Coaxially fed dipole antenna

An antenna system which provides an improved RF balancing system for electrically short, coaxially fed antennas. Antenna system (10) includes a first longitudinally extending dipole assembly (11) which has a capacitive inductive voltage induced therein. A second longitudinally extended dipole assembly (13) is axially aligned with the first longitudinally extended dipole assembly (11) and is positionally displaced from the first dipole assembly (11). A mechanism for electrically coupling the first dipole assembly (11) to the second dipole assembly (13) is provided. The capacitive inductive voltage is substantially equalized between the first dipole assembly (11) and the second dipole assembly (13) for voltage balancing the first and second dipole assemblies (11 and 13), each with respect to the other.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention pertains to antenna systems. In particular, this invention 
relates to electrically short and coaxially fed antenna systems. More in 
particular, this invention pertains to an RF balancing system for 
electrically short and coaxially fed antenna systems. 
2. Prior Art 
Coaxially fed antenna systems having a half-wave dipole consisting of two 
pieces of one-quarter wave tubing which are axially aligned and center fed 
with coaxial cable is known in the prior art. Additionally, coaxial cable 
extending through one of the two tubular members is also known in the 
prior art, such prior art antennas utilizing techniques known in the art 
as Bazooka balun, which is a quarter wavelength piece of tubing passed 
over the coaxial cable. Such resonates and generally traps out any 
radiation over the coaxial cable. However, such prior art antenna systems 
are generally approximately one-half wavelength in overall extended 
direction. Such prior art antennas are exceedingly lengthy and do not 
allow for the utility of a shorter extended length antenna system, as is 
provided in the inventive concept. 
Other prior art antenna systems known to applicant include U.S. Pat. Nos. 
3,961,332; 3,735,413; 3,789,416; 3,611,397; 3,932,873; 2,344,171; 
2,234,234; and, 2,821,709. 
In some prior art systems such as that shown in U.S. Pat. No. 3,789,416, 
the feed line is introduced at right angles to the radiating element axes. 
This is in contradistinction to the subject invention concept, wherein the 
RF balancing is provided for coaxially fed antenna systems. Additionally, 
in prior U.S. Pat. No. 3,611,397, such systems incorporate feed lines at 
right angles to the antenna axis, which is substantially removed from the 
coaxial design of the subject invention concept antenna system. In many 
prior art systems such as that provided in U.S. Pat. No. 3,932,873, there 
is no RF compensation and further, such provides for antenna dimensions of 
a quarter-wavelength or greater which would be in contradistinction to the 
overall concept of the subject antenna system. 
SUMMARY OF THE INVENTION 
An antenna system which includes a first longitudinally extended dipole 
assembly having a capacitive inductive voltage induced therein. The 
antenna system further includes a second longitudinally extended dipole 
assembly which is substantially axially aligned with and positionally 
displaced from the first dipole assembly. A mechanism for electrically 
coupling the first dipole assembly to the second dipole assembly is 
provided wherein the capacitive inductive voltage is substantially 
equalized between the first dipole assembly and the second dipole assembly 
for voltage balancing the first and second dipole assemblies, each with 
respect to the other.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIGS. 1-9, there is shown antenna system 10 defining a 
short center-fed dipole system, extending in longitudinal direction 6. 
Antenna system 10, as herein described, has been successfully operated 
between 1.5-54.0 MHz and has been particularly successfully used within 
the CB bandwidth range of 26.965 MHz-27.405 MHz, and the amateur 
bandwidths of 14.000 MHz to 14.350 MHz, 21.000 MHz to 21.450 MHz, and 
28.000 to 29.700 MHz. Generally, within the CB bandwidth, half-wave 
antennas would necessitate extended lengths of approximately 17.5 feet, 
which would provide a half-wave antenna resonant in the CB band. In 
opposition, the subject antenna system 10 has an extended length in 
longitudinal direction 6 approximately 4 feet with an overall external 
diameter of approximately 1.0 inches. The entire system components of 
anntenna system 10 is mounted within plastic housing 8 and is then adapted 
as will be seen in following paragraphs to hang on a wall of a dwelling, 
from a picture hook, or from a drapery rod or some other like mounting 
mechanism. 
One of the key utilities is to provide antenna system 10 having an extended 
length in longitudinal direction 6 of less than one-half the wavelength 
associated with antenna systems resonant in the CB or amateur radio band. 
