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I want my n/ac Wi-Fi card to operate in a spatially directional manner. To achieve that I want to use a directional antenna(s). There is a slight complication though, because my Alfa AWUS036ACH network card has two omni-directional antennas.

Because of that, I'm confused on how I should connect a directional antenna to such a setup. I can imagine a few options, but I don't have the experience to judge what would give me the optimal gain in dBm.

I can see the following options:

  1. Connecting two directional antennas and pointing them in one direction. The problem here is that the antenna connectors are very close to each other and two directional antenna would not fit that close together. So, I would have to extend connector using cables and build some frame to hold the antennas. A lot of work, and cables incure signal loss.

  2. Disconnecting one omni and connecting one directional. Problem here is that I don't know if the NIC can work using one antenna.

  3. Connecting multipatch antenna -- quite expensive, but if that is the only option then I have to go with that.

Or maybe some other option?

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  • $\begingroup$ Welcome to this site! I have slightly clarified your question in hopes that it will help you to get multiple good answers to your very interesting (to me) question. I hope that you don't mind. :-) $\endgroup$ – Mike Waters Apr 12 at 18:33
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Wireless NICs and APs have multiple antennas for MIMO. This means the device dynamically determines the coefficients for each antenna to combine them in the best way.

Often that means phasing the antennas to make an array with greater gain towards the other station and/or less gain towards interference sources. This is called beamforming. So your NIC is already "spatially directional" in a way. A device with more antennas could be even more directional.

Additionally, the device can find two sets of orthogonal coefficients and use this to double the data rate. This is called spatial multiplexing.

One solution to your issues may be to simply upgrade the NIC. Higher end devices may have 4 or even more antennas, and with more antennas in the array comes the potential for a more directional array. NICs are cheap enough this may be cheaper than buying antennas.

Alternately, attaching two directional antennas would work well. This allows the NIC to still gains the benefits of MIMO, while adding gain in the direction where you need it the most. Unless the cables are going to be very long, it's likely the cable loss will be more than offset by the additional gain.

Even if you attach just one directional antenna and leave the other omnidirectional antenna attached, the NIC will likely weight the directional antenna more heavily. Though this does mean you are less likely to get the higher data rates associated with spatial multiplexing.

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Looking at this information about your 802.11ac USB antenna, those two antennas are not on the same frequency. One antenna is for 2.4 GHz, and the other for 5 GHz. Since they are independent of each other, this is not a phased array of two verticals.

Dual band WiFi antennas

If you only need one of those bands, I suggest that you only remove the one that you want the directional antenna attached to, and leave the other antenna alone.

Since they have RP-SMA female connectors, those antennas can be disconnected. But I'll leave the details of the antenna and feedline to others here that are experienced in these WiFi frequencies.

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    $\begingroup$ It also claims a top speed of 867 Mbit/s, which requires 2 streams. So I suspect this image is misleading, and it really is a MIMO device using both antennas. $\endgroup$ – Phil Frost - W8II Apr 12 at 19:23
  • $\begingroup$ @PhilFrost-W8II Oops! Thank you. Sounds like it's not so simple, huh? $\endgroup$ – Mike Waters Apr 12 at 19:26
  • $\begingroup$ I guess that I should eventually delete this answer, but @PhilFrost-W8II 's comments are useful. (As is the case in his answer!) $\endgroup$ – Mike Waters Apr 12 at 19:29
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    $\begingroup$ I lied...looks like 802.11 ac can do 867 Mbit/s with a 160 MHz channel and 1 stream. But it also claims 300 Mbit/s on 802.11n, which requires 2 streams with a 40 MHz channel, and I don't think 802.11n has any provision for wider channels. $\endgroup$ – Phil Frost - W8II Apr 12 at 20:35
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    $\begingroup$ I suspect it will work with just one antenna, but you won't get MIMO speeds or any of the benefits of antenna diversity. $\endgroup$ – Phil Frost - W8II Apr 12 at 21:06

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