Method and apparatus for making a molded cellular antenna coil

An antenna for a wireless communicating device can be set at a precise frequency, in the as formed state. A coil antenna is precisely held in a mold, while an appropriate plastic is molded therearound, with no distortion of the coil, to fix a precise shape for the coil. The recovered, plastic-encased coil requires little or no follow-up treatment before it can be used in a wireless communication device as an antenna.

This invention relates to a cellular antenna coil; and, more particularly, 
to a molded cellular antenna coil encapsulated in a resin material for 
holding the antenna coil in the proper position at a specific dimension 
for maximum effectiveness for use in a wireless communication device, and 
a method and an apparatus for making the same. 
BACKGROUND OF THE INVENTION 
Currently, contemporary mass produced wireless communication devices, such 
as: a cellular telephone, a pager, or a similar device, are dependent on 
the use of sophisticated, specially tuned antennas to perform the function 
of sending and receiving the radio-wave signals, that they require to 
function. The recent introduction of digital technology on a widespread 
and growing basis continues to place further performance demands on 
antennas. In order for a wireless communication device to operate at 
maximum efficiency, the signal quality must be maintained. 
In an antenna for a cellular telephone, it is especially critical to 
provide an extremely specific dimension for the antenna to achieve the 
maximum effectiveness for the cellular telephone as to range and clarity 
of signal. With this specific dimension maintained, the maximum 
effectiveness of the antenna, and hence the telephone or other 
communication device, is achieved. 
For any wireless communication device, the antenna must be tuned to a 
specific radio frequency and be capable of rejection of all other unwanted 
radio frequencies to prevent reception from fading. Any antenna for such a 
device must be engineered to send and receive signals within a very 
specific radio frequency range. The effectiveness (and even the basic 
ability to function) of a wireless communication device is intimately 
linked to the consistent performance of the antenna assembly. 
In the United States, these operating frequencies are mandated and assigned 
by the Federal Communication Commission. In other countries, they are 
likewise assigned by the appropriate governmental regulatory agencies in 
specific countries. In order for the antenna to perform within the strict 
frequency parameters mandated by the United States and foreign 
governments, the antenna assembly must be manufactured to extremely 
exacting, difficult to reproduce, tolerances and specifications. 
One of the key components of the antenna assembly, and a component which is 
critical to the antenna's ability to operate within the specified radio 
frequency range, is the antenna's coil assembly. Due to the difficulty of 
maintaining such exacting tolerances in a high production environment, 
most antennas produced today require some type of auxiliary adjustment 
method, which enables them to be individually tuned to the government 
mandated operating frequency. 
Because it enables the antenna manufacturer to incorporate desirable 
features (such as mounting holes, assembly positioning features, 
structural integrity, and attachments points for other required 
components), the plastic injection molding process is often used to 
manufacture the coil assembly of an antenna. 
Frequently, the antenna's primary component (a conductive coil typically 
constructed from metal), is encapsulated in a body of plastic. The process 
of encapsulating components in plastic is commonly referred to as insert 
molding. The dimension of the coil must be accurate within 0.1 millimeter 
(0.004 inch) for the tang and the coil. 
To produce a coil assembly using the insert molding process, the following 
procedures are typically employed. 
(1) The conductive coil constructed from metal wire (typically formed in 
the configuration of a common coil spring and typically manufactured on 
traditional spring forming machinery) is placed on a type of mandrel 
called a core pin. 
(2) The core pin, with the coil in place, is placed into the cavity of an 
injection mold. The cavity is the section of the mold which has been 
formed into the configuration of the finished molded part. The mold is 
then closed. 
(3) Molten plastic is injected under very high pressure into the mold 
cavity, (over and around the coil on the core pin) at a high rate of 
speed. 
(4) The molten plastic is allowed to cool, the mold is opened, and the coil 
(now encapsulated in plastic) is removed from the core pin. The coil is 
now ready to be used in a cellular telephone or other wireless 
communication device. 