System 10 includes first dipole assembly 11 and second dipole assembly 13, 
as is shown in FIG. 9. The extension length of each of first dipole 
assemblies 11 and second dipole assembly 13 approximates 2 feet in length 
thus, each is less than one-quarter wavelength. If the combined dipole 
assemblies 11 and 13 were a full half-wavelength in their combined 
extended direction 6, the half of dipole assembly 11 or 13 through which a 
coaxial cable feed was admitted, would be a quarter-wavelength. This is a 
standard commercially well-known design commonly known as a quarter-wave 
Bazooka section that would decouple the coax from the RF fields. However, 
in such prior designs, half of the extended length of such antennas would 
approximate a quarter-wavelength, whereas in antenna system 10, as will be 
shown in following paragraphs, a half-length of the overall extended 
direction of antenna system 10 is less than a quarter-wavelength. In the 
common nomenclature of the antenna field of art, antenna system 10 would 
be referred to as an electrically short (less than one-half wavelength) 
center-fed dipole system. The overall advantages of antenna system 10 
allows the extended dimension in longitudinal direction 6 to be 
considerably smaller than previously known antenna systems of this general 
type and the particular decoupling scheme as will be provided allows for 
frequency independence. 
Referring now to FIGS. 1 and 9, antenna system 10 includes first 
longitudinally extended dipole assembly 11 having a capacitive inductive 
voltage induced therein. Additionally, system 10 further comprises second 
longitudinally extended dipole assembly 13 substantially axially aligned 
with and positionally displaced from first dipole assembly 11. Both first 
dipole assembly 11 and second dipole assembly 13 are encased within 
plastic housing 8 and is shown in FIGS. 1 and 2. 
First and second dipole assemblies 11 and 13 include extended and axially 
aligned respective aluminum tubes 12 and 14 separated by an insulator. 
Electrically conducting tubes 12 and 14 are electrically coupled each to 
the other through first and second loading coils 16 and 18. Second loading 
coil 18 is a generally small loading coil which is variable through 
shorted ring 20 extending around the external surface of plastic housing 
8, as is shown in FIG. 1. Ring 20 is formed of a short piece of aluminum 
tubing, which is continuous in the circumferential direction. 
Link coil 22 injects electrical power into primary or first loading coil 16 
in order to excite antenna system 10. Link coil 22 is electrically coupled 
to coaxial cable 24 which is a standard coaxial cable element, and 
electrical power is injected through first end cap 26 and coaxial fitting 
32, as is shown in FIGS. 1 and 2. Coaxial fitting 32 and first end cap 26 
are coupled to a standard coaxial connector assembly (not shown). End cap 
26 is a standard metallic cap made of copper and is used to mount the 
standard coaxial connector fitting 32. 
It is important to note that antenna system 10 is coaxially fed, wherein 
coaxial cable 24 extends through a center passage of tubing element 12, 
resulting in a coaxially center-fed short dipole antenna system 10. In 
previous systems, a large RF imbalance would exist due to the coaxial 
cable coming through one of the tubing members. An important consideration 
in providing for RF balance in system 10 was to insert electrical 
conductor element 28 within tube 14 of second dipole assembly 13, as is 
clearly shown in the schematic diagram of FIG. 9. Conductor element 28 has 
the overall characteristic that its external diameter is substantially 
equal to the external diameter of coaxial cable 24 inserted in 
longitudinal direction 6 within aluminum tube 12. In this manner, an equal 
amount of capacitive inductive voltage pick-up is provided on conductor 
element 28, as is provided from one-half of dipole antenna system 10 on 
first dipole assembly 11, as is generated in coaxial cable 24. In this 
manner, antenna system 10 is RF balanced. This coupling system in 
combination with link coil 22, first and second loading coils 16 and 18, 
provides for a mechanism for electrically coupling first dipole assembly 
11 to second dipole assembly 13, in a manner such that the capacitive 
inductive voltage is substantially equalized between first dipole assembly 
11 and second dipole assembly 13 for voltage balancing first and second 
dipole assemblies 11 and 13, each with respect to the other. 
Electrical conducting element 28 is generally independent of the material 
being used, but must have substantially the same external diameter as 
coaxial cable 24. As a matter of practicality and convenience, antenna 
system 10 of the subject inventive concept, provides for conductor element 
28 being coaxial cable similar to coaxial cable 24, as previously 
described. Conductor element 28 is not coupled to other elements, but is 
merely insertable within aluminum tube 14. Conductor element 28 only 
includes a connection to one end of the braid of coaxial cable 24 through 
jumper link 30, as shown in FIG. 9. 
Thus, as has previously been described, first dipole assembly 11 includes 
first tubular dipole element 12 having an extension length less than a 
quarter-wavelength. Additionally, assembly 11 includes first center 
conductor element 24 which may be a coaxial cable extending through first 
tubular dipole element 12 and conductor element 24 has an electrical feed 
point on a first end thereof, and is coupled to the electrical coupling 
mechanism on a second end thereof, as is clearly seen in FIG. 9. Further, 
second dipole assembly 13 is provided with second tubular dipole element 
14 having an extension length also less than a quarter-wavelength, similar 
to that for first tubular dipole element 12. Second center conductor 
element 28 extends through second tubular dipole element 14, and second 
center conductor element 28 is electrically decoupled from second tubular 
dipole element 14 and first tubular dipole element 12, as has been 
described in previous paragraphs. 
