Questions answered in this blog:
1. What is the signal frequency of the major GNSS systems?
2. Why do all major GNSS systems choose those frequencies to broadcast signals?
1. Common signal frequencies of major systems
- GPS
| System band name | band | Frequency/MHZ |
|---|---|---|
| L1 | 1 | 1575.42 |
| L2 | 2 | 1227.60 |
| L5 | 5 | 1176.45 |
- Galileo
| System band name | band | Frequency/MHZ |
|---|---|---|
| E1 | 1 | 1575.42 |
| E5a | 5 | 1176.45 |
| E5b | 7 | 1207.14 |
| E5 (E5a + E5b) | 8 | 1191.795 |
| E6 | 6 | 1278.75 |
- BDS
BDS-2 broadcasts signals B1I, B2I, B3I; BDS-3 broadcasts B1I, B3I, but also B1C, B2a, B2b, B2a+b
| System band name | Frequency/MHZ | band |
|---|---|---|
| B1I | 1561.098 | 2 |
| B2I | 1207.14 | 7 |
| B3I | 1268.52 | 6 |
| B1C | 1575.42 | 1 |
| B2a | 1176.45 | 5 |
| B2b | 1207.14 | 9 |
| B2a + b | 1191.795 | 8 |
- QZSS
| System band name | band | Frequency/MHZ |
|---|---|---|
| L1 | 1 | 1575.42 |
| L2 | 2 | 1227.60 |
| L5 | 5 | 1176.45 |
| L6 | 6 | 1278.75 |
- SBS
| System band name | band | Frequency/MHZ |
|---|---|---|
| L1 | 1 | 1575.42 |
| L5 | 5 | 1176.45 |
Note: These should only be the size of the center frequency, and each frequency band should have a certain width (bandwidth). These are only the frequency bands used for positioning that the author has come into contact with, and there may be other frequency bands . These will be added when the author learns.
It is worth noting that:
- 1575.42MHZ：L1、E1、B1C…
- 1176.45MHZ ： L5 E5a 、 B2a ...
- 1270.14MHZ：E5b、B2I、B2b
- 1191.795MHZ：E5a+b、B2a+b
2. Reasons for choosing this band
That's right, the signals broadcast by the GNSS system are electromagnetic waves like visible light, but its frequency band is not in the visible frequency band of the human eye, so it cannot be seen by the human eye. When electromagnetic waves propagate between the ground and satellites, they are absorbed by free electrons and ions in the ionosphere, and absorbed and scattered by oxygen molecules and water vapor in the troposphere, resulting in energy loss. When the signal is in the frequency band 0.3GHZ~10GHZ(1G=1000M) , the atmospheric loss is minimal. This frequency band is called the "radio window". These "windows" are often considered when selecting satellite communication and navigation frequency bands. Among them, the frequency range of L-band is 1GHZ~2GHZ, the frequency range of S-band is 2GHZ~4GHZ, and the frequency range of C-band is 4GHZ~8GHZ. Among the three bands, the C-band has the highest frequency and the ionospheric delay has the least impact, but the rainfall loss is the most serious; the L-band has the lowest frequency and the ionospheric delay has the largest impact, but is basically not affected by rainfall. At the beginning of the design of the GPS satellite navigation system in the United States, many different frequency bands have been demonstrated, but none of the frequency bands can optimize all design criteria (just as there is no perfect person in the world, there is no perfect thing in the world), choose L Band is the best compromise method that comprehensively considers frequency availability, propagation influence, and system design.
3. About the radar band (extended reading)
This piece refers to
https://blog.csdn.net/wordwarwordwar/article/details/78297760
The author seems to have obsessive-compulsive disorder, and I always want to understand why something is called this name, just like why an L-band is called L-band. Fortunately, a senior made a summary. Here is an excerpt.
There are two sets of standards for the division of electromagnetic wave bands, one is the old standard, and the other is the new standard (it is so simple). The old radio wave band is divided into L、S、C、X、Ku、Ka、W, the above-mentioned L-band is in it. So why is it called L?
It turned out that the old naming rule originated during World War II. The earliest electromagnetic wave wavelength used to search radars was 23cm(1.3GHZ). This band was defined as a Lband (English Longprefix), and later the center wavelength of this band became 22cm. When 10cm(3GHZ)the electromagnetic wave of wavelength is used, its band is defined as the Sband (English Shortprefix, meaning electromagnetic wave shorter than the original wavelength). After the 3cm(10GHZ)emergence of fire control radars that mainly use electromagnetic waves, electromagnetic waves of 3cmwavelengths are called Xbands because they Xrepresent a certain point on the coordinates. In order to combine the advantages of Xbands and Sbands, 5cm(6GHZ)radars with a center wavelength of λ have gradually appeared . This band is called Cband ( Cthat is Compromise, the prefix of the word "combined" in English).
After the British, the Germans also began to independently develop their own radars, and they chose to 1.5cm(20GHZ)be the center wavelength of their radars. Electromagnetic waves of this wavelength are called Kbands ( K = Kurtz, the prefix "short" in German). "Unfortunately", the wavelength chosen by the Germans with the "precision" peculiar to the Germanic nation can be strongly absorbed by water vapor. As a result, the radar of this band cannot be used in rain and foggy weather. In order to avoid this absorption peak, radars designed after the war usually use a Kwavelength that is slightly longer than the band ( Ka, the English K-aboveabbreviation, meaning Kabove the band) and slightly shorter ( Ku, the English K-underabbreviation, meaning Kbelow the band) Band. Finally, since the earliest radars used meter waves, this band is called Pband ( PforPreviousThe abbreviation for "in the past" in English).
The list is as follows:
| Band name | Frequency Range |
|---|---|
| L band | 1 to 2 GHz |
| S band | 2 to 4 GHz |
| C band | 4 to 8 GHz |
| X band | 8 to 12 GHz |
| By the band | 12 to 18 GHz |
| K band | 18 to 26.5 GHz |
| Ka band | 26.5 to 40 GHz |
| Q band | 30 to 50 GHz |
| U band | 40 to 60 GHz |
| V band | 50 to 75 GHz |
| E band | 60 to 90 GHz |
| W band | 75 to 110 GHz |
| F band | 90 to 140 GHz |
| D band | 110 to 170 GHz |
Because the system is very cumbersome and inconvenient to use. It was finally replaced by a wavelength sub-band system divided by actual wavelengths. The conversion of these two systems is as follows.
Original P Band = Current A/B Band
Original L Band = Current C/D Band
Original S Band = Current E/F Band
Original C Band = Current G/H Band
Original X Band = Current I/J Band
Original K Band = Current K band
The radar band represents the frequency (wavelength) range of the emitted electromagnetic wave. Under the condition of non-phased array single radar, the high-frequency (short-wavelength) band is generally more accurate, but the range is short; the low-frequency (long-wave) band has a longer range. , Found that the target distance is large.
- S-band radar is generally used as a mid-range warning radar and tracking radar.
- X-band radar is generally used as a short-range fire control radar.