How can choose a good antenna


(Pierrot10) #1

Good day,

I need to order severals antennas, and I worries about the performance of the antenna. So, I have a couple of question.

More the antenna is big more the range will high? (I mean; more my node could be far from my gateway?)
Which are the criteria which make a high quality antenna, the size, the imedence, dB?

Here are the 3 antennas, I already have
http://shop.imst.de/wireless-modules/accessories/19/sma-antenna-for-ic880a-spi-wsa01-im880b-and-lite-gateway
I would like to buy some but from a shop in my country and I can find that antenna and antenna with the mention of LoRa. I wander, if I can simply order a GSM antenna or use some I already have. Is the LoRa antenna are different the GSM antenna.

Here are some idea I have:
Does a roof antenna is recommanded as this one
https://www.distrelec.ch/fr/antenne-gsm-aimant-fme-jiashan-jinchang-jcg016-fme-5m-ma/p/17840175?q=antenne&page=15&origPos=13&origPageSize=50&simi=95.49

https://www.distrelec.ch/fr/antenne-gsm-support-adhesif-fme-smarteq-710328/p/30062245?q=antenne&page=7&origPos=3&origPageSize=50&simi=95.49

Do the following are more recommandate (dB is higher)
https://www.distrelec.ch/fr/antenne-externe-ghz-microchip-trf1002/p/30056096?q=antenne&page=1&origPos=4&origPageSize=50&simi=96.49

https://www.distrelec.ch/fr/antenne-omnidirectionnelle-interieur-db-tp-link-tl-ant2408cl/p/11031423?q=antenne&page=2&origPos=39&origPageSize=50&simi=96.49

Many thank for your recommandation


(Tim Everitt) #2

Hi @pierrot10, because LoRaWAN operates in public/ISM radio spectrum the permitted power levels are very low, typically only +14dBm in Europe. This means that you will get better results from using an antenna that is very specifically tuned to operate in the ISM spectrum. In Europe the LoRaWAN profile operates in several channels close to 868MHz. So, before you look at the dBi gain, you should look at the Voltage Standing Wave Ratio (VSWR) for the antenna. This should be as close as possible to 1 at 868MHz. If you select a wideband GSM-type antenna that covers e.g. 850-1000MHz then it will work but not very well. You should search online for ISM antenna or 868MHz antenna. The following is an image from a datasheet for an antenna tuned for 868MHz.


(Pierrot10) #3

Thank a lot for your reply.
By the way I found the following additional information:
https://www.thethingsnetwork.org/wiki/Hardware/Gateways/Antennas
and
https://www.coredump.ch/2017/04/30/lorawan-868mhz-antenna-test-part-2/


#4

You might want to add The BIG ANTENNA topic part 1


(LoRaTracker) #5

Also be aware of the Effective Radiated Power (ERP) limits for your location.

If the ERP limit in your area is 14dBm (25mW) and you set the LoRa transmitter to 14dBm and then use an antenna of 5dBi gain, you will exceeed the ERP limit.


(Pierrot10) #6

That a lot for your answer. I would like to add a couple of questions.

First I heard that LoRa is a limit of 2dB. I am surprised and I think it a wrong information as TTN propose higher antenna. Can 8dB works as well. Lately I planned to buy a GP901C antenna. (5-8Db). I supposed, if my gateway has a such antenna, I could be farer with my nodes… That’s right?
(I understood, I have to be carefull with ERP and VSWR)

For now I will not buy a new antenna for my test of this week-end, For one of my node, I am going to use a 8cm wire, as an antenna. I would like to test until which distance a gateway can receive message from the node.

Then I am worried about a wired antenna as it’s shown in that picture
https://cdn-learn.adafruit.com/assets/assets/000/032/895/medium640/feather_3178_iso_demo_ORIG.jpg?1465414039

Can have the same result than with this 2dB antenna?
http://shop.imst.de/wireless-modules/accessories/19/sma-antenna-for-ic880a-spi-wsa01-im880b-and-lite-gateway?number=404811

Personnely, I do not think the wired antenna will be good as a normal antenna, but I just would like to ask you point of view, as I oft read somethink like this:"… you can as well use a wired antenna… if you do not have an antenna"

Will be the different largely different?

Thank a lot and have a nice day


#7

@pierrot10, don’t be mistaken about the wire antenna: it can easily outperform many other available antenna’s for your mobile devices if you need some kind of omnidirectional behaviour and if you have a bit of ground plane!
It is in fact a normal antenna: a quarter wavelength monopole. And it can be constructed very cheap from a piece of wire of about 8 cm’s.
If you only have a small piece of ground plane (relative to the wavelength), I think 2 dBi gain is typical for this type of antenna, and if you have a large groundplane (multiple wavelengths), 5dBi is about the theoretical maximum.

A lot of other smaller 868 MHz antenna’s are more or less derived from the quarter wavelength monopole by ‘folding’ it up; their performance is always inferior to the quarter wavelength antenna standing straight up