LoRa/LoRaWAN tutorial 42: Monopole Antenna and Ground Plane
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- เผยแพร่เมื่อ 2 มิ.ย. 2024
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This is part 42 of the LoRa/LoRaWAN tutorial.
In this tutorial I will explain what a monopole antenna is and why a ground plane is needed.
A ½λ dipole antenna has two elements (each element L = ¼λ), but a monopole antenna has only one element (L = ¼λ).
A monopole antenna relies on a good conducting plane for its operation.
This plane is used as a mirror to create a "second imaginary" element.
The ground (earth) is a conductor and RF energy is reflected from the ground.
The monopole antenna performance can be improved by using a plane made of a better conductive material instead of using the earth itself.
This conducting plane is called the ground plane or counterpoise.
The ground plane must have a radius greater than ½ wavelength from the base of the monopole antenna.
For a ¼λ monopole antenna the reflected radiation from the ground is in phase with the direct radiation.
The receiving antenna (RX) gets energy from the direct path AND from the reflected path which is in phase.
A ¼λ monopole antenna will have twice the gain (3 dB) of a ½λ dipole antenna (in free space).
A ½λ dipole antenna has a gain (G) of 1.64 and an impedance (Z) of 73 Ω at its centre, which is the radiation resistance.
A ¼λ monopole antenna has a gain (G) of 2.15 + 3 = 5.15 dBi (or 3 dBd) and a radiation resistance of 0.5 x 73 = 36.5 Ω when positioned over a large conductive ground plane.
½λ dipole antenna 4NEC2 card deck:
www.mobilefish.com/download/l...
¼λ monopole antenna 4NEC2 card deck:
www.mobilefish.com/download/l...
By default a monopole antenna will perform poorly without the use of a ground plane.
A ground plane can be a network of horizontal wires or a metal plate.
More information about the end node, see:
www.mobilefish.com/developer/...
The end node uses the MCCI LoRaWAN LMIC Library:
github.com/mcci-catena/arduin...
The end node uses the following sketch:
www.mobilefish.com/download/l...
One or more gateways were able to receive my transmitted sensor data, see:
drive.google.com/open?id=18SK...
The logged data can be found at:
www.mobilefish.com/download/l...
www.mobilefish.com/download/l...
A ¼λ monopole without ground plane has a bad antenna performance.
A ¼λ monopole with ground plane with a radius GREATER than ½λ has a good antenna performance.
As demonstrated using a metal plate (radius greater than ½λ) or radials as the ground plane produces approximately the same result.
Using radials is often preferred:
- The radials are lighter than a metal plate.
- The radials are cheaper than a metal plate.
- The radials are more resistant to weather conditions (wind, rain).
When using a metal plate or radials as a ground plane, in both cases the impedance is around 75Ω instead of 50Ω.
When radials are used, bend it to a certain angle and the impedance will be 50Ω and the VSWR will remain below 2.
The effect of a ground near any antenna (for example: monopole, dipole, Yagi-Uda, Moxon, etc) can be significant.
The antenna performance can be positive or negative.
The effect can be simulated using an antenna modelling software (see tutorial 38).
Check out all my other LoRa/LoRaWAN tutorial videos:
• LoRa/LoRaWAN tutorials
Subscribe to my TH-cam channel:
/ @mobilefish
The presentation used in this video tutorial can be found at:
www.mobilefish.com/developer/...
#mobilefish #lora #lorawan - วิทยาศาสตร์และเทคโนโลยี
Really good video and very well explained.
Thank you so much, this content is perfect. I will make time to watch and study all the tutorials. Greetings from north Africa ( Algeria)
damn using that piece from within the old electical clamp is genius. made my day cause my antenna is now working (my solder-joint was trash)
Sir you are excellent your explanation is very nice
Regards
Dr Shukla
Thank-you so much for this and the other videos in the series. The subject is clearly explained and it is good to be able to pause the video to look at the data and think about them before moving on.
Amazing video tgank you very much!
Just discovered your Channel and Suscribed. Thank you and complements on the teaching style. ...73
What a amazing channel!
