Active Antenna IP3 measurement

[fussylogia]

Hi,
I have an active HF antenna with the spec of IP3>30 dBm. I have to verify this spec. However, when i establish my setup and try it, it dose not give IP3 close to 30. Then i removed antenna system and worked only with 2 signal generators, a power divider and spectrum analyzer.Even then i can only get 26 dbm IP3.
-Does power divider create harmonics?
-Does signal generator or spectrum analyzer create harmonics?
-Is there any method, to measure IP3 of an active antenna?

Thank you for your considerations.

 

[VSWR]

- Check isolation between signal generators. You may have to insert an extra 10 or 20 dB attenuator between each signal generator output and the power splitter, to prevent intermodulation between the signal generators.

- Check the spectrum analyzer linearity. Increase the spectrum analyzer input attenuator by 10 dB. The intermodulation level shall then also drop exactly 10 dB. If not, the input signal level to the spectrumanalyzer is too high and will cause intermodulation in the spectrum analyzer itself.

 

[normaldist]

The divider should not cause any intermod, but you should add attenuators at the out puts of each sig gen, you can't count on the divider having enough isolation.

If the attenuation on the spectrum analyzer gets you input signal to the linear range, you will be able to accurately measure the intermod.

 

[purushottam]

Can you please give the setup that you have used, fussylogia?what was the result for ip3 with the active antenna system?

 

[Mazz]

Let me add that, being the IP3 a non-linearity measure to be performed in "linear" conditions, the input power level have to be well below compression of amplifier (rule of thumb is -20 to -10 dB below P1dB).
Check also that you have the 3dB/dB slope of intermodulations (increase input power by 1 dB, see 3 dB more in intermod products).
Furthermore: check that both signals and intermods are in amplifier flat band (and if you have a filter in your antenna, it can be the case).

I hope it can help.
Mazz

 

[AswinSJ]

Sorry for the little diversion from the main topic, I have two questions that I would like to ask while we are still in IP3 measurement topic.
1. What role does the IP3 of the measurement setup plays in the actual IP3 measurement?
For instance: If I want to measure a DUT with 30dBm O/P IP3, will a setup with an IP3 of less than 30dBm work? If not how high should it be?
2. Is there any other way of determining IP3 for attenuators(PIN diode) other than the conventional two tone measurement?
I ask this because lets say my attenuation is 40dB and my OIP3 is >30dBm, my SNR is going to be pretty low to get reliable measurements.

 

[Mad2Max]

In attachment the measure setup you can use ...
Regards,
Max

 

[fussylogia]

My system did not respond with full qualifications. I am beginning to thing this is much of a DUT failure other than mesurement setup. I tried anything i can. Thank you for your considerations.