antenna-theory.com

[masonlee]

Hi,

When we use spectrum analyzer to measure antenna receive power for gain calculation, i find out that the spectrum analyzer can measure few kind of powers like channel power, average power and total power. So which kind of power should i choose?

During the measurement with the spectrum analyzer, is it a must to see a peak in the receive power vs frequency plot? I found out that it still showing some power value even the screen does not show a peak.

How much the frequency span i should set?

Thanks

[wolberine]

What are you specifically trying to measure? Can you provide screen shots if possible?

[masonlee]

I trying to measure the radiation pattern and gain of an antenna. Just like the antenna measurement tutorial in this forum. I connect a spectrum analyzer to the antenna under test and measure the receive power.

When measuring the radiation pattern, at certain angle, the screen of the spectrum analyzer just showing a noise floor signal (without a peak) with low power level, can this low power be record? Is it accurate?

[bigSteve]

Antenna gain is a function of frequency. So the first thing to know is that when someone says the gain of an antenna is 3 dB, this means the gain at a certain frequency. The gain of a single antenna will generally be different at separate frequencies.

So the appropriate settings will depend on what you are using as an input. Remember that gain is basically the ratio of power received to power transmitted (factoring in the pathless). So if you want to measure the gain of an antenna at f=1 GHz, then typically you are sending a broad pulse of power and you want to know the energy at 1 GHz. So you may integrate over a frequency span around 1 GHz to get the power there.

Basically, you want the parameters you are using to determine the input power and output power (on your spectrum analyzer) to match. It doesn't matter exactly what you choose as long as you are consistent.

[masonlee]

From the data sheet of the spectrum analyzer, i found that it allow us to switch on/off a preamp. So what is the function of this preamp?