Starting with S1.2 VNA and smith charts

[alaios]

Hi all,
I am training myself with antenna design (I am very new to this field) and I would like to train with VNA and S1.2 , S2.1 measurements.
I got a test board from a friend that has two antennas that end up to two sma jackets (so connecting to a VNA) will not be a problem.

I would like
a. To read more on S1.2 measurements with VNAs (including calibration). Do you have any good resources for that (I am googling it but I can find pieces here and there)
b. How to work with a VNA and smith charts to match both antennas. The idea is not just to get the smith chart but also to understand on what type of components I should need to add to make all the energy real. That means that I might also need to refresh my knowledge in matching (in the board I have there is space for matching components).

Thanks for your help and suupport.
Regards
Alex

 

[BigBoss]

Using VNA in antenna measurements is a piece of process.Antennas are essentially measured in Faraday Chambers with a reference antenna and all characteristics ( directivity,gain,side lobes etc.) are essentially measured in those chambers.VNA can only measure the Input Impedance of an antenna but chamber is a must for serious measurements.

 

[FvM]

VNA can only measure the Input Impedance of an antenna

The instrument can also measure s21 (or s12) of a two antenna transmission path in an anechoic camber (or on a meadow, if it makes sense for you).

 

[alaios]

The instrument can also measure s21 (or s12) of a two antenna transmission path in an anechoic camber (or on a meadow, if it makes sense for you).

Yes actually I would like to measure how much power from antenna one "leaks" to antenna two and the vice - versa.
I have VNA but you are right I should position my VNA and the board I have inside a chamber to eliminated effects of the environment.

Regards
Alex

 

[FvM]

I'm not quite sure what's meaned with "match both antennas" in post #1.

You'll usually match antenna to a transmitter or receiver impedance to achieve maximum power transfer. Smith chart is a good tool to design the matching network. VNA is used to measure antenna and transmitter/receiver impedance and to verify the matching. The measurements are involving different problems, antenna impedance measurement can be disturbed by environment and cable effect. Receiver and transmitter are non-linear devices any possibly not suitable for VNA measurements. Other methods like load pulling may be preferred.

 

[BigBoss]

The instrument can also measure s21 (or s12) of a two antenna transmission path in an anechoic camber (or on a meadow, if it makes sense for you).

Using VNA is impractical in antenna measurements due to measurement cable length,Instead I prefer an reference Antenna and a Power Meter/Spectrum Analyzer.
The distance between reference and receiving antenna may be around 5m or more depending on the frequency.

 

[alaios]

I'm not quite sure what's meaned with "match both antennas" in post #1.

You'll usually match antenna to a transmitter or receiver impedance to achieve maximum power transfer. Smith chart is a good tool to design the matching network. VNA is used to measure antenna and transmitter/receiver impedance and to verify the matching. The measurements are involving different problems, antenna impedance measurement can be disturbed by environment and cable effect. Receiver and transmitter are non-linear devices any possibly not suitable for VNA measurements. Other methods like load pulling may be preferred.

Thanks for the reply. Indeed I have written my post in a way that is a bit confusing. My apologies for that. My experience with antennas is CST simulations and the books that I read so I lack a lot in hands on experience.
In CST for example when you have two antennas on the same board you try to match them so you move frequency (antennas are being detuned when they come close to other antennas) but also increase power being transferred to antenna. As you match the one antenna you detune many times the second one and thus the simulator works on finding the tradeoff.

Now if I want to try to do this matching (improve power transmitted to antenna) and move frequency to the band of interest, I would think that the next step will be to use a VNA and smith charts. I miss a bit on the understanding on how to use VNA to do: impedance matching, antenna tuning.

Does this information help a bit more? If yes, are there articles on using VNA for antenna related work? Thanks a lot