Aircraft Design: 5.8Ghz Image Transmission

B站集合（只能电脑端打开）：
https://www.bilibili.com/medialist/play/222849929?from=space&business=space_series&business_id=2724064&desc=1
功能验证视频链接：
https://www.bilibili.com/video/BV1xW4y1J7j2/?spm_id_from=333.999.0.0&vd_source=abc21c793e11e100260f94c90e8d76b1
功率检测 视频链接：
https://www.bilibili.com/video/BV1wg411h7P6/?spm_id_from=333.999.0.0&vd_source=abc21c793e11e100260f94c90e8d76b1
 
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QQ group: 595223820LiChuang platform can upload a maximum of 50M files. If the file is too large, it cannot be uploaded. The original file will be uploaded to the QQ group. If you have any questions, please come to communicate.
 
Basic introduction of the project
This project is mainly to design the 5.8Ghz image transmission of the aircraft to realize the transmission of the camera video signal on the aircraft.
This project mainly includes schematic design, PCB design and circuit simulation. Schematic and PCB design account for up to 30% of the workload of this project. Circuit simulation is a very time-consuming and tedious process.
Why do we need to perform circuit simulation?
5.8Ghz is a high-frequency circuit. In order to effectively transmit the video signal of the camera on the aircraft. Impedance matching must be performed. For impedance matching, this project provides a feasible method, which is simulation.
To do simulation, you must first complete the schematic design, select the impedance matching capacitor and inductor components, confirm the stacking structure, and make a preliminary design of the PCB, and then perform circuit simulation on the preliminary PCB design.
The stacking structure determines the stacking structure set during simulation, which is very important! ! !
This circuit board has 4 layers and the stacking structure is 7628! ! ! ! ! ! (The change of stacking structure will affect the impedance)
Based on my experience in doing this project, the following design process is given, which is ideal. Suppose you want to change the components required for impedance matching, capacitors and inductors, everything starts again...
(So the simulation of high-frequency circuits is time-consuming and cumbersome)
This project gives detailed simulation steps, see the specific design part.
The basic circuit, that is, the interface, is shown in the figure below, mainly including the power supply circuit and the RF + PA circuit. The power supply interface supports 3S and 4S batteries. VIDEO is the video input interface; PDET is the PA output power detection interface.
You can short-circuit the part shown in the figure to select the frequency and select the signal transmission frequency to be used.
The signal transmission frequency that can be selected by shorting is shown in the figure below.
The interface for SPI programming is also reserved for frequency selection.
Through SPI programming, the signal transmission frequency that can be selected is shown in the figure below.
The RFPA5542 PA chip has a 3-stage amplifier circuit. You can short-circuit the part shown in the figure below to choose to use the 1st, 2nd or 3rd stage amplifier circuit.
This circuit board has 4 layers and the stacking structure is 7628! ! ! ! ! ! (The change of the stacking structure will affect the impedance)
This stacking structure also determines the stacking structure set during simulation.
Simulation results of two transmission lines:
S parameter
VSWR
Electromagnetic
field physical test of the top layer:
5.8G image transmission installation diagram
Front of circuit board
Back of circuit board
Overall diagram
Function verification picture:
Power detection picture:
Use RF power meter and external 30db signal attenuator.
Using two-stage amplification and external 30db attenuator, the signal transmission power is:
-13+30=17dbm=50mW
-10+30=20dbm=100mw
Using two-stage amplification, the signal transmission power is between 50~100mw.
Using third-order amplification and an external 30db attenuator, the signal transmission power is:
-2+30=28dbm=640mW
-3dbm+30=27dbm=500mW
Using two-order amplification, the signal transmission power is between 500~640mw.
B station collection (can only be opened on the computer):
https://www.bilibili.com/medialist/play/222849929?from=space&business=space_series&business_id=2724064&desc=1
Function verification video link:
https://www.bilibili.com/video/BV1xW4y1J7j2/?spm_id_from=333.999.0.0&vd_source=abc21c793e11e100260f94c90e8d76b1
Power detection video link:
https://www.bilibili.com/video/BV1wg411h7P6/?spm_id_from=333.999.0.0&vd_source=abc21c793e11e100260f94c90e8d76b1
 
