The sensitivity of GPS antenna will be a great impact on its shape. GPS signals are due to the circular polarization wave, the GPS receiver antenna must also adopted circular polarization of the methods of work. GPS can be used for the antenna types, including Patch, Helix / Spiral and PIFA, among which Patch and Helix are the most applications.

              Figure 4 GPS antenna types

Flat antenna lower cost, durability and high production is relatively easy, but its direction is obviously one of the shortcomings. Directional antenna to the plate for the sky to get a better reception, the application must be extremely restricted. In addition, the accuracy of flat-panel antenna is not very stable, although its smooth to receive the satellite signals are at the top, if not the low point of access to the satellite information, the error will be relatively high.

Quadrifilar Helix Antenna with a 360-degree ability to receive all directions so that the antenna in any direction are 3 dB gain, the GPS receiver can be placed in a variety of angles, but also to receive the low point of Satellite signal, which is flat compared to the advantages of the antenna. In addition, Balun circuit design is a better approach, the advantage is to be effective antenna isolation around the noise and allow the coexistence of various functions of the antenna in a very small space and will not interfere with each other, the size of the request for holding a high Equipment is suitable for antenna design, but Helix antenna compared with the high cost of flat-panel antenna, is one of its shortcomings.

Forward-looking technology 1: DR position calculation
DR (Dead Reckoning) technology, mainly used for GPS satellite signal reception difficult occasions. GPS systems to receive satellite signals needed to achieve positioning and navigation functions, and in bad signal or signal shielding the larger environment, such as underground rooms, caves, tunnels, streets and other forest of skyscrapers, GPS systems can not be fully received signal . At this point need the help of DR.

DR GPS technology could be used as the supplementary temporary navigation tools, its principles and is calculated by measuring the distance and direction, such as the physical impact of displacement to projected changes in the relative position of vehicles. General linear distance by Odometer or Accelerometer for measurement; a high degree of change needed Barometer, and other devices, and magnetic Compass, Gyrometer or Differential Odometer is used to measure rotation angle.

As DR obtained by calculating the location information, although in a short period of time in its accuracy is very high, even higher than that of GPS; but a longer time, due to the cumulative impact of the errors, its navigation and positioning accuracy of significant decline. Then re-use GPS systems to find the absolute position, in order to re-use DR. DR and are complementary to each other automotive GPS navigation system, and the high degree of accuracy the location can not simply rely on the DR. At present the DR sensor accuracy, cost, and with the navigation systems integration algorithms, such as the impact of development and commercialization of DR products still small.