Dual-Z0 Stubs
Cecil Moore wrote:
"One cannot blame one`s ignorance on a lack of textbooks."
True. The most reliable in my opinion is Terman`s 1955 opus "Electronic
and Radio Engineering".
Terman agrees with Cecil.
On page 854 Terman writes:
"The laws governing such radiation are obtained by using Maxwell`s
equations to express the fields associated with the wire; when this is
done there is found to be a component, termed the radiation field,
having a strength that varies inversely with distance."
Terman then gives the formula for the electric field strength in terms
of distance from the elementary doublets in the wire that make up the
antennna to a distant observing point P, and angle of the direction of
point P with respect to a plane perpendicular to the axis of the
elementary doublet. The strength of the radiated field is distributed in
space in accordance with the doughnut pattern for a thin wire which is
short compared with wavelength and has a figure-of-8 cross section.
Illustrations are provided on page 865. On page 866 Terman illustrates
current distribution on an antenna open circuited at both ends and made
up of elementary doublets. On page 867 Terman says:
"A wire antenna is a circuit with distributed constants; hence the
current distribution in a wire antenna that results from the application
of a localized voltage follows the principles discussed in Chap. 4
(Transmission Lines), and depends upon the antenna length, measured in
wavelengths; the terminations at the ends of the antenna wire; and the
losses in the system. The current distribution is also affected by the
ratio of the wire length to diameter in situations where the wire is
unusually thick. Under most circumstances the losses are sufficiently
low and the ratio of wire length to diameter sufficiently great so that
to a first approximation very closely the current distribution can be
taken as that for a line with zero losses; it then has the
characteristics discussed in 4-5.
Best regards, Richard Harrison. KB5WZI
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