 
Let me insert a message. The ESC and flight control I made for the previous LiChuang Competition are the ones on this quadrotor.
ESC: https://diy.szlcsc.com/p/CLZ1/ji-yublheli-diescFlight
control: https://diy.szlcsc.com/p/CLZ1/f405-fei-kongSpecific
 
design part
Aircraft design 5.8Ghz image transmission Contents
1. 5.8Ghz image transmission 11
2. Principle: amplifier working state, bias network and impedance matching 11
3. Schematic diagram and PCB design 14
4. PCB simulation: HFSS 3D Layout 16
4.1 PCB1 simulation steps 16
4.2 PCB1 simulation results 41
4.3 PCB1_1 simulation results 45
4.4 PCB1_2 simulation results 48
4.5 The simulation results of PCB1_1 are better than those of PCB1 and PCB1_2. Why didn't you use PCB1_1? 49
5. Physical test 50
6. Notes 52
1. The image transmission of the 5.8Ghz image transmission
aircraft includes two parts: sending and receiving. This project is about the image transmission transmission part; its main function is to transmit the video signal of the camera on the aircraft.
At present, the mainstream 5.8Ghz image transmission chips are basically RTC6705. The schematic diagram of RTC6705 can also be found on the Internet. However, for someone who has just come into contact with high-frequency signals, it is difficult to make a functioning image transmission even with a schematic diagram, so many people are discouraged.
I will explain the principle based on my own understanding. If there is anything wrong, I hope you can point it out and make progress together.
2. Principle: The working state of the amplifier, the paranoid network and the impedance matching
principle part, refer to Section 8.3 of "RF Circuit Design - Theory and Application" on the working state of the amplifier and the paranoid network, and explain it to you. I will also upload this book as an attachment.
Mainly look at 8.3.2 Bipolar transistor bias network. Refer to the following figure for explanation.
The following figure is the logic diagram in the RTC6705 data sheet.
RFout in the book is PAOUT1 and PAOUT2 of RTC6705. Comparing the two figures, we can see that we need to select appropriate RFC (radio frequency choke), CB and R4 outside PAOUT1.
Mainly introduce RFC (radio frequency choke): RFC is an inductor. We all know that inductors pass DC and block AC. In this circuit, this function of the inductor is fully reflected. After VCC (DC voltage) passes through R4 and RFC, it provides the transistor with appropriate voltage and current. For the high-frequency signal (AC) coming out of RFout, RFC is equivalent to a circuit breaker.
The high-frequency model of the inductor is shown in the figure below. At a certain frequency, the inductor will self-resonate, and its self-resonant frequency is called SRF.
In the application of chokes, SRF can most effectively block the frequency of the signal. At frequencies below SRF, the impedance increases with increasing frequency. At SRF, the impedance reaches its maximum value. At frequencies above SRF, the impedance decreases as the frequency decreases. As shown in the figure below.
Therefore, in an ideal state, an inductor with a self-resonant frequency slightly greater than the highest frequency of the signal should be selected. In this ideal state, an inductor with a self-resonant frequency of 6Ghz can be selected.
CB is a DC blocking capacitor, which passes AC and blocks branch currents. The AC signal that is not blocked by the RF choke is directly grounded. CB 20pF, R4 10ohm. (The size of CB and R4 is not the key point. The important thing is the selection of the RF choke and making the impedance of the transmission line 50ohm)
It can also be 10pf, 0ohm. Understanding its role in the circuit is the most important thing.
The most important thing about impedance matching is to know the output impedance of the signal source.
The figure below is the original words in the data sheet of RTC6705. Before filtering, there is proper matching at the output of the PA. The output impedance should be 50ohm.
The input and output impedances of the RFPA5542 PA are both 50ohm.
So we need to make the impedance of the transmission line 50ohm, that is, the two transmission lines shown in the figure below.
 
