Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to a novel form of a wide -
bandwidth antenna. 1-
Various antenna systems are commonly employed to ;
provide wide bandwidth spectra, the majority of which rely upon
a plurality of physically separate, electrieally interconnected
antennae, arranged to individually cover specific narrow regions
of the band. Thus, each antenna is tuned to a specific region,
and the total combination i5 able to cover the sum of these
regions extending over the required band of frequencies.
Multiple antennae arrangements of this type sufer
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from the disadvantages of expense, bulk, and complexity, and it
would clearly be advantageous to provide a single, light-weight
antenna capable of e~ficiently covering a wide ranye of
~requencies.
One type of single wide bandwidth antenna was described
by R. J. Wohlers ~20th USAF Antenna Symposium, 1967) in a paper
entitled "The GWIA, An Extremely Wide Bandwidth Low-Dispersior
Antenna". However, like other single wide bandwidth antennae
which have been-proposed,~ the Wohlers design suffers from
relatively high cost, complexity and bulk.
An object of the present invention is to provide a
single light-weight antenna, which i9 relatively inexpensive
and simple in construction, yet highly efficient over a wide
. ..
range of frequencies. ;
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Thus, according~to the present invention, there is 1-
provided a~wide bandwidth~antenna comprisLng~an active antenna
;element of generally conical~surface configurat~on, said element
having~discrete areas thereo~f respectL;vely modified to be
frequency-responsive about individua~l ones-of algeometrically
~30~ progres~ive~series of~f~requency maxima.withln said bandwidth, ~ ;
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the dimensions of said areas being progressively scaled by a
substantially constant factor corresponding to the multiplication
factor of said series.
The invention will no~l be described by way of example
only and with reference to the accompanying drawings, wherein~
Figure 1 is a cross-sectional view of an antenna
according to one embodiment of the invention; and
. Figure 2 is a cross-sectional view of an antenna .
according to yet a further embodiment of.the invention.
Considering, firstly, Figure 1, the arrangement
illustrated is based upon the electromagnetic modelling or
scaling log-periodic concept, which generally provides that if
all the dimensions of a lossless. antenna are changed by a
~actor ~, then the antenna performance is identical at a 1.
fre~uency 1/p. Thus, in Figure 1, there 1s shown a bi-conical
antenna having coaxially allgned elements lO and 11 respectively.
The elements are embedded Ln cylindrical foam block 12, which is
contained within a tubul~ar membersl3.The apices of the elements
: 10 and 11 are;co-ad~acent and spaced by.a smaLl amount, and
~-:20 antenna.feed..wires.14 and 15 are respectively connected thereto~
The.. arrangement thus far described is well.known in the field of ~.
.. bi-conical antenna structures.
The surfaces of the~conical elements lO;and 11 are
.stepped,~ as~at lOa, lOb,:lOc,;...etc.~and lla, llb,~ llc,~ ...etc., ~ l
respectively. ~As will~be~ appreciated~from a;consideration of ~ - .
the~drawing,~:the respectivel:surface~po~tions of t.he elements~
~ 10 ànd 1l between successive~steps are o:f-frusto-conical ~
:~ configuration and each~such portlon will be responsive to~a ~ ~ ¦
eaific~:narrow bandwidth.~ofsfrequenciea. It will~-further be
30~ ~seen that~.the surface portions bet~een successive steps are . ; :
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formed with a constant angle.of taper, and thus, the mean radii .. ;.:
of the portions vary by a constant factor. Since the surface
area and dimensions of each portion are directly proportional
to the mean radius thereof, the antenna structure may be
considered to be a series of antennae whose dimensions are
changed by a constant factor ~, Therefore, the performance of . .
each of these individually considered"antennae"is identical at -
a frequency of l/p times the frequency of the adjacent "antenna".
Referring specifically,:again, to Figure 1, if the
.lO antenna portion between the innermost step lOf and the apex of .
the element lO is responsive to a frequency F, then having
regard to the foregoing, the antenna portions between successive ~ .
steps lOf and lOe; lOe and lOd ... lOb and lOa will have
identical performances at frequencies Fj~p, Fjp2 ,,,.,F/p6,
respectively. ~earing in mind that the foreg~ing are centre
fre~uencies about which the respective conicaI surface "antennae"
,
have optimum perormance,~.it occurs.in.practice that there
... . ,:
is sufficient overlap between the effective frequency response :~
. maxima and mlnima of adjacent suxfaces to provide a substantially
20- flat.overall response~.or the complete antenna of from F to F/p6. . ~ .
. Figure 2 shows an alternative embod.5i.ment of the
invention~.using slots instead of steps to prov.ide the necessary
.. re~uency scaling. The antenna Lllustrated in Figure 2 again
comprises conical elements 20~and ~1 embedded with~a generally
cylindrical foam.rubber block 22.. ~r~he.block 22 ls:contained ~ :
within~a tubular membar 23~and antenna~feed~wires 24 and 25 are `. :
pro~ided~.for the elements.:20 and 2L,:respectively. ~Slots~26 are -.
.arranged.circularly.around the surfaces.of.the~elements~20 and
. 21, the slot~dimensions~being scaled~in accordance-:with~the , . :
~3~ respectLve radLi of the~cLrcular slot arrays, the soale faotor
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again being p. Thus, if -there are seven slot arrays - as in
the specific embodiment of Figure 2 - then, by analogy with
the discussion set forth above, the frequency response of the
antenna will be substantially flat from F to F/p7.
It will be appreciated that the slots or steps need
not be circularly arrayed around the conical surface. For
example, a spiral array may effectively be employed, if desired,
or indeed any other type of array which will give the required
constant-ratio gradation of the effective antenna elements.
Furthermore, the invention is not restricted to bi-
conical antennae of th~ type specifically described. The
invention is equally applicable to other types o conical-
,
element antennae - for example, cross bi-conicals which utilize ;
two bi-conical arrays mutually oriented at 90. The invention
is also applicable to discone antennae, which comprises a
conical element in~conjunction wlth~a di~sc-shaped element pro~
vided at the apex of the conical element and located coaxial
therewith. ~ ~
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With respect to the materials employed, it may be - ;
noted that the cylindrical ~oam block shown in each of Figures
1 and 2 is ~or mechanical support only and has no influence
upon the electrical properties of the antenna. It will be
; appreciated that any~sultable~electrlcally ~insulating mate~rial
may~b~e utillzed for thls~purpose and that a similar electrlc~
ally~insu~lation reinforcément;materlal~may be~placed inside~
the~conical~ elements,~if desirèd.
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