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.
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. PA1 (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. PA1 (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. PA1 (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. PA1 (1) overall wire length of the conductive coil; PA1 (2) overall winding length of the conductive coil; PA1 (3) conductive coil location within the plastic encapsulation; PA1 (4) overall conductive coil diameter; and PA1 (5) coil to coil pitch. PA1 (1) exceptionally tight "as molded" tolerances; and PA1 (2) greatly reduced dimensional variability of the conductive coil location, within the surrounding molded plastic, around a specified standard in its "as molded" state.
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:
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:
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.