About anternna test question?

[luckyql]

Hi,guyes,
How to set up the ventor network analyzer ?when i want to test a GSM anternna? if the VNA is total frenquency span is 0 to 8GHZ,but i want to test anternna the vswr @1800MHz ,how to set the frenquency span? thanks a lot!

 

[venu.gongal]

U need to know whats the range of frequencies it operates ( bandwidth of the antenna) .For a GSM 1800, 1710–1785 Mhz for uplink, 1805–1880Mhz for downlink.

 

[Kohi_boy]

What are the parameter of the antenna you are interested to know? Radiation or impedance?

 

[luckyql]

I want to test the anternna's reflection perforance --vswr.

---------- Post added at 04:41 ---------- Previous post was at 04:28 ----------

Hi,venu.gongal:
I want to test the DCS1800 band of the anternna @1810MHz,(test vswr).but I found that have difference vswr value when I set up different frenquency span:1. 1GHz--2GHz;2. 1GHz--3GHz; 3. 1.5GHz--2GHz; 4. 1.5GHz--3GHz. Why have a contrast ?which frenquency set is better to measure precision?Thanks for you give explanation!

 

[sv1437]

There should not be any difference in VSWR value for different frequency spans. I know the reason why you are having different VSWR values. The reason is when you change the frequency span,you need to RECALIBRATE the network analyzer.
You get correct values only for the frequency range that you calibrated, once you change the frequency range you will get an error message on the screen of the VNA that your calibration is not set.

If the VNA is calibrated for every frequency span that you are planning to measure, you will get the same VSWR.

 

[luckyql]

but i calibrated the VNA from 300KHZ to 8GHz.

 

[Kohi_boy]

1) How much difference? from VSWR 1.5 to 3? or 1.5 to 1.6?
2) Did you test it in a proper environment? No significant reflection or noise source?
3) Thermal noise (KTB) is a function of bandwidth. The large calibration range of yours might have raised the noise level.

 

[sv1437]

Hi luckyql,
Even though you calibrated the VNA from 300 KHz to 8 GHz, you need to recalibrate the VNA if you change the frequency span.
Why don't you do a simple measurement, measure the VSWR at the frequency range from 1 GHz to 2 GHz and again measure the VSWR from 1GHz to 3 GHz (after recalibration). See whether they are equal or not.

-sv