This invention relates to fractal antennas and, more particularly, to manufacturing fractal antennas using electroforming.
Antennas are used in a vast array of commercial applications that require radiation and/or reception of electromagnetic signals, such as cellular telephones, global positioning system (GPS) devices, and the like. Historically, Euclidean geometrical shapesxe2x80x94circles, squares, lines, triangles, etc.xe2x80x94have dominated antenna designs. A major drawback of such designs is that, as products incorporating antennas have become smaller and smaller, the effectiveness of antennas of these designs has decreased. This is because small sized antennas do not work well for several reasons due to the underlying electromagnetic principles.
In recent years, researchers have been applying fractal geometryxe2x80x94a non-Euclidean geometryxe2x80x94to antenna design. Fractal antennas have been developed and refined so that the traditional trade-off of lesser performance for smaller sized antennas has been minimized. Most of the benefit of fractal antennas has been seen in the performance of antenna arrays, single units that are actually arrays of up to thousands of small antennas. Use of fractal antennas in antenna arrays has allowed manufacturers to use only about a quarter of the number of elements in an array that were previously required.
However, it has been shown that even isolated antennas benefit from having a fractal shape. Bending a straight wire antenna into fractal shapes, for example, can pack the same antenna length into about a sixth of the area. At the same time, such a shape also generates electrical capacitance and inductance and provides a more sophisticated antenna.
Fractal antennas are twenty-five percent more efficient than the rubbery stub-like antennas found on most of today""s cellular telephones. In addition, they are cheaper to manufacture, operate on multiple bandsxe2x80x94thus allowing, for example, a GPS receiver to be build into the phonexe2x80x94and can be hidden away inside the body of the cell phone.
Currently, fractal antennas are manufactured using a traditional printed circuit board (PCB) process. Though there are several variations of PCB processes, generally, this process requires generating a film master of the antenna design, which is subsequently used to laminate dry-film etch resist to a copper/fiberglass substrate. The dry-film etch resist is exposed and then developed. The copper background is then etched with the antenna design. The etch resist is finally removed to provide the final product.
There are several problems that exist with utilizing such a method to produce fractal antennas. First, the etch resist must be photo patterned for every antenna produced. Second, the etching step requires hazardous material that must be disposed after the process is complete. Finally, copper foil on fiberglass substrate is relatively expensive.
Systems and methods are described herein that utilize an electroforming technique to manufacture fractal antennas. Electroforming is a technique that is used to produce metal parts that have accurate contours and dimensions. An electrically conductive mandrel is made the cathode of an electro-forming circuit that includes an electrolyte solution in which the electrically conductive cathode is immersed. The electrolyte solution contains dissolved salts of the metal to be deposited and the anode of the circuit is a suspended slab of the metal to be deposited, i.e., the metal that will form the antenna. A current flow is applied to the circuit and this causes the metal from the anode to build up on the antenna pattern on the mandrel cathode. An appropriate amount of metal is plated onto the mandrel to form an antenna of a desired thickness. The mandrel and the antenna are then separated from each other and the antenna is bonded to a low cost substrate to form the final fractal antenna.
The electro-forming process exhibits several benefits over the traditional method of producing fractal antennas. The plating mandrel can be re-used up to five hundred times, thus eliminating the photo step for each manufacturing cycle. The amount of hazardous waste is decreased significantly; therefore, the cost of disposing of such waste is greatly reduced, as are the environmental consequences. The relatively low cost of the mounting substrate also provides a cost benefit over the previous technique.