THANK YOU SO MUCH , VERY INFORMATIVE VIDEO
Hi, thanks for your videos, they help me to learn a lot more on antennas and RF :)
If the RSSI levels in Rx are roughly the same, what may explain the difference in time to receive 15 messages (monopoles taking more time)?
I have an hypothesis, that is: when you do the average RSSI calculation, only the received packets (which have sufficiently good RSSI and SNR) are being taken into account, what can give the false impression that the power received is roughly the same for both antennas. In this case, I'm assuming that the received RSSI is close to the sensitivity limit.
Does that makes sense?
Thanks again for the content you publish!
Hi, thanks for your video, I learnt a lot, I see Raymond point out a mistake in your video, is the lmba/4 ground plane result still correct?
I think perhaps the ground plane of the LoRa board is better than you think. I bet if found the PCB details you’ll find the board has 2 layers of copper . One layer as a VSS ground plane coupled to vcc and one layer as the reflective ground plane for the monopole. Excellent video! Thanks for all the time you put into making it.
Amazing explanations in all your videos!!
I do have a (potentially dumb) question, but can water act as the ground plane? I'm asking because I've built a water quality monitoring buoy which sends data via LoRaWAN to my own gateway. It worked okay during testing while it was nearby at a dock, but for my next test it is located in the middle of a bay and seems not to connect unless you get very close to it. I'm realizing from your videos that the dipole antenna provided by Arduino is mounted in the wrong orientation, but I will fix that. But I'm wondering if I could somehow use the water itself as the ground plane, since it's floating in water, and water is pretty conductive. Thanks in advance if you have time to consider and respond! Cheers!
Hello can you do some video with outdoor antennas from 5Dbi to 12 dbi. For a Helium
What connector did you use to connect the main radiator to the so239 connector? I usually solder but I would like to be able to clamp it down like you did. I don't know the name of that device though. Thank you.
I used the metal part of the terminal strip block, see page 19 www.mobilefish.com/download/lora/lora_part42.pdf
Hi, can we use yagi antenna instead of using monopole antenna?
Yes, you can BUT watch out for the maximum allowed ERP in YOUR region.
In tutorial 39 is explained, when operating in the EU863-870 ISM band the maximum allowed ERP = 25 mW ≈ 14 dBm
To stay within the legal limit you must lower the end node transmission power when you use a Yagi-Uda antenna.
I will discuss the Yagi-Uda antenna in tutorial 48.
@@Mobilefish okay got it, thank you. Just can't wait for tutorial 48.
Ben jij ook de persoon die een HNT miner in A'dam heeft, die tot den-haag/rotterdam bereik heeft?
Ik heb geen Helium hotspot.
Please note, the way you compare the different antanna's is not correct. In order to get correct results you should tune the antenna's to the frequency you choose for the measurement.
Hi Raymond, do you mean for example that my monopole antenna was not correctly tuned at 868 MHz, and therefore I should not compare it with the tuned dipole antenna?
@@Mobilefish Yes, exactly. One can only correctly compare antenna's when they both are optimaly tuned to the same frequency .
Hi Raymond, you are absolutely right.
That is the point I am unsuccessfully trying to make.
Looking at your response I failed to get my point across.
Let me explain it better:
As you see in the video the ¼λ monopole without ground plane has a VSWR > 2 and I am ridiculously comparing it to a well tuned sleeve dipole antenna.
The reason why I am showing this comparison is to show you the effect.
But a ¼λ monopole without ground plane CANNOT be tuned to a VSWR < 2.
I have used the 4NEC2 program and used the optimised functionality and was not able to lower the VSWR smaller than 2 (you can try this yourself).
Unfortunately I did not explicitly mentioned this in the video (sorry, my bad).
Some LoRa device manufacturers include a wire (approx. ¼λ long) to be used as an antenna.
As demonstrated in this video a ¼λ monopole without ground plane has a bad performance.
If you use a ¼λ monopole with ground plane with R > ½λ than the monopole antenna has a good performance.
Dense