The link below leads to a scholarly analysis of EH and CFA antenna configurations. Its principal author is Valentino Trainotti, a Senior Member of the IEEE.
Here are some salient points from the conclusions in that paper:
• Antenna operation for each f2-window has been compared to a reference monopole of the same height and on
the same ground plane and top-loading conditions.
• It can be concluded that the disk presence has always a
deleterious effect, decreasing the antenna performance.
• The CFA performance is always a little worst than the
reference monopole in gain and bandwidth. The antenna
performance increases as either the antenna height or top-
loading is increased, in the same way as for any standard
short monopole. Also, a simple monopole has a similar
or better performance with an easier tuning system.
• CFA antenna has the same radiation pattern and near
field distribution as any short monopole, then no Poynting
Vector Synthesis (PVS) can be seen close to the CFA
antenna.
• A CFA gain improvement is obtained installing it on
a building roof, in the same manner as for a standard
monopole
The gain improvement in mounting a CFA or EH on a building roof is produced by radiation from the outside of the shield of the longer coaxial cable connecting the transmitter to the antenna -- not because the elevated antenna components themselves produce higher gain at higher elevations above the earth.
http://materias.fi.uba.ar/6654/download/CFAantenna.pdf
This article is certainly deep water for hobbyists but the conclusions can be useful.
One question I have is what is meant by Poynting Vector Synthesis?
I am familiar with the Poynting vector but what is the synthesis part? The E cross H would seem to apply to any radiating field.
Nonetheless, it is my impression that the base coil loaded vertical monopole over radials is still the best a Part15er can do for AM.
Neil
I'm thinking that the term Poynting Vector Synthesis refers to the expectations of the developers and proponents of the CFA/EH antenna that it generates the E-field independently of the H-field, and which (they claim) permits an efficient antenna that is very small compared to the wavelengths it radiates.
Here is what Wikipedia says about this concept (bold attributes there were added by me):
... According to Maxwell's equations, a spatially varying electric field is always associated with a magnetic field that changes over time. Likewise, a spatially varying magnetic field is associated with specific changes over time in the electric field. In an electromagnetic wave, the changes in the electric field are always accompanied by a wave in the magnetic field in one direction, and vice versa. This relationship between the two occurs without either type field causing the other; rather, they occur together in the same way that time and space changes occur together and are interlinked in special relativity. ...
Yes, deep water indeed. But while the details in Trainotti's paper are difficult to follow, the conclusions they lead to should be useful to almost everyone with an interest in the subject (as you wrote).
Perhaps the term "vector systhesis" refers to modifying the E and H relative near field strengths to achieve a certain impedance however in the far field the impedance is 377 ohms. I don't see any advantage to doing this.
For some background see this link beginning at about 6:30 into the video.
The presentation is in reference to measuring E and H fields near circuit boards but the theory of what happens transitioning from near to far field is worth a look.
Neil
Nice video on probing E&H fields near circuit boards.
I found an explanation of the term Poynting Vector Synthesis as used by the principal developer of the CFA antenna -- Dr. F. M. Kabbary of the Egyptian Radio and TV Union in Cairo, Egypt.
It is given in paragraph two on page one of the paper linked below.
http://materias.fi.uba.ar/6654/download/CFATCheck.pdf