Coil loaded antenna embedded in glass fibre

A freestanding glass fibre antenna having at least two antenna sections, a lower section having a mounting base and a coupling at the upper end, and having linear radiating members of conductive material, and an upper section having a cooperating coupling at the lower end, and incorporating a single radiating element formed of conductive material, arranged in a helically wound coil fashion having a plurality of turns, and embedded permanently in the glass fibre material of such antenna, the coil wound radiating element being arranged to tune the antenna to the desired frequency range.

The invention relates to a free-standing antenna formed of reinforced glass 
fibre material, and in particular to such an antenna incorporating a 
single helically wound radiating coil of conductive material therein. 
BACKGROUND OF THE INVENTION 
One form of free-standing glass fibre antenna is shown in U.S. Pat. No. 
3,725,944. 
The antenna disclosed there is formed of multiple layers of glass fibres 
laid up in a certain manner, and incorporates a plurality of radiating 
members extending in a generally longitudinal linear fashion up the 
antenna. 
Antennas made in accordance with such patent, were found to be greatly 
superior to other free-standing antennas which had hitherto been 
available, and were able to withstand stresses due to weather, wind and 
the like, to a greater extent than any previous antennas then available. 
Such antennas are particularly useful in military applications, in 
particular in mobile military applications such as at sea, or in 
situations where a powerful long-distance antenna must be set up and in 
operation at very short notice. 
When they are subject to repeated bending stresses, for example due to high 
winds, or due to violent movement of the base upon which they are mounted, 
i.e., a ship in a rough seal, substantial stresses are imposed in the 
radiating conductors. Accordingly, a plurality of such conductors, all of 
them being generally linear members are employed. In this way, even 
through some such conductors would gradually break down, under repeated 
flexing of the antenna, the antenna would continue to function. 
However, the use of a plurality of radiating members, of a generally linear 
nature, arranged spaced apart radially around the structure of the antenna 
imposes certain limitations on the effectiveness of the antenna for 
radiating radio transmissions. 
It is of course well known that an antenna must be tuned to the resonant 
frequency of the transmission. This may be done by varying the length of 
the antenna, in simple cases. However, in the present invention, the 
length of the antenna is determined initially in the design stage and once 
erected, it cannot be changed. Tuning of the antenna is therefore usually 
effected by the use of a coil, connected at the base of the antenna. In 
the present case, where very high powered transmissions are involved, this 
introduces further problems and limitations, and also adversely affects 
the radiation characteristics of the antenna itself. 
BRIEF SUMMARY OF THE INVENTION 
The invention therefore seeks to overcome the disadvantages described 
above, by the provision of a free-standing glass fibre antenna, comprising 
at least two antenna sections, a lower one of such sections having a 
mounting base thereon at the lower end, and a coupling at the upper end, 
and having a plurality of linear radiating members of conductive material, 
and an upper one of such sections having a cooperating coupling at the 
lower end, and an upper one of such sections incorporating a single 
radiating element formed of conductive material, arranged in helically 
wound coil fashion having a plurality of turns, and embedded permanently 
in the glass fibre material of such antenna, said coil wound radiating 
element thereby tuning said antenna to the desired frequency range. 
More specifically, the invention provides such an antenna incorporating 
male and female couplings and conductive junction means in such male and 
female couplings, and wherein said radiating members and said radiating 
element are in electrical connection therewith, whereby to constitute a 
continuous single electrical radiating structure, comprised of such coil 
wound element and said linear members. 
The invention further provides such an antenna wherein the electrical 
connection between said radiating member and said conductive coupling, 
comprises a plurality of relatively short and separate conductive 
connecting members, all being connected to said coil wound radiating 
element, and extending therefrom, and being located at spaced intervals 
around said antenna, and connected to said conductive coupling at spaced 
intervals therearound. 
More particularly, it is the object of the invention that, where three or 
more antenna sections are employed, the coil-wound radiating element shall 
be located in the second such section, counting from the base, i.e., the 
section next adjacent to the base section. 