This requires the use of HFSS 3D Layout for simulation.
3. Schematic diagram and PCB design
See the design drawing section.
Note:
The width of the transmission line should remain unchanged, so that the pad width and the transmission line width are consistent. This makes it easier to do impedance matching.
The width of the transmission line in this project is 0.3mm.
The impedance is about 56ohm.
4. PCB simulation: HFSS 3D Layout
First, using HFSS 3D Layout for simulation requires ODB++ format files or other formats (I use ODB++ format files). EasyEDA cannot export directly, so you can only use EasyEDA to export Altium Designer format files first, and then use Altium Designer to export ODB++ format files.
Give the detailed simulation steps of PCB1, as well as the simulation results of PCB1_1 and PCB1_2.
4.1 PCB1 simulation steps
1. Export the PCB file in EasyEDA to a file in Altium Designer format
2. Unzip the exported file and open it with Altium Designer;
3. After importing, it is found that the copper coating is gone, and the two middle copper layers are gone; add the two middle copper layers, re-copperize, and define the template. After processing, it is as shown in the figure below.
4. Export the file in ODB++ format, and operate as follows;
5. Only the top layer, bottom layer, two middle layers and mechanical layer 1 need to be exported; only the save operation is left, which will not be shown.
6. Open Ansys Electronics Desktop and import the file in ODB++ format;
7. Import the PCB1.tgz file generated when generating the ODB++ format file, and click OK.
8. Then click OK.
9. After importing, it is as shown in the figure below. Click Save to save.
10. Click here to set the display format;
11. Set it according to your own preferences, I like to set it to Display Solid;
12. After the setting is completed, the effect is as shown in the figure below;
13. Click here to set the stacking structure;
14. Set it to the stacking structure of Jiali Chuang, the stacking structure of Jiali Chuang is as follows;
15. Set thickness to the thickness of Jiali Chuang's stacking, and set each layer to display (that is, the front column, check it);
16. After the setting is completed, click Apply and Close; the effect is as shown in the figure below;
17. Click HFSS Extents and Edit in turn, as shown in the figure;
18. Set Horizontal and Positive to 30mm; Click OK
19. Click HFSS Extents and Show in turn, as shown in the figure;
20. Reduce the page appropriately and adjust the appropriate position, as shown in the figure; squares, these are the two 30mm set just now; HFSS 3D Layout simulation must be carried out in a limited space, and the limited space set is shown in the square in the figure below.
21. Click HFSS Extents, Hide, as shown in the figure; hide the limited space you set (it just cannot be seen, but it still exists. It is OK not to hide it. I personally like to hide it)
22. Click Orient, Fit All; the effect after clicking is as shown in the figure, that is, the circuit board is square, which is easy to operate.
23. Click View, Components; 24. The components and chips on the circuit board will be displayed on the right;
25. Click IC and RTC in turn; right click on RTC and click Create Ports On Component;
26. Select $1N154240 on the pop-up page; 27. Click EM Design;
28. Set HFSS Type to Gap; as can be seen from the figure below, the default Port is 50ohm;
29. ​​Repeat 25-28 and set $1N59286, $1N154747, and $1N103981 as Ports, and the positions are as follows;
30. The figure below is a side shot of the completed settings;
31. Select the 6.8nH inductor and click Model Info;
32. Select Library;
33. Click Library Browser;
34. Find the selected inductor model (LQW15AN6N8G00D) on the pop-up page, its self-resonant frequency is about 11Ghz, and the self-resonant frequency 6Ghz given below in the LiChuang Mall is the Self Resonant Frequency (GHz) in the data sheet. min.) Click Apply, click OK;
(I thought the self-resonant frequency 6Ghz given below the LiChuang Mall was its self-resonant frequency, which is actually Self Resonant Frequency (GHz min.); when I was screening components, I searched directly for 6Ghz and selected it. I didn’t pay attention to it during simulation. Later I found that the self-resonant frequency was about 11Gh, but the simulation result was also OK, so I continued to use it. The self-resonant frequency of PCB1_1 simulation was 6Ghz, but that component was out of stock);
35. Similarly, set the two 10pF capacitors to the selected model; click Apply, click OK;
36. Click in sequence, as shown in the figure;
37. On the pop-up page, set the frequency to 5.8G and click Confirm; 38. Set the sweep frequency to 5.3-6.3Ghz and click Confirm;
39. Click HFSS 3D Layout and Validation Check in sequence;
40. If there is no error, there is basically no problem with the simulation settings;
41. Click Setup1, right click, and click Analyze to start the simulation.
42. In the Progress status bar below, you can see the simulation progress. Wait for the simulation to complete.
43. When the frequency sweep is completed, the simulation is over and you can view the results.
44. The simulation is about the loss, impedance and standing wave ratio of the two transmission lines.
4.2 PCB1 simulation results
45. Right click on Results and follow the steps below.
45. In the pop-up page, select
dB(S(RF1.1.$1N103981
,U1.13.$1N154747)); dB(S(U1.13.$1N154747,U1.13.$1N154747));
dB(S(U1.3.$1N59286,U3.35.$1N154240));
dB(S(U3.35.$1N154240,U3.35.$1N154240)); and click New Report;
46. The simulation results are shown in the figure below;
It can be seen from the figure that at 5.7-5.9Ghz, the two lines S11 are less than -25dB; at 5.7-5.9Ghz, S21 is basically 0. (The two lines of S21 overlap)
47. Right-click on Results and follow the steps below; 48. Select S(U1.13.$1N154747,U1.13.$1N154747); S(U3.35.$1N154240,U3.35.$1N154240) on the pop-up page ; and click New Report; 49. The simulation results are shown in the figure below; It can be seen from the figure that at 5.8Ghz, the real part of the impedance of the two transmission lines is above 45ohm and below 55ohm. 50. Right click on Results, and follow the steps below; 51. Select VSWR on the pop-up page; VSWR(U1.13.$1N154747); VSWR(U3.35.$1N154240); and click New Report; 52. The simulation results are shown in the figure below; As can be seen from the figure, at 5.7-5.9Ghz, the VSWR of the two transmission lines is less than 1.11. 4.3 Simulation results of PCB1_1 1. The simulation is the loss, impedance and VSWR of these two transmission lines; 2. The 6.8nH inductor is selected as LQG15WZ6N8J02 (LiChuang Mall currently has no stock, so LQW15AN6N8G00D, that is, the 6.8nH inductor in PCB1) with a self-resonant frequency of about 6Ghz. The inductors and capacitors on the remaining transmission lines are ideal inductors and capacitors. 3. The simulation results are shown in the figure below; it can be seen from the figure that at 5.7-5.9Ghz, the two lines of S11 are both less than -36dB; at 5.7-5.9Ghz, S21 is basically 0. (The two lines of S21 overlap) 4. The simulation results are shown in the figure below; it can be seen from the figure that at 5.8Ghz, the real part of the impedance of the two transmission lines is about 50ohm. 5. The simulation results are shown in the figure below; it can be seen from the figure that at 5.7-5.9Ghz, the standing wave ratio of the two transmission lines is less than 1.04. 4.4 PCB1_2 simulation results Animate_log figure 4.5 PCB1_1 has better simulation results than PCB1 and PCB1_2, why not use PCB1_1? Because: A. The 6.8nH inductor (LQG15WZ6N8J02) is out of stock. If it is available, it can be made again; B. In the simulation of PCB1_1, the inductors and capacitors on the two transmission lines are ideal components. They are not used in the specific component library like PCB1 and PCB1_2. There must be a deviation between the simulation result and the actual result. I don’t know whether it will be better or worse than the actual result. If it is worse than the actual result, it will be directly G; C. Selecting components and running simulation is a very tedious process. At present, there are dozens of G files of simulation files, whether good or bad. The simulation can really run for a day and a night. D. Provide an idea for friends who like and are interested. You can try it yourself. 5. Physical test 5.8G image transmission installation picture Front of circuit board Back of circuit board Overall picture Function verification picture: Power detection picture: Use RF power meter and external 30db signal attenuator.
































