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I am working on a ultra low power project where portability and low weight is important. The circuit would have multiple ICs, that need to communicate over multiple frequencies:

  1. Esp32 - WiFi/Bt 2.4 Ghz
  2. Sx1262 - LoRa 868 Mhz
  3. Neo6Mv2 - Gps 1.5 Ghz

I found multiband chip antennas that cover all of these frequencies, e.g: https://ignion.io/product/run-mxtend/

  1. The question is that can this be used as a common, shared antenna for all the ICs?
  2. Can they use it simultaneously or it has to be time shared?
  3. What are the pros and cons of sharing the antenna?
  4. Any supporting circuit is needed?
  5. Is there any learning material, similar project that can be looked at for inspiration?

Thanks

Márton Kéri
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  • If simultaneous use of the antenna by multiple IC is not required you should try to use a RF switch. in the hypothesis the ESP32 manage all the transmission, it could also manage the switch to connect the right IC to the antenna at the right time. – Wireless Learning Aug 26 '22 at 11:08

2 Answers2

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Actually, it can be done, but the extra cost, size and weight may be prohibitive. What you're asking for is a three-band RF power combiner/splitter. If you google for these, you will find various devices; most of them are large and expensive but you could have a look at this one which comes closest to your requirement: https://lora-developers.semtech.com/uploads/documents/files/An_Evaluation_of_Multi-band_Antennas_for_use_with_LoRa_Edge%E2%84%A2_Part_One_v2.0.pdf In particular this drawing: enter image description here

Paul
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  1. The question is that can this be used as a common, shared antenna for all the ICs?

If the manufacturer claims it is wide enough for that, all RF traces are 50 ohm and a suitable RF switch is used, then sure.... But I doubt it will be an ideal antenna for either technology.

  1. Can they use it simultaneously or it has to be time shared?

It can obviously not be used simultaneously, sending two different RF signals to the same antenna at once will create a complete nightmare of all manner of complex RF problems.

  1. What are the pros and cons of sharing the antenna?

Pros: No need to consider multiple antenna placements and how they affect and interact with each other, if they would otherwise need to be mounted in close proximity to each other.

Cons: complex software, complex product, forced to use unnecessarily wide and specialized antennas, forced to adapt hardware filters per radio band in "run-time", very complex EMC testing, very complex and expensive product compliance testing - any pre-compliance to Bluetooth/Wifi etc product standards has to be done all over again. We are talking about several 10k€ added in testing costs.

  1. Any supporting circuit is needed?

I think it would only be feasible to do this using some manner of Software-Defined Radio computer. They are relatively big and expensive, plus you need to learn how to program them.

  1. Is there any learning material, similar project that can be looked at for inspiration?

No idea, all of this sounds like a very bad idea to me.

Lundin
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    "It can obviously not be used simultaneously, sending two different RF signals to the same antenna at once will create a complete nightmare of all manner of complex RF problems." Not necessarily. Antennas receive multiple signals at different frequencies all the time with no issue in the antenna itself (problems occur in the amplifiers behind the antenna if they go into compression). Since most antennas are reciprocal, they can also handle multiple simultaneous transmit frequencies at the same time. – SteveSh Aug 26 '22 at 11:45
  • @SteveSh But how would prevent one tx path from sending energy into the other tx paths? How would you prevent intermodulation? – Lundin Aug 26 '22 at 11:57
  • But that's more a question of how the PA (power amplifier) behaves, not the antenna. I wasn't saying you might not have issues - just that any such issues are not caused by the antenna itself. – SteveSh Aug 26 '22 at 12:22
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    @Lundin diplexing. And intermodulation only happens at nonlinear elemements, of which an antenna (at low power levels) should be none. – Marcus Müller Aug 26 '22 at 13:25