It will of course be understood that the helically wound radiating element 
is engineered in such a manner as to maximize the transmitting efficiency 
of the antenna over a predetermined wave band of desired transmission. 
The various features of novelty which characterize the invention are 
pointed out with particularity in the claims annexed to and forming a part 
of this disclosure. For a better understanding of the invention, its 
operating advantages and specific objects attained by its use, reference 
should be had to the accompanying drawings and descriptive matter in which 
there are illustrated and described preferred embodiments of the invention 
.

DESCRIPTION OF A SPECIFIC EMBODIMENT 
As shown in the drawings, the present embodiment of the invention comprises 
an antenna formed in three sections, namely a bottom section or part 10, 
an intermediate section or part 12 and a top section or part 14. 
It will of course be appreciated that the antenna can equally well be made 
with a two-part construction, or could have a four-part or five-part 
construction, or even more for certain purposes. 
The bottom section 10 comprises a generally cylindrical hollow body portion 
20, formed of reinforced glass fibre material, and a generally flared base 
22, having a fastening flange 24 therearound also formed integrally of 
such glass fibre material. 
The structure may be formed of multiple layers of glass fibre material, 
with the strands or rovings extending in different directions, as 
disclosed in the aforesaid U.S. Patent referred to above. 
At its upper end, the bottom section 10 is provided with a male coupling 
sleeve 26, having exterior threads 28 formed therearound. 
Coupling 26 is positioned on the upper end of the main body 20, the main 
body 20 being formed with an integral reduced diameter neck portion 30, 
adapted to fit tightly within the coupling 26. 
A plurality of fastening pins 32 extend through suitable openings in the 
male coupling sleeve 26, and are bonded into the neck portion 30, so as to 
secure the coupling sleeve 26 in position. 
In the majority of cases the coupling sleeve 26 will, of course, 
additionally be bonded in place by adhesive e.g. an epoxy adhesive to the 
glass fibre material of the neck 30. 
Bottom section 10 incorporates a plurality of more or less linear 
conductive radiating elements 34 embedded in glass fibre material of main 
body 20. The conductive elements 34 are connected by a ring-like connector 
36, at their lower end, and ring 36 is provided with an electrical 
coupling device 30, by means of which it may be coupled to a transmitter 
unit (not shown). 
The upper ends of elements 34 are connected to the male coupling sleeve 26, 
being located radially spaced apart around the upper end of the main body 
20, and extending through neck 30 into electrical connection with the 
interior of the male sleeve 26. 
Male sleeve 26 is itself, of course, made of metal, and is therefore an 
electrically conducting member. 
Preferably, the elements 34 will all be fastened, for example, by soldering 
to the interior of the male sleeve 26 which extends beyond the end of the 
neck 30. 
The central section 12 of the antenna is also of similar glass fibre 
construction, having a main body portion 20a, and having at its upper end, 
a reduced neck 30a, and a male coupling sleeve 26a provided with threads. 
In this section of the antenna, the use of linear conductive elements 34 is 
dispensed with and instead a single conductive radiating element 34a is 
employed. Element 34a is embedded in the glass fibre material of the main 
body 20a, and is wound in a continuous helical manner so as to form a 
single winding continuous coil-like structure with a plurality of turns 
along the length of main body 20a. The individual turns of element 34a are 
spaced apart from one another and are secured in such spacing by the 
surrounding glass fibre material. 
The electrical conductor 34a is provided with two additional upper terminal 
connecting members 38a and 40a, which are equally spaced apart with the 
upper end of conductor 34a radially around the reduced neck 30a, and 
extend therethrough, together with the end of the conductor 34a itself, 
into electrical contact with the interior of the sleeve 26a and are 
soldered thereto. 
At the lower end of the main body portion 20a, an enlarged interior bore 42 
is provided in the glass fibre material, in which is fitted a female 
coupling sleeve 44, having interior threads 46 therein. 
