Yes I suggest you use SMA antennas regardless.
I also suggest to calculate the theoretical path loss and then validate your experimental data (ups my PhD just finished sorry!).
An example of calculation for a standard 2.4 Ghz Wifi router:
transmit power 125 mWatt = 21 dBm
receiver sensitivity -97 dBm
antenna gain 2.5 dBi
The attenuation is:
21 dBm – (-97 dBm) + 2.5 dBi + 2.5 dBi = 123 dB
(we add two antenna gain, because tx and rx)
In line-of-site conditions, every 6dB of link margin will double the transmission range. A radio with a link margin of 111
dB has 12 dB less link margin than the computed one, and thus it can only achieve a quarter of the range.
Then we have to consider the path loss:Link Margin
= Transmit Power – Receiver Sensitivity + Antenna Gain – Path Loss
Where the Free Space Loss is calculated with:
PathLoss= 20 Log_10(Mhz)+20 Log_10(distance)-147.55
In line-of-site conditions the path loss can be determined by using a mathematical formula (Friis transmission
equation). The path loss for a 2.4 GHz in free space is given for several distances in the table below.
Now let's assume that your antenna (like the one I have used for my Norduino) have a 3dBi, the nrf24l01+ has 1mWatt so is 0dBm.
The receiver sensitivity is:
-94dBm RX sensitivity a 250kbps
-82dBm RX sensitivity at 2Mbps
-85dBm RX sensitivity at 1Mbps
So the link margin is:Link Margin
= 0dBm – (-85dBm) + 3dBi + 3dBi = 91 dB
So the maximum distance that you can achieve at 91 dB is less than 30 meters.
This is what I measured in my test with Norduino outside on a street.
Of course then you have to consider multi path effects which will introduce further attenuation.
There are several studies about indoor RF propagation but then you go in the realm of simulations which is when you need some big computers.
I hope my computations will help you.
Keep my posted I'm really excited to sponsor your project.