2
$\begingroup$

This is a rather common belief among amateur radio operators, but is it true? A NEC analysis provides some insight on this concept.

$\endgroup$
2
$\begingroup$

Below is a NEC4.2 study comparing the fields radiated by an eighth-wave, series-fed vertical monopole driven against sets of thirty buried radials of 1/4 and 1/8 wavelength (other things equal).

The X axis shows field intensity (E), and the Y axis shows elevation (Z) above a flat Earth ground plane, at a horizontal distance of 100 meters from the base of the monopole.

The antenna system with 1/4-wave radial lengths generates a maximum field intensity 12.5% greater than the system with 1/8-wave radials.

The corresponding improvement in radiated power is 1.125² x 100% = 26.6% (approximately).

The increased radiation efficiency is the result of collecting more of the r-f currents flowing on and below the surface of the earth within a 1/2-wavelength radius from the base of the monopole, as a result of its radiation. The r-f resistance of the set of buried radials is a series circuit element whose I^2R loss reduces the r-f current that flows along the monopole, itself.

enter image description here

$\endgroup$
  • $\begingroup$ 1.125² ≈ 1.0 dB, no? $\endgroup$ – rclocher3 Sep 5 '19 at 21:08
  • $\begingroup$ Yes, approximately so (1.023... dB). $\endgroup$ – Richard Fry Sep 5 '19 at 21:38

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.