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Monopole Radiation Patterns

 
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R. Fry
Antenna Theory Regular


Joined: 06 Jun 2011
Posts: 43
Location: Illinois USA

PostPosted: Mon Jun 06, 2011 10:37 am    Post subject: Monopole Radiation Patterns Reply with quote

The text and graphic at http://www.antenna-theory.com/antennas/monopole.php apply to the radiation pattern at an infinite distance from a monopole over a finite ground plane, showing that maximum radiated field is skewed away from the horizontal plane, with essentially zero radiation in the horizontal plane.

However this is untrue for the fields existing closer to the monopole, as is demonstrated by the performance of AM broadcast stations -- which use the very strong surface (ground) wave radiated by monopoles of all heights to at least 5/8-wavelength to provide daytime coverage to distances of 200 miles and more, in some cases.

The link below leads to data from the experiments of Brown, Lewis & Epstein showing that the groundwave fields measured 3/10 of a mile from a monopole of heights ranging from 50 to 100 degrees using 113 x 0.412-wave buried radials was within a few percent of the theoretical maximum for a perfect monopole using a perfect ground plane. These tests were made at a site in New Jersey where earth conductivity is no better than 4 mS/m. The test frequency was 3 MHz.

http://i62.photobucket.com/albums/h85/rfry-100/BLandERadials.gif
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