[0001] The present invention relates to communication antennas of the azimuthal omnidirectional
type, being more particularly directed to such antennas adapted for mast-mounting
and relatively broad banded to operate over a range of communication frequencies,
such as, for example, in the 30 to 88 megahertz range.
[0002] There are a myriad of various types of omnidirectional communications and related
antennas that have been successfully used in the art including, for example, those
described in U.S. Letters Patent Nos. 3,324,476; 3,534,378; 4,218,687; and 4,598,296
of common assignee herewith. These antennas have operated as monopoles and dipoles
with various types of matching networks and ground counterpoises and the like, heretofore
relatively independent of the mast-mounting or supporting structure upon which they
have been employed. It has now been discovered, however, that a very efficient type
of guy wire support for the mast and antenna can be formed into a simultaneously operative
effective radial antenna ground plane antenna, leading to relatively low cost and
highly efficient and improved support systems of this character.
[0003] It is accordingly an object of the present invention to provide a new and improved
mast-mounted omnidirectional communications antenna of the monopole type in which
supporting guy wires are also simultaneously used effectively as elevated ground plane
elements for the advantages above stated, and others.
[0004] Other and further objects will be explained hereinafter and are more particularly
delineated in the appended claims.
[0005] In summary, however, from one of its viewpoints, the invention embraces an azimuthal
omnidirectional communications mast-mounted antenna having, in combination, a monopole
antenna encased in a dielectric cylinder, a conductive base cylinder securable to
a mast and into which the dielectric cylinder is inserted and secured, a plurality
of conductive wires symmetrically disposed about and radially depending at an acute
angle from the outer surface of the base cylinder in the form of guy wires conically
distributed about the base cylinder and mast and connected at their free ends to guy
rope extensions for anchoring the antenna and mast, means for establishing electrical
connection of the inner ends of the guy wires to the base cylinder, and coaxial conductor
means, the inner conductor of which connects to the monopole antenna near the base
of the dielectric cylinder and the outer conductor of which connects to the base cylinder,
the length of the guy wires being adjusted to about one quarter of the wavelength
of the communication frequency(ies) so that the guy wires serve also simultaneously
as an elevated radial ground plane or counterpoise for the antenna. Preferred details
and best mode construction are hereinafter presented.
[0006] The invention will now be described in connection with the accompanying drawings,
Fig. 1 of which is a side elevation of the antenna and support system in preferred
form;
Fig. 2 is a top elevation with one type of combined guy wire-ground plane structure;
Fig. 3 is a view similar to Fig. 2 of a modification; and
Fig. 4 is a view similar to Fig. 1 of a further modification.
[0007] Referring to Fig. 1, an antenna A as of the monopole type, is shown encased within
a fiberglass or other dielectric cylindrical housing H, the lower end of which is
inserted within a conductive base cylinder or casting B, as of aluminum, for example,
to the inner walls of which the lower part of the housing H is secured as at S, such
as by glue.
[0008] As before stated, conducting metal guy wires G are provided symmetrically disposed
about and radially depending at an acute angle from the outer surface of the base
cylinder B in the form of a conically distributed arrangement that envelops about
the base cylinder B and the mast M, to which the same may be secured as by a latch
clamp L. The guy wires are shown having inner end loops 1 for structurally connecting
into apertures in conductive ears 3 at symmetrically spaced points about the conductive
base cylinder B, shown as at 90-degree positions in Fig. 2. In accordance with the
invention, however, the metallic radial guy wires G do not just serve as guy supports
for the antenna-base-mast structure, but also as electrical ground plane or counterpoise
elements which is made possible by electrically conductive connectors 5 making good
electrical connection between the metallic guys G and the conductive ears 3 of the
conductive base B, as more particularly shown in Fig. 1.
[0009] The length of the elements G for the electrical purposes they serve, as distinguished
from the structural guying purposes, are made approximately one quarter of the wavelength
of the communication frequency or frequencies to be used, as is the vertical length
of the antenna A. As more particularly shown in Fig. 1, the inner conductor of a coaxial
feed line connects with the antenna A at a bottom edge thereof as at I, and the outer
conductor connects with the ground base cylinder B.