In the manufacturing process described above, the high injection pressures, 
and high molten plastic injection speeds inherent in the injection molding 
process can cause undesirable movement and can change the desired 
dimensions of the conductive coil on the core pin. This undesirable 
movement, coupled with the basic inability of the coil spring manufacturer 
to adequately control the winding process used to manufacture the 
conductive coil, results in finished products with imprecisely located 
conductive coils. 
The precise dimensional relationships of the coil assembly are critical 
factors, which govern the radio frequency range and performance of the 
characteristics of the complete antenna assembly. Some of these factors 
are: 
(1) overall wire length of the conductive coil; 
(2) overall winding length of the conductive coil; 
(3) conductive coil location within the plastic encapsulation; 
(4) overall conductive coil diameter; and 
(5) coil to coil pitch. 
Because such precise dimensional control is usually unattainable in the as 
molded state with commonly used manufacturing practices, it is often 
necessary to compensate for any manufacturing discrepancies. Most often, 
overcoming these manufacturing inconsistencies (including, but not limited 
to, imprecise coil production and undesirable coil movement during 
molding) is a costly process which requires that each individual coil 
assembly be "tuned" to the proper operating frequency before the finished 
coil assembly can be used in production. 
Therefore, it is very desirable that a method of producing coil assemblies 
which are useable to manufacturers of wireless communication devices in 
the as molded state be developed. To do so will eliminate the costly and 
time consuming requirement of individually tuning the antenna of each 
finished wireless communication device. 
To produce such a pre-trued or accurately tuned antenna coil assembly 
requires: 
(1) exceptionally tight "as molded" tolerances; and 
(2) greatly reduced dimensional variability of the conductive coil 
location, within the surrounding molded plastic, around a specified 
standard in its "as molded" state. 
Based upon the radio frequency response requirements of each individual 
application, various dimensions of the conductive coil portion of the 
assembly can be altered. The conductive coil variables can include, but 
are not limited to, wire diameter, overall length, outside coil diameter, 
inside coil diameter, the "pitch angle" of the coil winding, and the space 
between the individual coils. 
Since there is no such thing as a "standard" coil assembly showing, for the 
sake of clarity, a single representative version for the purpose of 
explaining the invention may be used. In this manner greatly improved 
dimensional control of the most critical aspects of the conductive coil, 
that is overall length and coil to coil pitch specifications. 
Otherwise difficult to mold resins or plastics are operable herein. The 
particular mold design is applicable to an engineering grade plastic or 
resin, or to a high temperature plastic resin. The mold of this invention 
is designed to be filled with a resin at a lower pressure and a lower 
temperature than is customary in the art. 
SUMMARY OF THE INVENTION 
Among the many objectives of this invention is the provision of a pre-tuned 
antenna for a wireless communication device. 
Another objective of this invention is to provide an apparatus to form a 
pre-tuned antenna for a wireless communication device. 
Yet another objective of this invention is to provide a method of forming a 
pre-tuned antenna for a wireless communication device. 
Still another objective of this invention is to provide an apparatus to 
form a pretuned antenna, which avoids the use of an inner core. 
Additionally, an objective of this invention is to provide a method to form 
a pretuned antenna, which avoids the use of an inner core. 
Also, an objective of this invention is to provide an antenna for a 
wireless communication device having a specific dimension. 
A further objective of this invention is to provide an antenna for a 
wireless communication device having a desired function. 
A still further objective of this invention is to provide an antenna for a 
wireless communication device having good signal quality. 
Yet a further objective of this invention is to provide an antenna for a 
wireless communication device tuned to a desired frequency. 
Another objective of this invention is to provide an antenna for a wireless 
communication device, which rejects unwanted radio frequencies. 
Yet another objective of this invention is to provide an antenna for a 
wireless communication device, which avoids fading reception. 
Still another objective of this invention is to provide an antenna for a 
wireless communication device, which has consistent performance. 
Additionally, an objective of this invention is to provide an antenna for a 
wireless communication device, which has extremely exacting tolerances and 
specifications. 
Also, an objective of this invention is to provide an antenna for a 
wireless communication device, which has difficult to reproduce tolerances 
and specifications. 
A further objective of this invention is to provide an antenna for a 
wireless communication device to operate within a specified radio 
frequency range. 
