What parameters does external GPS antenna needs to pay attention to

What parameters does External GPS Antenna needs to pay attention to
GPS receiving antenna, electromagnetic energy is converted to a satellite radio signal to the receiver electronics ingestible current applications. The size and shape of the antenna is very important, because these characteristics determine the ability of the antenna can get a weak GPS signal. If necessary, the antenna can be designed to work on a single L1 frequency, also it can work on two frequencies L1 and L2. Because GPS signals are circularly polarized waves, so all receive antennas are circularly polarized work. Although there are a variety of conditions, there are still many different antenna types exist, e.g. unipolar, bipolar, spiral, quadrifilar helical, and the microstrip antenna.
The market saw a GPS receiver built-in antennas are generally two - plate antenna and four arm helical antenna.
Flat antenna due to its durability and relatively easy to make, so became the most common type of antenna. Its shape can be round or rectangular can also be square, as a copper printed circuit boards. It consists of one or more metal sheets constituted, so the most common shape is a GPS antenna junction block, like biscuits. Since the antenna can be made small, and therefore suitable for aerospace applications and personal handheld applications.
Another major characteristic of the antenna, its gain pattern, i.e., directivity. The use of directional antennas to improve its anti-dry and anti-multipath capability. Precise positioning, antenna phase center stability is a very important indicator. However, the general navigation applications, it is desirable to use an omnidirectional antenna capable of receiving at least all the sky within five degrees above the horizon antenna Vision visible satellite signal, but when the flat-panel antenna above the satellite antenna, the signal gain is the greatest , which has two problems:
1, the reception range of the flat top of the plate, the plate must face the sky, which for handheld and car will bring trouble, we can see that CF adjustable angle of the receiver more and more, it is because of this feature makes the flat antenna The receiver manufacturers in order to have better reception effect was thought out move.
2, although the satellite signal that we are on top of the head is better, easier to lock, but in fact satellites are overhead is the most useless, if not low angle of the satellite, the error will be relatively high, the accuracy will be poor. Therefore, based on these shortcomings, the GPS receiver can start using the quadrifilar helical antenna.
Quadrifilar helical antenna consists of four specific bent metal lines formed. Without any grounding. It has had Zapper antenna characteristics, but also with vertical antenna characteristics. Such ingenious structure, so any direction of the antenna has a gain of 3dB, increasing the time the satellite signal reception. Quadrifilar helical antenna has a full 360 degrees to the reception, so when combined with the PDA, PDA regardless of placement, the four-arm spiral antenna Jieneng received is different from the use of flat GPS antenna needs to relatively flat The good restriction received. The use of such antennas, when the satellite appeared in the ground plane 10 degrees, you can receive the signal transmitted by satellite.
If the ground station near sources of interference more quadrifilar helical antenna is not applicable because the quadrifilar helical antenna with a horizontal direction of the gain will amplify noise together, but interferes with the reception of satellite signals. However, advances in science and technology, and now the production of four-arm spiral antenna can break out a number of conventional antennas. The antenna is made of ceramic, Near-Field is extremely small, only about 3-5mm, and some conventional antennas Near-Field even up to 1m. Near-Field smaller, hand-held GPS device when the user, the more the body will not cause interference. Features now four-arm spiral antenna also includes complete balun circuit (Balun) design, this design can isolate the noise surrounding the antenna, so the antenna can allow the coexistence of various functions in a very small space without interfering with each other . For integration increasingly diverse, and emphasize slim and light handheld electronic products, the importance of this feature of the ineffable.