One A5c AP, (2) sector antennas possibility


#1

I am new to the technology, I wonder if you can have A5c radio and split the signal in (2) 65 degree sector antennas to make 120 degree radius? Will each of those sector antennas have H/V polarization combination?What antennas do you recommend?


#2

Hi Claudia,

It is possible to point antennas in different directions such that their patterns do not overlap, but you lose out on 6 dB of gain in doing so. Normally, twice the energy (3 dB) would be sent in the same direction, and beamforming would give an extra 3 dB for a total of 6 dB.

Another disadvantage would be that the noise floor would be inclusive of interference from two directions rather than one.

If you decide this is acceptable for your design, connect ports 1 and 2 to one antenna, and ports 3 and 4 to the other antenna. This ensures that each antenna receives inputs from each polarization.

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#3

Thanks a lot Chris :slightly_smiling_face:


#4

Hi Chris,

Can I clear up a bit of confusion I have on this scenario.

I’m a little fuzzy on how multiple chains play with EIRP limits. Assuming both antennas overlap (beamforming config), and assuming a 30dBm EIRP, does that mean antenna 1 can push out 30dBm and antenna 2 also can transmit 30dBm giving a total of 33dBm output therefore allowing us to get +3dB TX over the EIRP?

Also, do the antennas need to have some spacial diversity to get the +3dB on RX?

Regarding the interference I had assumed (possibly incorrectly) that interference heard by antenna 2 would not affect a good signal received by antenna 1? ie, each antenna had their own “noise domain” so to speak. If I understand what you say above, there’s no significant difference having 2 x dual chain 30* sectors versus 1 x dual chain 60* sector?

Thanks,
Richard


#5

Hi Richard,

Since the two antenna gains are likely higher than 0 dBi, Tx power must be set to a level that does not exceed the mentioned 30 dBm EIRP, but I’ll use 30 dBm as the transmit power in the following theoretical example to keep things simple.

Assuming that an A5c is set to its maximum transmit power of 30 dBm, that power would be divided among the four chains resulting in 24 dBm per chain. Combining two chains on one antenna would result in 27 dBm of Tx power per antenna. If the two antenna patterns overlap (pointing in the same direction), then the combined power is 30 dBm in that direction. If the two antenna patterns do not overlap (pointing in different directions), then only 27 dBm of power is sent in either direction.

The extra 3 dB of beamforming gain comes from amplitude and phase shifts at the transmitter such that the signals add constructively at the receiver, so this effect does not count against EIRP. Beamforming requires that the antenna patterns overlap in the direction of the receiver so that it receives both signal components. No spatial diversity is required at the transmit antenna. In fact, 4x4 antennas contain four antenna arrays in one package, all facing in the same direction.

Both signals and noise are additive among the four chains (one radio). They do not have separate “noise domains”.

There is a 3 dBm transmit power difference between two 30° 2x2 sectors and one 60° 4x4 sector. The difference is because two 30° sectors do not overlap when covering 60°, while a 60° sector contains four overlapping patterns. Since non-overlapping patterns cannot be used for beamforming, the net result is a -6 dB gain difference.