Most GNSS (Global Navigation Satellite System) receivers have two parts: the antenna and the processing unit or receiver.
The antenna is where the satellite signal is received, and the receiver understands the received information and translates it into measurements that we understand, such as latitude and longitude. In dual-antenna systems, they are often referred to as "primary" and "secondary" antennas. The RT3000 unit shown has two built-in GNSS receivers.
Although GNSS receivers do all the work, the actual measurements they produce are related to the position of the antenna itself. This is important to keep in mind because the length of the antenna cable means that the receiver can sometimes be quite far away from the output position measurement. For satellite navigation and everyday GPS products, this is not important, as their accuracy is rarely able to exceed a few meters.
It is important to realize that calculations regarding position, speed, and altitude are related to the antenna itself, not to the receiver. To understand how GNSS works, we need to divide GNSS into sections and understand each one a little. Since GPS is the most familiar system for people, let's just look at it and divide it into three parts: spatial part, control part, user segmentation.
1. Space part.
The space component deals with satellites in orbit. In 2015, the GPS constellation consisted of 32 non-geostationary satellites in mid-Earth orbit, but not all of them were active. Each satellite orbits every 11 hours, 58 minutes and 2 seconds, with an average altitude of 20,200 km (i.e., an orbital radius of 26,571 km).
The GPS satellite constellation is arranged in six equidistant orbital planes, with no less than four satellites on each plane. This arrangement ensures that at least four satellites can be seen at 15° above the horizon at almost any time and from any point on Earth, although in practice there are usually more.
Although satellites vary in age and design, their operating principles remain the same. Each clock contains four fundamental frequencies of 10A high-precision clock of 23MHz, they continuously transmit two carriers back to Earth at the speed of light in the L-band. These carriers are called L1 and L2.
The frequency of the L1 carrier is 157542mhz (10.23mhz×154=1575.42mhz)。
The frequency of the L2 carrier is 122760mhz (10.23mhz×120=1227.60mhz)。
Carriers are important because they bring information back to Earth from the satellite, and it is this information that allows our receivers to determine where we are;
Second, the control part.
The control part refers to multiple ground stations located around the globe (near the equator) that track, control, and send information to each GPS satellite. This is an important role because the clock synchronization of each satellite is critical – because the entire system relies on timing.
The orbital information sent to each satellite is also crucial because we need it to determine the position of the satellite at the time the information is sent. All this information is sent to the satellite, which is then transmitted to the GPS receiver via L1 carrier navigation messages;
3. User Section.
User segmentation is the part that most people are interested in. This segment includes anyone or anything that has a GPS receiver. Satellite navigation, cell phones, drones, law enforcement. So how does it work?
As we've already seen, there's a constellation of satellites orbiting above our heads, sending a steady stream of information back to Earth at the speed of light. It will take some time to understand how this can help determine our location, but it is based on a process called trilateration.
Before we step in, we should correct a common misconception. The GNSS receiver inside the satellite nav or mobile phone will never send any information to the satellite. The receivers we use today are completely passive – they only receive information. When the Galileo system in Europe is running, its receiver will be slightly different, because there will be an emergency function, which will send a message when activated, but this does not apply to normal operation.
Here's what's happening when you hear people talk about GPS tracking stuff, like armored vehicles. The GNSS receiver on the vehicle is receiving the signal from the satellite and determining its location. Once it knows its location, it sends this information back to a monitoring station using other systems such as a GSM data connection.
The above is the content of how the GNSS antenna generally needs to work for you, I hope you will help after reading it!