A still further objective of this invention is to provide an antenna for a 
wireless communication device having a good coil assembly. 
Yet a further objective of this invention is to provide an antenna for a 
wireless communication device, which avoids an auxiliary adjustment. 
These and other objectives of the invention (which other objectives become 
clear by consideration of the specification, claims and drawings as a 
whole) are met by providing an antenna for a wireless communicating device 
set at a precise frequency, in the as formed state. To accomplish these 
desired results, a coil antenna is precisely held in a mold, while an 
appropriate plastic is molded therearound, with no distortion of the coil, 
to fix a precise shape for the coil. The recovered, plastic-encased coil 
requires little or no follow-up treatment before it can be used in a 
wireless communication device as an antenna.

Throughout the figures of the drawings where the same part appears in more 
than one figure the same number is applied thereto. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An antenna coil is formed by holding the coil in the mold in the precise 
position. A handle supports at least one coil in the precisely desired 
position. The handle is then inserted into the mold. The coil on the 
handle is further supported by the mold. An appropriate resin or plastic 
substance is then injected into the mold around each coil. The resin is 
cooled. The resulting antenna is then recovered. 
Pressure pads within the mold contact the outside of the coil, and combine 
with a top holding device and a bottom holding device to hold the coil on 
the handle in a precisely desired position. A resin is then injected into 
the mold in order to seal that coil in the precisely desired position, due 
to its precisely positive, substantially immovable location during 
molding. 
In other words, each coil used in the antenna must have a predetermined 
shape and size. Each coil must be held at the predetermined shape and size 
while the plastic substance is applied thereto, and then cooled. In this 
fashion, the precise position of the coil is set, and the precise 
structure of the antenna is predetermined. The molding method then permits 
recovery of an antenna with little or no after molding treatment. 
Thus, the 0.1 millimeter (0.004 inch) is maintained at the top end stop, 
and the tang end or bottom end of the antenna coil. The tang end is 
positively positioned on the handle with a bottom stop. With this holding, 
the desired results are achieved and the coil is specifically positioned. 
The process and apparatus herein disclosed do not rely on, or need, or use 
an integral, inner core member to achieve the dimensional accuracy or 
frequency desired for the end product. The reliance and associated expense 
of a multi-step inner core member process is virtually eliminated. 
The pressure pads hold the coil while the plastic is applied or injected 
into the mold. The fact that the pressure pads may leave part of the coil 
exposed through the plastic is not a problem, as long as the coil is held 
in the proper position. Pressure pads also serve to hold the desired 
diameter of the coil. The gate of the coil and the pressure relief 
provides for relief from any pressure caused by the injection of the resin 
and misshaping of the coil. 
The invention further detailed below describes a novel construction method, 
part design, tooling process and manufacturing technique for producing a 
high precision, insert molded, coil assembly for use as an antenna in a 
wireless communication device. A typical wireless communication device 
includes, but is not limited to, a cellular telephone, a pager, and 
similar devices. 
The basis of the invention is to permit the coil assembly manufacturer to 
produce an insert-molded, high precision coil assembly, which is able to 
be used in its "as molded" state, and requires no costly and time 
consuming calibration or pre-tuning prior to, or after, its installation 
on the communication device assembly line. 
The configuration of the specific coil assembly shown below is meant to be 
representative, but not limited to, the type of high precision coil 
assembly which may be manufactured by incorporating the features of the 
invention. This coil assembly is designed to be used as an antenna in 
wireless communication devices with little or no treatment after molding. 
It especially desirable to use the antenna in the as molded state. 
With the positioning of the coil and the positive location thereof, the 
pitch to pitch stability of each loop in the coil is achieved. Also with 
the positioning of the coil at the top and the bottom thereof, a preset 
position for pretuning of the antenna is achieved. The pressure pad holds 
the coil within the resin area. There is a release of the pad which 
permits efficient encapsulation of the coil. 
For cellular telephones, it is highly desirable to manufacture the antennas 
in large quantities, while maintaining consistent and predictable 
electrical results. The consistency leaves little error and little 
flexibility. The range between the top and the bottom end of the coil must 
be within 0.1 millimeter (0.004 inch). 