[0010] In the system of Fig. 1, the antenna A may be a planar monopole sheet and it may
be curved into cylindrical C-shape form within the outer fiberglass housing A (and
about an inner fiberglass tube, if desired).
[0011] If, on the other hand, a linear type of monopole antenna is desired, as shown at
A′ in Fig. 4, the inner conductor of the coaxial line I will again connect with the
bottom end of the antenna A′ through a matching network N shown disposed within the
base cylinder B, again with the outer cylinder capacitively coupled to the antenna
and feedline and connected to the outer conductor O of the coaxial line.
[0012] In this manner, the metallic guy wires G serve not only for guying support of the
structure, but simultaneously as an elevated radial ground plane or surface or counterpoise
for the antenna, provided the remainder of the guying elements are non-conductive
guy ropes anchoring the structure to the ground or other surface as shown at R. The
free ends of the metallic guy elements G are therefore provided with further loops
1′ that loop with rope guys R that extend to the ground, permitting the guy wires
G to serve a guying function only for their length as a segment of the total guying
structure, and having appropriate electrical length, as before stated, simultaneously
to serve as an effective ground plane or surface for the antenna.
[0013] It has been found that a variation in the acute angle of the symmetrically disposed
guy segments G with respect to the vertical mast can play a desirable role in tilting
the elevational radiation pattern of the omnidirectional antenna. For example, with
an antenna constructed as shown in the embodiment of Fig. 1 and operating at 30 megahertz,
with an acute angle of the guy wire G of 30 degrees to the vertical mast, a symmetrical
doughnut shaped radiation pattern has been achieved, with the horizon being the symmetrical
axis thereof in the vertical plane. At 52 megahertz, the predetermined length of the
elements G caused a ten degree downward tilt in the elevational pattern; and at 88
megahertz, about a ten degree upward tilt. At a 45 degree acute angle of the elements
G, on the other hand, again at 30 megahertz, symmetry of the elevational pattern with
the horizon was attained. At 41 megahertz, however, a 15 degree upward tilt was observed,
as was the same achieved at 88 megahertz.
[0014] While the plurality of combined guy wire-ground plane elements G of Fig. 2 is illustrated
in the form of four radial spokes, further variations are possible and useful, including
the four-sided star of Fig. 3, which, though made of wire elements, in view of the
wavelengths involved, has been found to act as if they were solid sheets in terms
of broad-banding and affecting the radiation pattern and impedance matches of the
system.
[0015] Further modifications will occur to those skilled in this art, and such are considered
to fall within the spirit and scope of the invention as defined in the appended claims.
1. An azimuthal omnidirectional communications mast-mounted antenna having, in combination,
a monopole antenna encased in a dielectric cylinder; a conductive base cylinder securable
to a mast and into which the dielectric cylinder is inserted and secured; a plurality
of conductive wires symmetrically disposed about and radially depending at an acute
angle from the outer surface of the base cylinder in the form of guy wires conically
distributed about the base cylinder and mast and connected at their free ends to guy
rope extensions for anchoring the antenna and mast; means for establishing electrical
connection of the inner ends of the guy wires to the base cylinder; and coaxial conductor
means the inner conductor of which connects to the monopole antenna at the base of
the dielectric cylinder and the outer conductor of which connects to the base cylinder,
the length of the guy wires being adjusted to about a quarter of the wavelength of
the communication frequency(ies) so that the guy wires serve also simultaneously
as an elevated radial ground plane for the antenna.
2. An antenna as claimed in claim 1 and in which the plurality of guy wires comprises
four wires connected at 90° points about the base cylinder.
3. An antenna as claimed in claim 1 and in which the plurality of guy wires comprises
a four-sided star.
4. An antenna as claimed in claim 1 and in which the monopole antenna is substantially
a quarter-wavelength cylindrical sheet within the dielectric cylinder and to a bottom
edge of which the said inner conductor is connected.
5. An antenna as claimed in claim 1 and in which the antenna within the dielectric
cylinder is connected within the base cylinder through matching network means to
the inner conductor of the coaxial line.
6. An antenna as claimed in claim 1 and in which means is provided for varying the
angle of the guy wires to vary the tilt of the elevational radiation pattern of the
antenna for various frequencies.