd appropriate co rrections must be m ade.The received signa l strength improvement due to the presence of t he g round secto r was approximately 14 decibels. The m eas ured lobe positions of the first a nd seco nd beam m aximum s and t he fir st null a rc in good ag ree men t with t heo ry.

Pattern of a Linear Antenna Erected Over a Tapered Ground Screen

“…On a number of occasions it has been suggested that low-angle radiation froill ground-based h.f. antennas can be enhanced by the use of large ground planes (Wait 1956(Wait , 1963Wilson 1961;Andersen 1963). T o be effective, these must reduce significantly the surface impedance of the foreground out to distances froill the antenna comparable with or greater than a Fresnel zone.…”

Reception of skywave signals near a coastline

“…One method of obtaining an improvement in the reception at low angles is to use an extended ground-wire system in the direction of propagation (or reception) (A.C. Wilson;1961) . Another method would be to chuose the antenna site near a coastline in order to utilize the high conductivity of sea-water wherever it is possible.…”