Antenna Received Power measurement using VNA

[Nia11]

Hi,

I need to measure the received power of the wifi antenna using vna.
VNA used- M9370A keysight.
Receiver antenna specifications– omni directional whip antenna
• 2.4-2.5GHz
• 2.15dBi gain
I connected port 2 of vna with the receiver antenna while the port 1 is connected to the 50 ohm load.
I have to measure the amount of power received by the antenna that is connected to the vna.
I don’t know much details about the transmitter, The only thing I know is that the transmitter is a wifi patch antenna
In the vna, I choose the dBm power option instead of s parameter to measure the power received by the receiver antenna. I have attached the figures of the vna window screen along with the post.


Since I connected my receiver to port 2, I selected Meas -> Receivers -> Activate-> B, you could see that in the attached figure 2.





The resulting figure shows the received power in dBm, which is -27.15dBm @ 2.4 GHz.
The problem is when I convert the power in dBm (-27.15dBm) to watts, I get very small power value that is equal to 0.00192 mw or 1.92 µw.
Is the measurement procedure is wrong? Or this the actual power received?

(p.s- I didn’t do the measurements in anechoic chamber), Thank you in advance.

 

[D.A.(Tony)Stewart]

Normally you measure S11 by transmitting to antenna under test and monitor using directional coupler with known S12 loss by calibration.
then calculate Friss Loss vs distance and compare with known whip antenna gain. Ground planes affect gain and echoes off walls and nearby objects affect S11 which should be >-15dB.

Then reverse antenna and repeat.

Or use splitter to measure S21 between port 1& 2 and then insert antennae.

 

[Nia11]

Normally you measure S11 by transmitting to antenna under test and monitor using directional coupler with known S12 loss by calibration?.

Hi, Thank you for your post.
I have attached the block diagram of what you have asked me to do in order to measure the power.

Is this block diagram is right?

Friis transmission equation:
Pr= Pt+Gr+Gt+20log(λ/4πR)

So, by using directional coupler, I have to measure S11 and substitute S11 as Gr in the above equation.
And then I have to substitute the actual whip antenna gain as Gr in the friis equation and then to compare both the calculated equation.
But the problem is as I said earlier, I don’t know the power transmitted by the transmitter (Pt).
So what is the solution for it?

 

[FvM]

I don't understand the purpose of thís setup. S11 can be measured by a VNA as single port measurement directly, using the internal directional coupler.

 

[mtwieg]

A VNA measures network parameters, including the power gain between ports, but isn't the appropriate instrument for measuring absolute power. A spectrum analayzer/signal analyzer is the proper instrument for that. Using a VNA to measure the S parameters of a transmitter/receiver could allow you to calculate the received power, if you know the transmitted power a priori.

I don't know what the "dBm" option in your VNA means, but I don't think it's equivalent to a SA.

 

[Nia11]

Using a VNA to measure the S parameters of a transmitter/receiver could allow you to calculate the received power, if you know the transmitted power a priori.

Hi,

how could I calculate received power with the help of s parameters?