Referring now to FIG. 2, there is shown the cutaway sections of antenna 
system 10 providing for all of the assembly elements contained therein. 
First end cap 26 is coupled in the standard manner to coaxial connector or 
fitting 32, that the operator would attach coaxial cable from his/her 
transmitter/receiver. Coaxial fitting 32 is mechanically fastened to first 
end cap 26 through a threaded insert not important to the inventive 
concept of the subject invention. End cap 26 is mounted to plastic housing 
8 through mounting screw 34, as is shown. Coaxial cable end 25 through 
which power is injected into antenna system 10, is prepared in a manner 
such that the braid portion and center conductor couples to coaxial 
connector assembly through coaxial fitting 32 in a standard well-known 
manner. Coaxial cable 24 includes the normal or standard outer plastic 
covering or housing, with a center conductor and coaxial cable braid. 
Coaxial cable 24 extends in longitudinal direction 6 through plastic shim 
tubing 36, which interfaces with an internal circumferential surface of 
plastic housing 8 and provides a through opening within which coaxial 
cable 24 may be inserted. Plastic shim tubing 36 is utilized to hold the 
various elements contained within housing 8 in fixed constrainment to 
prevent relative displacement of elements contained therein. 
Coaxial cable 24 extends through plastic tubing 38 which is contiguously 
mounted in aligned manner with plastic shim tubing 36, as is shown. 
Additionally, plastic tubing 38 is force fit into first dipole tubular 
element 12. Plastic tubing 38 is provided to maintain coaxial cable 24 in 
an axially centered position within conductor 12 and to electrically 
insulate coaxial cable 24 from aluminum tubing 12, as is clearly seen. 
Coaxial cable 24 may not be positioned near or substantially in the 
neighborhood of conductor 12 due to the fact that there may be 
burn-through or arc-over problems with the resulting possibility of a 
flash being initiated through the insulation of coaxial cable 24 into the 
coax proper, which would undoubtedly have the effect of the voltage 
antenna system 10 rising to an unacceptable high degree under transmit 
conditions. 
Plastic tubing 38 extends in axial or longitudinal direction 6 through only 
a portion of the axial extension of tubing 12. Plastic tubing 38 
terminates in end section 39, as is shown. A plurality of plastic disks 40 
having a through opening are mounted over coaxial cable 24, as is shown. 
Each of plastic disks interface with an internal surface of aluminum 
tubing 12 and are displaced each from the other in axial direction 6. 
Plastic disks 40 are secured to cable 24 prior to assembly within plastic 
housing 8 and aluminum tubing 12. Thus, coaxial cable 24 is insulated from 
aluminum tubing 12 both by plastic disks 40 and by air throughout the 
extension of coaxial cable 24 within aluminum tubing 12. 
The central portion of antenna system 10 is constructed on base or center 
plastic tubing 42. Coaxial cable 24 passing from coaxial connector 32 is 
inserted within center plastic tubing 42 and terminates short of link coil 
22. As is shown in FIGS. 2 and 3, the central portion of coaxial cable 24 
is coupled to link coil 22 at the coupling point 44. As is seen, link coil 
22 is helically wound around an external surface of center plastic tubing 
42 and is coupled to the central portion of coaxial cable 24 through an 
opening formed in a sidewall of tubing 42. The braid of coaxial cable 24 
is coupled to an opposing end of link coil 22 at coupling point 46, as is 
shown in FIGS. 2 and 4. Link coil 22 is the mechanism by which power is 
injected into antenna system 10, and such is wound coaxially in radial 
alignment with first loading coil 16 helically wound external to plastic 
housing 8, as is seen in FIGS. 2 and 1. Center braid 48 extends external 
to plastic tubing 42 and extends in axial direction 6 passing through the 
opening in tubing 42 provided for coupling point 46. Metal braid 48 may be 
the braid used for conductor element 28 and as has been previously 
described, such does not have to be formed of coaxial braid, however, such 
has been used for commercial economic reasons. 
