Radio Propagation Over Plane Earth— Field Strength Curves 



By CHARLES R. BURROWS 



Curves are presented to facilitate the calculation of radio propa- 

 gation over plane earth. The magnitude and phase of the reflection 

 coefificient for all conductivities of interest and for four values of 

 the dielectric constant are presented in the form of curves from 

 which the significant quantities may be read with the same degree 

 of accuracy for all conditions. Simple equations, from which the 

 effect of raising the antennas above the earth's surface may be 

 readily calculated, are presented. 



Introduction 

 npHIS paper is intended to facilitate the calculation of radio propa- 

 -^ gation over plane earth. In Part I curves are presented that 

 show the decrease of field strength with distance for antennas on the 

 surface of the earth. In these curves the results obtained by Sommer- 

 feld ^ and Rolf ^ are corrected and certain approximations ' introduced 

 by Rolf to reduce the number of variables to a workable number are 

 eliminated. For a discussion of the Sommerfeld-Rolf curves, the 

 reader is referred to a companion paper.* 



Part II is concerned with the more general case of antennas above 

 the surface of the earth. The complete equation that gives the field 

 strength for antennas at any height above the earth is reduced to a 

 simple equation which allows the calculation of the field under con- 

 ditions of practical interest. 



To facilitate field strength calculations, the values of the reflection 

 coefilicient are presented in the form of curves from which the significant 

 quantities may be read with the required degree of accuracy for ail 

 angles of incidence. 



Preliminary Remarks 

 A rectilinear antenna in free space generates an electric field whose 

 effective value in the equatorial plane of the antenna at a distance 

 large compared with the wave-length and the antenna length is 



where HI is equal to the line integral of the current taken over the 

 ^ Numbers refer to bibliography at end. 



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