Using two-stage amplification and an external 30db attenuator, the signal transmission power is:
-13+30=17dbm=50mW
-10+30=20dbm=100mw
Using two-stage amplification, the signal transmission power is between 50~100mw.
Using three-stage amplification and an external 30db attenuator, the signal transmission power is:
-2+30=28dbm=640mW
-3dbm+30=27dbm=500mW
Using two-stage amplification, the signal transmission power is between 500~640mw.
B station collection (can only be opened on the computer):
https://www.bilibili.com/medialist/play/222849929?from=space&business=space_series&business_id=2724064&desc=1
Function verification video link:
https://www.bilibili.com/video/BV1xW4y1J7j2/?spm_id_from=333.999.0.0&vd_source=abc21c793e11e100260f94c90e8d76b1
Power detection video link:
https://www.bilibili.com/video/BV1wg411h7P6/?spm_id_from=333.999.0.0&vd_source=abc21c793e11e100260f94c90e8d76b1
 
 
I’ll insert a message. The ESC and flight control I made in the previous LiChuang Competition are on this quadcopter.
ESC: https://diy.szlcsc.com/p/CLZ1/ji-yublheli-diesc
Flight control: https://diy.szlcsc.com/p/CLZ1/f405-fei-kong
 
6. Notes
1. The book "RF Circuit Design - Theory and Application" is too big, 116M, and cannot be uploaded. The maximum upload size is 50M. I only uploaded the working status of the amplifier and the paranoid network in Section 8.3.
2. The original HFSS 3D LAYOUT simulation file is over 600M, and after compression it is still over 400M, so there is no way to upload it directly. Here is the network disk link.
Link: https://pan.baidu.com/s/1fEJYfRwdB43qmpmRgGhqow
Extraction code: 30hl
3. Personal contact information QQ: 2995001663 QQ group: 595223820 This platform can upload a maximum of 50M files. If the file is too large, it cannot be uploaded. The original file will be uploaded to the QQ group. If you have any questions, please feel free to communicate.
4. I hope you will support me by liking, commenting and collecting.