Classification and important functions of GPS antennas

　　The function of the GPS receiving antenna is to convert the electromagnetic wave energy of the radio signal from the satellite into the current that the receiver electronic device can ingest and apply. The size and shape of the antenna are important because these characteristics determine the antenna's ability to pick up weak GPS signals. As required, the antenna can be designed to work on a single L1 frequency, or it can work on two frequencies, L1 and L2. Since GPS signals are circularly polarized waves, all receiving antennas are circularly polarized. Despite various constraints, there are still many different antenna types, such as monopole, dipole, helical, quadrifilar helical, and microstrip antennas.

　　There are generally two types of built-in antennas for GPS receivers we see on the market - flat-panel antennas and four-armed helical antennas. What are the advantages and disadvantages of the two antennas? Let us answer them for you.

　　1.. Patch Antenna

　　Panel antennas are the most common type of antenna due to their durability and relative ease of fabrication. Its shape can be round, square or rectangular, like a copper-clad printed circuit board. It consists of one or more pieces of metal, so the most common shape for GPS antennas is a lumpy knot, like a biscuits. Since the antenna can be made small, it is suitable for aerospace applications and personal handheld applications.

　　Another major characteristic of an antenna is its gain pattern, or directivity. Using the directivity of the antenna can improve its anti-dry and anti-multipath ability. In precise positioning, the stability of the phase center of the antenna is a very important index. However, in ordinary navigation applications, people hope to use an omnidirectional antenna to receive at least the visible satellite signals in all the sky within a five-degree field of view above the antenna horizon, but when the flat-panel antenna is directly above the satellite, the signal gain is the largest. , there are two problems:

　　1. The receiving range of the tablet is above the tablet, and the tablet should face the sky, which will bring trouble to hand-held and vehicle-mounted. We can see that there are more and more CF receivers with adjustable angles (foldable SDGPS), because the tablet The characteristic of the type antenna makes the manufacturer come up with a trick for the receiver to have a better reception effect.

　　2. We know that although the satellite signal above our head is better and easier to lock, the satellite above is actually the most useless. If there is no low-angle satellite, the error will be relatively high, and the accuracy will be very high. Difference. So based on these shortcomings, four-arm helical antennas have also been used on GPS receivers.

　　2. Quadrifilar Helix Antenna

　　A four-armed helical antenna consists of four specially curved metal lines. No grounding is required. It has the characteristics of a Zapper antenna, and also has the characteristics of a vertical antenna. This ingenious structure makes the antenna gain 3dB in any direction, increasing the time for satellite signal reception. The four-armed helical antenna has a full 360-degree receiving capability, so when combined with the pda, the four-armed helical antenna can receive regardless of the placement position of the PDA. Good reception limits. Using this kind of antenna, when the satellite appears 10 degrees above the ground level, the signal transmitted by the satellite can be received.

　　However, if there are many interference sources near the ground receiving station, the four-armed helical antenna is not suitable, because the four-armed helical antenna has a gain in the horizontal direction, which will amplify the noise and interfere with the reception of satellite signals. However, technology is advancing, and the four-arm helical antenna produced today can break through many of the limitations of traditional antennas. The antenna is made of ceramic, and the Near-Field is extremely small, only about 3~5mm, while the Near-Field of some traditional antennas is even as high as 1m. The smaller the Near-Field, the less human body will cause interference when the user holds the GPS device. The current quadrifilar helical antenna also features a complete balun circuit (Balun) design, which isolates the noise around the antenna, thus allowing antennas of various functions to coexist in a very small space without interfering with each other . The importance of this feature is indescribable for handheld electronic products with increasingly diverse integration functions and emphasis on light, thin, and short.

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