Topband: Skywaves from Monopole Surface Waves

[Michael Tope]

I have long had a suspicion that some fraction of the power in surface 
wave must be "converted" to skywave as the surface wave encounters 
discontinuities in the ground medium (both physical geometry and 
dielectric parameters). Some folks I know from work were doing research 
on low-loss dielectric waveguides for microwave and millimeter waves 
(somewhat analogous to an optical fiber for RF). The degree to which 
these dielectric waveguides won't radiate despite not having a 
conductive outer shield is a function of how smooth the bends are and 
the degree to which discontinuities are minimized.

Another way to look at this is to ask the question - how would a 
vertical perform if it were installed on a perfectly uniform ground of 
average conductivity that conformed to the ideal geoid as compared with 
a more realistic installation - hills, mountains, lakes, and other 
abrupt changes in characteristics of the surface wave medium? In the 
former case, would the surface wave contribute less or more to the 
skywave power at low angles than in the latter case?

73, Mike W4EF......................

On 10/3/2012 9:05 AM, Richard Fry wrote:
> The elevation patterns of vertical monopoles over real earth has been 
> discussed in recent threads here 
> (http://lists.contesting.com/archives//html/Topband/2012-10/msg00140.html). 
> The common belief based on NEC far-field elevation patterns for those 
> conditions shows little relative field at low vertical angles, and 
> zero field in the horizontal plane.  However the surface wave must be 
> included in a complete analysis of monopole performance, because it 
> contributes substantial low-angle radiation that will reach the 
> ionosphere to generate skywave service under the right conditions.
>
> Below on this topic is part of an e-mail exchange of a few months ago 
> between Gerald Burke of Lawrence-Livermore National Laboratory and me, 
> and is quoted with his written permission.  As many will recognize, 
> Mr. Burke is co-author of the software engines used in NEC computer 
> programs.
>
> This text applies to NEC surface wave plots attached to my e-mail to him.
>
>>> Hello Mr. Burke -
>
>>> Would you expect the fields at elevation angles of 1 to 10 degrees
>>> in these plots to continue on to the ionosphere, and under the right
>>> conditions be reflected back to the earth as skywaves?
>
>>> R. Fry
>
>> The low angle 1/R fields should reach the ionosphere, although 
>> perhaps not
>> accurately predicted by NEC, since it does not include the effects of 
>> earth
>> curvature and the ionosphere.
>>
>> Regards,
>> Jerry Burke
>> LLNL 
>
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