The key reason for having the antenna tuned properly is so that the 
distributive capacitance of the coil can be relied on to form the desired 
resonance circuit. Also, it is important that no variable reception means 
for the antenna be permitted. Injection molding techniques can achieve the 
desired results. 
However, it is critical that the coil be properly positioned within the 
mold and held until the proper plastic or resin is injected at the proper 
time with the proper temperature in the proper position. The use of 
helical antennas is well known for communication devices. Specifically, 
these communication devices operate in the very high frequency range (VHF) 
and lower portion of the ultra high frequency range (UHF). These antennas 
may be physically shorter than the standard antenna. 
A helical antenna is constructed by winding the helical coil and then 
encasing the coil in a plastic sleeve. After encapsulation, the coil must 
customarily be trimmed. This trimming is now avoided with great savings of 
time, labor and expense. Close tolerances from this encapsulation for the 
coil in order to achieve the desired resonance of the encapsulated coil 
and the resulting antenna require little or no trimming when compared to 
prior processes. 
Trimming is required to adjust the frequency resonance of antennas formed 
by the prior art. This adjustment is required because the various 
parameters, such as the pitch of the helical coil, can be changed during 
construction. Therefore, it is not possible to precut the antenna to the 
desired resonance frequencies prior to molding the plastic therearound. 
The coil and hence the antenna must maintain close dimensional tolerances. 
This is required so that the inductiveness of the antenna can achieve the 
desired result for the desired frequency. The dimensional tolerances are 
equally important with the required inductiveness. 
Referring now to FIG. 1, FIG. 2, FIG. 3, and FIG. 4, the antenna 100 of 
this invention is depicted. The antenna includes a coil 110. Coil 110 is 
encapsulated in a resinous or plastic substance 132. The plastic substance 
132 is any suitable, injection-moldable, shapeable material having the 
appropriate electronic properties for coating coil 110 to form antenna 
100. A typical plastic substance 132 may be selected from engineering 
grade plastic or resins described in U.S. Pat. No. 5,336,075 to Stephen A. 
Motisi. Plastic substance 132 is usually a thermoplastic resin. 
Coil 110 includes a central circular coil portion 136; bottom end, or tang 
end 138; and a top end 140. Tang end 138 includes a rod 144. Rod 144 
extends from central coil 136 and is parallel to the central axis of 
central coil 136. 
A first groove 122 appears in plastic substance 132 exposing coil 110 
substantially tangential to coil 110 and parallel to the central axis 
thereof and is formed by a top mold pad 202 (FIG. 11). Two other grooves 
are present and mutually spaced at 120 degree angles from first groove 122 
and each other. 
The second groove 124 being due to a first mold pinch bar 244 and the third 
groove 126 being due to a second mold pinch bar 246. Adjacent to second 
groove 124 is a molding ridge 128. 
Base platform 130 is customarily tangential to the tang end 138 of the 
antenna 100. The top end 140 is oppositely disposed from the base platform 
130. The antenna 100 is basically a hollow cylinder with the plastic 
substance 132 molded around a central coil 136. More particularly, the 
bottom or tang end 138 and the top end 140 are specifically shown in FIG. 
4. 
The central coil 136 includes a series of loops 142. The shape and spacing 
of loops 142 are critical and must be held in proper position within 0.1 
of a millimeter. This is accomplished by the structure of mold 200. 
In FIG. 5, the as molded antenna 100 are seen. A shaped plastic mass may be 
removed from the mold 200 (FIG. 8). This shaped mass is plastic molded 
mass described as molded assembly 102, shown in this embodiment with four 
of antenna 100 thereon. It includes plastic substance 132 hardened around 
coil 110, while coil 110 is held in particular dimensions. 
Residue 150 thereof is separated from each antenna 100 in order to recover 
the antenna 100, by simply breaking a plurality of thin straps 152, formed 
in the shaping process by mold 200. Straps 152 are situated between 
residue 150 and antenna 100. The antenna 100 may then be used in a 
communication device, with little or no subsequent treatment. 
