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A GPS antenna is a device that helps boost the reception signal to a GPS unit, whether it is a standalone unit or an embedded unit. Often a GPS antenna is used in a situation where the GPS unit itself is somehow removed from a line of sight to the sky, as in a car, to help the GPS “see” the sky without having to be moved. GPS antennae may be purchased for a range of budgets, or cheaper home versions can be made with fairly common components.
GPS, or the Global Positioning System, is a satellite system originally developed by the United States Department of Defense. It utilizes more than two dozen satellites orbiting the Earth to allow receivers on the ground or in the sky to tell exactly where they are, by receiving heads off of multiple satellites. Using this location, devices can detect not just latitude and longitude, but also altitude, and even heading and speed. For years, GPS was reserved for military use in the United States, but following a directive by President Reagan in 1983 it became open for civilian use.
Civilian GPS contains certain restrictions, imposed by the US government to make sure hostile forces don’t use the technology in missiles. As a result, consumer GPS isn’t capable of operating when moving at more than 515 m/s at more than 60,000 feet (18 km). Throughout the eighties and early nineties GPS was used primarily in commercial avenues, such as on fishing boats, in airplanes, or for geographic surveying. In the late nineties it began gaining popularity for consumers for hiking or for driving, and by the new millennium cars were being equipped with built-in GPS to give driving directions, and cell phones began having included GPS for directions and location.
A GPS unit has a built in antenna, which is usually quite small and located inside of the unit. While this will likely function in ideal circumstances, such as when in a desert moving at slow speeds or staying still, it may not work as well as one would like in more trying circumstances. A GPS unit likes to have a clear, unobstructed view of the sky, to best receive the microwave signals that allow it to communicate with satellites. For GPS units inside of cars, this can be problematic, so often an external GPS antenna will be used, mounted to the outside of the car with a magnet, and connected to the unit itself by a cable.
In situations such as heavy canopy cover while hiking, the small GPS antenna built into a consumer unit also may not be able to ideally communicate with the satellites. In this case, a larger, more advanced GPS antenna helps the unit overcome the environmental challenges, to give a clear signal. Similarly, moving at high velocities can overwhelm a smaller, less sophisticated antenna, and an external device can boost the signal.
There are a number of different types of GPS antennae, with the patch and Quad Helix styles being the most popular. Both are roughly equal in efficacy, although many people find the quad helix to have a slight bit more sensitivity. Other types of antennae include microstrips, of which the patch is one configuration, planar rings, and spiral helices.