The uses for antennas continue to increase with reductions in antenna size and cost, and the development of complimentary microwave designs. For size reduction, "patch" antennas are of particular interest.
Patch antennas generally comprise a dielectric substrate, an electrically conductive ground layer disposed below the dielectric substrate, and an electrically conductive patch antenna element disposed over the dielectric substrate. The patch antenna element may be coupled to an RF feed means using any of several conventional methods such as a coaxial cable. A multiple frequency antenna may be constructed by "stacking" patch elements with intermediate dielectric layers.
Traditionally, efforts have been made to utilize dielectric materials having dielectric constants as close as possible to that of the free space into which the antenna radiates (e.g. approximately K=1.0 for air). Dielectric materials used in thin-film patch antennas have typically had a relatively low dielectric constant (e.g. approximately K=2 to 3), as is the case where a Teflon-fiberglass composite substrate is used. More recently, ceramic substrates having a dielectric constant of about 9 to 10 have been proposed for patch antennas in order to achieve size reduction.
For many expanding antenna applications, reception and transmission of high frequency signals is required. A primary example of growing importance is Global Positioning System (GPS) receivers. Such receivers are used, for example, in surveying and navigation applications. GPS receivers typically operate in the L1 and/or L2 bands, which are centered on approximately 1.575 GHz and 1.227 GHz, respectively, and preferably exhibit low-angle gain characteristics. Given the inherently mobile nature of many GPS antenna applications, reduced antenna size is desirable. Such size reduction is particularly useful in cases where GPS receivers are hand carried.
A mobile GPS transceiver is potentially capable of accessing, via satellite transmission, most data that is presently carried by fixed lines. Sufficient cost reduction can ultimately yield widespread use of mobile GPS transceivers and data access. Further, such cost reduction will allow for mobile communications between remote locations not served by fixed line transmission networks, including for example, communications within a fleet of mobile units.
Cost reduction may be achieved by reducing material and production costs. A reduction in antenna size correspondingly reduces material requirements. In patch antennas, the size of the antenna patch element may be reduced by increasing the dielectric constant of the dielectric which separates the antenna patch element from the ground plane. However, in order to accomplish simultaneous size and cost reduction, the higher dielectric constant must be achieved though use of materials and production methodology that does not disproportionately increase overall costs.