With FIG. 6 showing handle assembly 120, it can be seen how as molded 
assembly 102 is formed. Handle assembly 120 includes a gripping support 
162, a coil receiving support 184, a sliding bar 186 and a pair of bar 
supports 174. 
Gripping support 162 permits handle assembly 120 to be held and inserted 
into mold 200 after coils 110 are placed thereon. Gripping support 162 is 
secured to coil receiving support 184 at a central portion thereof in a 
substantially perpendicular relationship. 
The bar supports 174 are mounted at each end of coil receiving support 184 
also in a substantially perpendicular relationship. However bar supports 
174 are on a side of coil receiving support 184 oppositely disposed from 
gripping support 162. 
Bar supports 174 receive the sliding bar 186. Sliding bar 186 slides around 
coil pipe 180 to contact bottom end, or tang end 138 of coil 110. This 
contact combines with twist stop 172 to hold each end of coil 110. Below 
described top mold pad 202 and bottom pinch bars 244 and 246 complete the 
hold on coil 110 at the appropriate spot, while the plastic substance 132 
is applied. 
While FIG. 6 depicts four of coil receiving member 166 on coil receiving 
support 184, each capable of receiving a coil 110, this number can, of 
course, be adjusted. This number and the corresponding structure therefor 
increases or decreases depending on the appropriateness of the 
manufacturing process. 
Adding FIG. 7 to the consideration, each coil 110 is mounted on a coil 
receiving member 166 of coil receiving support 184. Each coil receiving 
member 166 has a top end receiving device 168 which holds the top end 140 
in proper position. 
A first groove 122 is formed by the top mold pinch bar called top mold pad 
202 for the purposes herein. Two other grooves are present at 120 degree 
angles therefrom, the second groove being 124 and the third groove being 
126. Adjacent to second groove 124 is a molding ridge 128. Base platform 
130 is tangential to the tang end 138 of the antenna. The top end 140 is 
oppositely disposed from the tang end 138. 
Gripping support 162 provides a means for gripping the handle assembly 120 
and inserting the same in the mold 200. The coil receiving support 184 
also includes an enlarged base 170. Enlarged base 170 has a larger 
diameter than the interior diameter of the coil 110. The enlarged base 170 
extends from the gripping support 162 of handle assembly 120 and has a 
twist stop 172 adjacent to the enlarged base 170 and protruding upwardly 
therefrom. 
The top end 140 of the coil 110 contacts the twist stop 172 and holds the 
coil 110 at the top end 140. The twist stop 172 is merely an extension of 
enlarged base 170. 
The handle assembly 120 includes a gripping support 162 so that the handle 
assembly 120 may be held at one end thereof and a sliding bar 174 at the 
other end thereof. Therebetween is the coil receiving support 184. The 
coil receiving support 184 has mounted thereon the coil receiving member 
166, which includes the enlarged base 170 and coil pipe 180. The enlarged 
base has a diameter of sufficient size to stop the coil 110 at the top end 
140 thereof at an appropriate point. The coil pipe 180 has a diameter of 
sufficient size to receive the coil 110. 
There is a mechanism of a twist stop 172 on each coil receiving support 
184, which stops the top end 140 of the coil 110 at a particular point on 
the coil pipe 180 adjacent to the enlarged base 180. Coil pipe 180 
combines with enlarged base 170, so that it extends above coil receiving 
support 184, with a diameter smaller than the diameter of enlarged base 
170. Coil pipe 180 thus receives coil 110 at the central coil 136. 
FIG. 8 brings the mold 200 into the consideration. In the embodiment shown, 
four (4) of coil receiving member 166 are depicted on handle assembly 120 
and are inserted into the mold 200 with handle assembly 120. FIG. 9 and 
FIG. 10 combine to clarify the structure of mold 200. 
The mold 200 includes a top member 220 and bottom member 240. Within the 
bottom member 240, is a handle receiver 262. The handle receiver 262 (FIG. 
9) positions the handle assembly 120 properly and permits the coils 110 to 
rest thereon during the molding process. The gripping support 162 and the 
mold 200 structure are specifically designed to hold the handle assembly 
120 in the appropriate position, within mold 200. 