Center metal braid 48 passes through opening 50 internal to center plastic 
tubing 42 and longitudinally extends under second loading coil 18 within 
tubing 42. Second loading coil 18, being the adjustment coil for adjusting 
the center resonant frequency of antenna system 10. Second loading coil 18 
is variably adjustable by sliding shorted ring 20 in longitudinal 
direction 6 and such shorted ring 20 is slidably mounted on an exterior 
surface of plastic housing 8, as is clearly shown. Such is user or 
operator adjustable to vary the inductance of second loading coil 18. As 
shown in FIGS. 2 and 6, center metal braid 48 passes internal to center 
plastic tubing 42 through opening 50 formed in a lateral sidewall of 
tubing 42. The metal braid exits tubing 42 through opening 54 passing 
external to tubing 42 and being defined as external section 52, shown in 
FIG. 2. External section 52 then passes internal to tubing 42 through 
opening 56 and joins the main body of coaxial cable 28. 
In operation during manufacture, a portion of the insulation of coaxial 
cable 28 is skinned or removed and the standard center conductor is pulled 
free. The remaining braid is pulled out and snaked through the openings, 
as previously described. The interweaving or snaking of the braid of 
coaxial cable 28 is important in that such braid must not come too close 
to various other conductors of antenna system 10, or an RF flash problem 
may arise. Such flash problem may result in minor fires which may cause 
antenna system 10 to actually burn up and become useless. 
External section 52 passing through opening 56 to the center of antenna 
system 10 becomes the braid of the main body of balancing coaxial cable or 
conductor 28. Metallic clip 58 which may be an aluminum clip is formed in 
a one-piece manner of tubing with an opening extending in longitudinal 
direction 6. The opening provides a passageway for center metal braid 48 
to pass therethrough. Clip 58 is provided such that screw 60 can protrude 
through plastic housing 8 for mounting of first loading coil 16, as is 
shown. Additionally, screw member 62 is similarly provided to couple first 
loading coil 16, as is shown in FIG. 2. Note that screw member 62 passes 
through plastic housing 8 and contiguously contacts aluminum tube 12. 
Second screw member 60 contacts aluminum clip 58 in a contiguous manner. 
Aluminum clip 58 provides contact between outer coil or first loading coil 
16 and inner adjustment coil or second loading coil 18. As has been 
stated, both first loading coil 16 and second loading coil 18 are coupled 
to aluminum clip 58 through the screw mechanism system including screw 
members 60 and 74 shown in FIG. 5. 
Referring to shorted ring member 20, such is formed of a solid aluminum 
ring providing a sliding fit over plastic housing 8. When ring 20 is moved 
or displaced on plastic housing 8 in a manner such that it does not 
overlap second loading coil 18, such is a small loading coil having a 
predetermined inductance. As shorted ring 20 is displaced in a manner to 
overlap second loading coil 18, such comes into a range where it 
constitutes a shorted single turn length that is electrically coupled to 
second loading coil 18. This causes a decrease in the inductance of second 
loading coil 18 and such inductance may be varied dependent upon the 
degree of overlapping relation. Displacement of shorted ring 20 allows 
antenna system 10 to be user adjustable. Thus, the purpose of shorted ring 
20 is to allow second loading coil 18 to become an adjustable coil in 
order that the operator or user may set the center frequency wherever he 
or she desires over some predetermined range. The bandwidth of antenna 
system 10, as described herein, at 14 MHz is generally a usable bandwidth 
of plus or minus 50 kilohertz without displacement of shorted ring 20. By 
displacement of shorted ring 20, there has been found that the usable 
bandwidth has been increased to cover about 700 kilohertz. 
Referring now to second dipole assembly 13, there is shown conductor 28 
extending in axial direction 6 within aluminum tube 14. Conductor 28 
extends within plastic plug 64 which interfaces on an exterior surface 
with aluminum tube 14 and on an interior surface with conductor 28. Plug 
64 insulates conductor 28 and such is adhesively bonded or otherwise 
fixedly attached to plastic plug 64 in order that conductor 28 is 
non-movable. 
Antenna system 10 second dipole assembly 13 terminates in tube cap member 
66 which is a vinyl tube covering adhesively bonded over plastic housing 8 
in order to seal out any moisture, dirt or other undesirable particulate 
matter. Second cap or over cap member 70 formed of a plastic-like 
composition is force fit over tube cap 66 which has as its purpose to hold 
or fixedly constrain an electrically non-conductive block 68, which may be 
a wood plug to serve as an anchor point when a brass cup hook member 72 is 
inserted therein. Cup hook 72 merely increases the utility of antenna 
system 10 by allowing such system 10 to be hooked to an external 
appendage, such as a drapery rod or other like fixture. 
Although this invention has been described in connection with specific 
forms and embodiments thereof, it will be appreciated that various 
modifications other than those discussed above may be resorted to without 
departing from the spirit or scope of the invention. For example, 
equivalent elements may be substituted for those specifically shown and 
described, certain features may be used independently of other features, 
and in certain cases, particular locations of elements may be reversed or 
interposed, all without departing from the spirit or the scope of the 
invention as defined in the appended claims.