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A VIRTUAL GROUND BALUN FOR THE
SUPPRESSION OF ANYONE OF THE TWO BRANCHES OF AN ½ A WAVELENGTH OPEN DIPOLE
ANTENNA
by Francesco Errante
Scientific purposes :
a. The balun described hereby enables to demonstrate that the
½ wavelength open dipole antenna, also known as "Hertzian Dipole" is
not an "elementary antenna" (by definition an elementary antenna is an
aerial where the condition of resonance and radiation cannot take place without
the presence of all its parts) but it is, instead, an "elementary
array" of 2 radiating/captating elements of a physical length equal to ¼
of a wavelength each, which are electrically arranged in a counterphase, while
being fed in the middle of them;
b. The balun described hereby enables to demonstrate that once
a virtual ground node is available, it is possible to receive and transmit
radio-electric signals through the space by employing a single
radiating/captating element of a physical length equal to ¼ of a wavelength,
without the need for a natural nor an artificial ground plane;
(see --> ERRANTE's ANTENNA )
c. The balun described hereby enables to demonstrate that each
of the two branches of an ½ wavelength open dipole antenna, at its frequency of
resonance, exhibits an absolute impedance value of 35 Ohm, unbalanced and
referred to the virtual ground node;
d. The balun described hereby enables to demonstrate that each
of the two branches of an ½ wavelength open dipole antenna, exhibits a
phase-angle difference of +/- 90 degree with respect to the virtual ground
node.
Circuit
description
In the field of radio-engineering, a multitude of systems are well-known for
matching an ½ wavelength open dipole to an unbalanced transmission line, they
are usually referred to as balun (a compound term meaning
"balanced-unbalanced"). State of the art balun(s) do not allow feeding of the
two branches of an ½ wavelength open dipole independently from each other and
as a result of that, they do not allow to verify whether it possible to
suppress anyone of them without interfering with the condition of resonance and
irradiation of the remaining one. The invention described hereby allows
to feed each of the two branches of an ½ wavelength open dipole independently,
so that they can become electrically independent from each other allowing,
therefore, to suppress anyone of them without repercussions on the condition of
resonance and radiation of the remaining one.
(similarly, a device for splitting up the ½ a
wavelength folded dipole antenna is described here)
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This result has been achieved by means of a lumped-constants
radio-electric circuit, based around a broad-band radio-frequency electric
transformer(1) winded on a binocular type ferrite core having a primary
winding(2) exhibiting an impedance value equal the one of the transmission
line(3) being used and a center-tapped secondary winding(4) exhibiting an
impedance value of 35 + 35 Ohm. The said impedance values are referred to the
virtual ground. ("virtual ground" is defined as a point in an
electrical circuit that appears to be at ground, but is not actually attached
to ground, it is therefore, a node having a 0 degree phase angle difference
with respect to ground and has the same electrical potential as the Earth")
The virtual ground node has been obtained by providing the transformer's
secondary winding(4) with a center-tap(5), effectively splitting the secondary
winding in two sections. The virtual ground is then made available to the whole
of the network by a short electrical connection(6) to the device
chassis(7).
The transformer's working point is optimized by compensation with the
employment of high-voltage RF duty capacitors(8).
The suppression of one of the two branches of the open dipole is made by
manually operating the high insulation resistance switch(9) diverting the
radio-electric signal from the transformer(1) off the branch of the dipole(11
or 12) and into one lead of the non-inductive 35 Ohm dummy-load(10) while the
other lead of the dummy-load is attached to the virtual ground circuit.
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