The function of the GPS receiving antenna is to convert the electromagnetic wave energy of the radio signal from the satellite into a current that can be picked up by the receiver electronics.

　　The size and shape of the antenna are very important, because these characteristics determine the ability of the antenna to acquire weak GPS signals. According to needs, the antenna can be designed to work on a single L1 frequency, or on two frequencies, L1 and L2. Since GPS signals are circularly polarized waves, all receiving antennas work in circular polarization. Despite various constraints, there are still many different antenna types, such as monopole, dipole, spiral, four-arm spiral, and microstrip antenna.

　　There are generally two types of built-in antennas for GPS receivers that we see on the market-flat antennas and four-arm helical antennas. What are the advantages and disadvantages of the two antennas? Let's take a look.

　　Flat antenna

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

　　Another main characteristic of the antenna is its gain pattern, namely directivity. Using the directivity of the antenna can improve its anti-interference and anti-multipath effects. In precise positioning, the stability of the phase center of the antenna is a very important indicator. However, in ordinary navigation applications, people hope to use an omnidirectional antenna to receive at least all visible satellite signals in the sky within five degrees above the horizon of the antenna. However, the signal gain of the flat antenna is the largest when the satellite is directly above the antenna. , There are two problems:

　　1. The receiving range of the tablet is above the tablet, and the tablet needs to face the sky. This will cause trouble for both handheld and vehicle. We can see that more and more adjustable angle CF receivers are due to the characteristics of the flat antenna. Manufacturers came 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, in fact the satellite above our head is the most useless. If there is no low-angle satellite, the error will be relatively high and the accuracy will be very high. difference. Therefore, based on these shortcomings, four-arm helical antennas are also used on GPS receivers.

　　Four-arm helical antenna

　　The four-arm helical antenna is composed of four specifically curved metal lines. No grounding is required. It has the characteristics of a Zapper antenna as well as a vertical antenna. This ingenious structure enables the antenna to have a gain of 3dB in any direction, which increases the time for satellite signal reception. The four-arm helical antenna has a full 360-degree receiving capability. Therefore, when combined with a PDA, no matter how the PDA is placed, the four-arm helical antenna can receive it, which is different from using a flat-panel GPS antenna. The limits of good reception. Using this 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-arm helical antenna is not suitable, because the four-arm helical antenna has a horizontal gain, which will amplify the noise together and interfere with the reception of satellite signals. However, technology is advancing, and the four-arm helical antennas now produced can break through the limitations of many 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 the human body will cause interference when the user holds the GPS device. The characteristics of the current four-arm helical antenna also include a complete balun circuit (Balun) design, which can isolate the noise around the antenna, so it can allow antennas with various functions to coexist in a very small space without mutual interference . The importance of this feature is indescribable for the increasingly diverse integrated functions and the emphasis on light, thin and short handheld electronic products.

　　As you see here, you probably also know the benefits of the four-arm helical antenna, but the price of the four-arm helical antenna is still relatively high, so most GPS receivers using this antenna are in the handheld High-end products, relatively expensive, are suitable for consumers who like handhelds and users who have strict requirements for positioning time. The flat-panel antenna has acceptable performance and low price, which is more suitable for general consumers.