Antenna measurements with network analyzer. Help needed!

[manos87]

Hello to all,
I made two λ/4 monopole antennas with your precious help and now I need some guidance about the measurements.
First of all, I calibrated the network analyzer(HP 8714C) with the open, short and load and I tuned the antennas in order
to operate at 900 MHz. Also, I measured the reflection coefficient for the two antennas.
Due to the absense of a spectrum analyzer I thought to use a network analyzer in order to measure the received power.
Can you tell me how can I do that΄? Also, can I measure things such as delay spread with a Network Analyzer?
And, finally, what other important measurements can I do with the Network Analyzer, taking into account that the project
is focused on the wireless channel models(prediction, simulation and measurements).
Regards,
Manos

---------- Post added at 19:10 ---------- Previous post was at 17:55 ----------

Anyone?:smile:

 

[pstuckey]

Network analyzer is a standard way to do antenna tests. The network analyzer is both the signal source and receiver. Connect one antenna to port 1, the other to port 2. You'll want to do a transmission measurement S21. This will give the gain of both antennas plus the spreading loss between them. Typically one antenna will be fixed and the other will be moved. Also, note that if the antennas are far apart you may have to manually adjust (lengthen) the sweep time.

 

[manos87]

Thanks pstuckey!
The network analyzer that I use has the following options.
For port 1 has the option of A) Transmission and B) Reflection.
The same is true for port 2.
In order to get the S21 measurements I must set the port1 and port 2 to Transmission? or just port 2 to Transmission?
What is the right way to do it?
Also, the distance between the antennas will vary from 0,5 meter up to 20 meters. Why should I lengthen the sweep time?
Can you give an explanation?
I assume from your answer that we cant measure things like delay spreas with a network analyzer.
Regards,
Manos

 

[pstuckey]

What is the make and model of your network analyzer?

The network analyzer is probably not the best tool to measure delay spread since it is a tuned, swept receiver. This is also the reason that for long transmission distances you may need to adjust the sweep rate. If it is sweeping too fast it will have moved to the next frequency before it receives the energy from the prior one. This is usually only a problem for relatively large antenna separations (100's of feet), but if you see that you're not receiving any power, try to slow the sweep rate.

 

[manos87]

Pstuckey , thanks again.
I found a solution to the problem that I had. Also, about the delay spread it is not able to measure it, since you can measure only the phase difference between the reference signal and the recceived one, so you can measure only a time delay that corresponds up to 360 degrees phase shift.
From the S11 parameter, I get @ 900MHz -10dB which means that only 10% of the power is reflected.
How can I find the mismatch loss of the antenna and how this affects the Received power?

 

[pstuckey]

There are a variety of equivalent equations for mismatch loss,

ML = 10*log(1 - [(VSWR-1)/(VSWR+1)]^2)

Since you have two antennas in your system, you will have two mismatch losses.