4G LTE device: 1 or 2 cellular antennas?

[Martin F]

Hi all,

We're developing a data logger with a 4G LTE Cat 4 module inside (e.g. EG25-G or LARA-R6).

As part of this, we're considering whether we will need 1 or 2 cellular antennas. Our understanding is that 2 antennas enable faster download speeds and e.g. utilization of MIMO functionality. However, for our user case we will 99% be focused on upload speed (with download only being periodically relevant for small OTA updates of a few kb). Hence we're wondering if there are any practical downsides to using 1 antenna for the upload/coverage performance?

Thanks!

[E Kafeman]

If weak Rx signal can MiSo using two antennas improve communications stability, faster channel setup, which indirect improves upload and can reduce number of ARQ.Improvement is probably in most cases marginal so guess reduced antenna space and cost is of higher value.
If you implement an u.fl connector for second antenna can that antenna be added only at weak signal locations.Keep decent antenna isolation between the both antennas or else can 2:nd Rx antenna reduce Tx and Rx efficiency for 1:st antenna by unwanted coupling/loading. Antenna isolation is in any case needed for improved Rx coverage.

[thm_w]

One antenna is fine.

Its going to be more about the quality of that antenna than if you have one or two.

[E Kafeman]

Have a bit hard to understand what you base your opinion on with "one antenna is fine" in a MiSo system with two active receivers.
Can you explain what "fine" is?
In a functional Cat4 MiSo system is maybe one antenna good enough if somewhat reduced performance is acceptable for both Rx and Tx.

As example: a poor Rx function due to local noisy environment affects possibilities to establish a Tx communication channel even if Tx coverage is good enough. Two antennas relative a single antenna will always improve data rate and BER in a such environment.
In a more ideal noiseless environment is Rx coverage improved with 50% if using two antennas, which is of gain to keep a stable upload channel under else too weak signal conditions.Can you also explain what you want to say with "Its going to be more about the quality".
Is it a measurable antenna parameter such as antenna efficiency, bandwidth or size that differ for one relative two antennas?
 
If a single antenna is top performing can it still never outperform two similar antennas in a functional MiSo system.
It is more a factor of non antenna performance parameters which can make a single antenna preferable over two antennas, such as antenna cost or space savings.

[SmallCog]

As an end user of dataloggers I can perhaps give you some user perspective

If it's a small thing I'm trying to stash inside a cover or covertly install outside the last thing I want is 2 antennas to try and deal with. No big deal if they're internal but if they're external it's a headache I don't need.

If it's more "heavy duty" ie designed for long term environmental telemetry, there'll probably only be one omni or yagi on the mast to hook it to. Hydro's aren't RF experts and struggle with the concept of mounting one antenna correctly, give them 2 and they're guaranteed to stuff it up or just not connect one of them.

Final bit of perspective, if it's an all in one unit it needs to be cheap, we have some loggers deployed that are on their 3rd modem technology with the shutdown of 2G services, then 3G services they've now got a 4G serial modem attached. The same loggers could just as easily also have satellite or radio links attached and are infinitely useful

I also have an E waste bin full of all-in-one loggers that have built in 3G modems and will soon be useless. Great loggers that still work perfectly but no good if they can't dial home... If I'm buying something with a built in modem I take its shorter lifespan into account when considering it's price.

[Martin F]

Thanks a lot - great inputs!

[thm_w]

Have a bit hard to understand what you base your opinion on with "one antenna is fine" in a MiSo system with two active receivers.
Can you explain what "fine" is?
In a functional Cat4 MiSo system is maybe one antenna good enough if somewhat reduced performance is acceptable for both Rx and Tx.

As example: a poor Rx function due to local noisy environment affects possibilities to establish a Tx communication channel even if Tx coverage is good enough. Two antennas relative a single antenna will always improve data rate and BER in a such environment.
In a more ideal noiseless environment is Rx coverage improved with 50% if using two antennas, which is of gain to keep a stable upload channel under else too weak signal conditions.Can you also explain what you want to say with "Its going to be more about the quality".
Is it a measurable antenna parameter such as antenna efficiency, bandwidth or size that differ for one relative two antennas?
 
If a single antenna is top performing can it still never outperform two similar antennas in a functional MiSo system.
It is more a factor of non antenna performance parameters which can make a single antenna preferable over two antennas, such as antenna cost or space savings.

Its a datalogger, if you are in an environment with good signal strength, it will likely not matter. OP has not specified.

But yes you are correct, MIMO/MISO will outperform SISO so the question is if the cost and larger antenna size taken is worth it.


https://www.scirp.org/html/1214.html
https://cdn2.hubspot.net/hub/246745/file-437490900-pdf/M2M_Cellular_Antennas_SISO_v_MIMO.pdf