The exterior of the sleeve 44 is provided with a series of axially spaced 
apart annular ridges or grooves 48, for the purpose of making a firmer and 
more secure engagement with the reinforced glass fibre material 
surrounding the enlarged bore 42, in which the sleeve 44 is received. 
At its lower end, the conductor 34a is itself terminally connected to the 
exterior female sleeve 44, and two additional end connectors 50 and 52 are 
embedded in the body 20a attached to the conductor 34a, and are also 
connected to sleeve 44, in radially spaced apart location therearound, on 
its exterior, preferably with solder. Sleeve 44 being formed of metal is 
therefore electrically conductive, and it will thus be seen that a 
continuous electrical connection exists between the radiating elements 34 
in the bottom section 10, via the upper male sleeve 26, through the female 
sleeve 44, to the single radiating element 34a in the centre section 12, 
and then to the male sleeve 26a at the upper end of the centre section. 
It will also be noted that the male sleeve 26a is similarly fastened by 
means of pins, and adhesive (not shown) to the neck 30a. 
The upper or top portion 14 of the antenna 10 is also provided with a main 
body 20b, and having at its lower end, an enlarged bore 42a, into which is 
received a female sleeve 44a, having interior threads and exterior annular 
grooves in the same manner as sleeve 44. This section of the antenna uses 
a plurality of generally linear conductive radiating elements 34b, in the 
same way as bottom section 10. 
The lower end of conductive members 34b are terminally connected to the 
sleeve 44a. Sleeve 44a being of metal and therefore electrically 
conductive, therefore provides a continuous connection between male sleeve 
26a and the conductive members 34b. 
Conductive members 34b extend upwardly along the length of the upper main 
body portion 20b, and are fastened at the top end thereof, to a suitable 
metallic convex typically hemispherical member, shown generally as 54. 
Fastening bolts 56 extend through suitable threaded bores in the ends of 
the main body portions 20 and 20a and through sleeves 44 and 26 to lock 
the sections together. 
Visual markings or indicia 58 on the exterior provide an easy means of 
ensuring that the couplings are correctly fastened, sufficiently tightly 
to ensure proper interconnection but not so overly tight as to cause 
possible damage to the structure. 
In the past, for example when using with antennas such as those illustrated 
in U.S. Pat. No. 3,725,944, it was possible to construct freestanding 
antennas which were tuned to operate at fairly low frequencies, in the 
range of between 2 and 30 megahertz. However, it was generally speaking 
impractical to attempt to construct such an antenna which would be tuned 
to operate at frequencies much below this range. 
In accordance with the invention however it is now possible to construct a 
whip antenna which is tuned to radiate very low frequencies, in the range 
from about 300 kilohertz, up to 2 megahertz, and at high power, in the 
range of 10 kilowatts, with great efficiency. The whip antenna of the 
invention, by the use of the intermediate section incorporatins a 
coil-wound radiating element, is effectively tuned to the resonant 
frequency range most suitable for low frequencies, for which it is used. 
Coil loading of the antenna at its base would not be as effective, since in 
this location the coil would generate a high voltage at the feed point 
when the whip is operated at low frequency. Most antenna couplers cannot 
handle the high feed point voltage developed at low frequencies. 
In accordance with the invention, the inductive loading is located in the 
middle of the antenna and reasonably far away from the feed point. In this 
way, the feed point voltage is maintained within acceptable limits, and in 
addition, the radiation characteristics along the length of the antenna 
are optimized so as to produce the most favourable profile. 
As mentioned above, such antennas may be made in four or five sections. In 
the case where the antenna is more than three sections, then it is 
desirable that the coil wound radiating element 34a shall be contained in 
the second section of the antenna, i.e., the section next adjacent to the 
base or bottom section. 
The foregoing is a description of a preferred embodiment of the invention 
which is given here by way of example only. The invention is not to be 
taken as limited to any of the specific features as described, but 
comprehends all such variations thereof as come within the scope of the 
appended claims.