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I'm using Atmel Atmega256rfr2 which is a 8bit microcontroller with a radio transceiver for IEEE 802.15.4 communication. They come in 2 evaluation boards #1 and #2. Both are almost same with the main difference being that #1 has an on-board debugger and #2 does not. Both the boards use on-chip ceramic antenna by default but also have the capability to use an external antenna. #1 has SMA female on board and #2 has MS 147 connector.

I want to use the external antenna and I'm not sure how to choose one. I have the following questions.

  1. Can I use any SMA male antenna for the 2.4Ghz range like this?
  2. For MS 147 on #2 should I use MS147 - SMA converter and then use SMA antenna? I cant seem to find a mating MS 147 male antenna.
  3. How do I select the gain and height? How much of a difference does it make to overall performance? One of the reasons I want to use external antenna is that the on-chip ceramic antenna does not fare very well outdoor. My hypothesis is that external antennas can provide better range and reliability.
  4. Can I use monopole or a dipole antenna?
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The connector needs matched to your entire setup. If your antenna is 50ohm then the connector needs to be 50ohm, the feed line needs to be 50ohm and there needs to be a converter that matches that 50ohm to your transmitter/receiver.

The antenna is going to depend on what range you need. The higher the gain the longer the range. That being said the higher the gain the more directional an antenna is. You have to analyze the antenna pattern to see what works for you.

The same advice goes for monopole vs dipole. As long as they are matched to your setup then only the gain and pattern will change.

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  • \$\begingroup\$ Thanks!. That makes sense. I understand the 50ohm part. How do I assess monopole vs dipole? There's no info on that by Atmel for that module. Also any input on the height of the antenna? Isn't the gain of the entire system limited by the max gain of the transceiver? \$\endgroup\$ – am3 Oct 27 '15 at 2:27
  • \$\begingroup\$ @AGM Your best bet is to use a dipole. A monopole requires extra design criteria especially ground plane considerations. The transmitted power is limited by the transceiver. The gain is how that power is shaped when compared to an isotropic antenna (an antenna that transmits its power in a perfect sphere). Imagine taking the sphere and squishing it into a doughnut. The height of the antenna will depend on the frequency of the signal. \$\endgroup\$ – vini_i Oct 27 '15 at 10:26

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