As a further support for positioning of top member 220 and bottom member 
240, are corner guides. Corner guides include diagonally opposed corner 
posts 354 on top member 220, corresponding corner apertures 356 on bottom 
member 240. 
The mold 200 includes the appropriate locking members 350 and the handle 
apertures 352 to support the handle assembly 120 in the desired place. 
Upper locking posts 256 on top member 220 and lower locking posts 254 on 
bottom member 240 within the mold 200 hold the handle assembly 120 at the 
precise location desired. Guide holes 250 in the bottom member 240 of the 
mold 200 receive large guide posts 252. 
Upper small locking posts 256 are shown as four in number to be received by 
small guide apertures 258. Small guide apertures 258 are located in bottom 
member 240. 
Guide posts 252 in the top member 220 of the mold 200 assure proper 
alignment of the mold. In this fashion, not only can the proper amount of 
plastic substance 132 be injected into the proper position, the desired 
structure and positioning of the coil 110 can be achieved. 
FIG. 11 and FIG. 12 explain the grooves in antenna 100 and the holding of 
the handle assembly 120. The mold 200 also includes a top mold pad 202 and 
bottom pinch bars 244 and 246 to contact the coils 110 at the appropriate 
spot. The top member 220 also combines top mold pad 202 with the bottom 
pinch bars 244 and 246 to form at substantially 120.degree. degree angles 
from each other. 
The first groove 122 is formed by top mold pad 202. The second groove 124 
is due to the first mold pinch bar 244, and the third groove 126 is due to 
a second mold pinch bar 246. Adjacent to second groove 124 is a molding 
ridge 128 formed by ridge cavity 248 in bottom member 240. 
The top member 220 has therein the first shaping part 222 of the mold 200. 
The bottom member 240 has therein second shaping part 242 of the mold 200. 
The first shaping part 222 and the second shaping part 242 cooperate to 
form the as molded assembly 102. 
The top member 220 of the mold 200 and the bottom member 240 of the mold 
200 are brought together in any typical fashion such as by hydraulic 
members. This is accomplished along mold supports 300 preferably four in 
number in each corner of the top member 220 of the mold 200 and the bottom 
member 240 of the mold 200. 
As can be seen in FIG. 13 and FIG. 14, after the mold 200 is closed, it is 
feasible to inject plastic substance 132 therein. The plastic substance 
132 must be sufficiently strong and non-interfering with transmission to 
permit the antenna 100 to be held and formed. Between the handle assembly 
120 and the pinch bars 202, 244 and 246, the coil 110 is held in precisely 
the right position until the plastic substance 132 is applied thereto and 
cooled. In this fashion, the antenna 100 may be recovered from the as 
molded assembly 102 of FIG. 5 and the resulting antennas 100 separated 
therefrom. 
As the top member 220 and the bottom member 240 come together, oppositely 
disposed from the handle end 302, is an injection port 304 best indicated 
in FIG. 15, but shown in FIG. 9 and FIG. 10. Through this injection port 
304, the appropriate plastic substance 132 is inserted. Appropriate tubes 
306 guide the plastic substance 132 around the antenna 100 at the points 
desired. 
FIG. 16 makes clear the holding of the coil 110. Due to the presence of the 
handle assembly 120 and the pinch bars 202, 244, and 246, the coils 110 do 
not move as the plastic substance 132 applied thereto. The plastic 
substance 132 is adjusted for appropriate viscosity and molding 
capability, and electronic transmission and reception, the adjustment 
being well within the scope of a person having ordinary skill in the art 
to do so. 
This application--taken as a whole with the specification, claims, 
abstract, and drawings--provides sufficient information for a person 
having ordinary skill in the art to practice the invention disclosed and 
claimed herein. Any measures necessary to practice this invention are well 
within the skill of a person having ordinary skill in this art after that 
person has made a careful study of this disclosure. 
Because of this disclosure and solely because of this disclosure, 
modification of this method and apparatus can become clear to a person 
having ordinary skill in this particular art. Such modifications are 
clearly covered by this disclosure.