Power measurements of RF power amplifier

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Mabrok

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I want to measure the output power of my designed power amplifier using spectrum analyzer. My device capability up to 40 dBm, but the spectrum analyzer limited to 30 dBm. So, what i can do in this case? Thank you
 

Hi,

the first thing comming to my mind would be the use of an additional external attenuator of at least 10 dB. You could test your amplifier up to an output power of 30 dBm without the attenuator and for a higher output power with the attenuator. If you haven't an appropriate attenuator you may built your own by means of a resistor network. To "calibrate" this attenuator you could perform the measurement up to 30 dBm output power a second time with the attenuator and compare it with your fist measurement series without attenuator.

In which frequency spectrum are you interested?

BR
 

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    Mabrok

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3.4-3.6 GHz (band of interset)
So, to measure 40 dBm output power with 10 dB attenuator I should consider that the output power displayed at the spectrum analyzer reduced by 10 dB. For example, if i got 30 dBm, means my actual output power 40 dBm (30 dBm + 10 dB of the attenuator), Am I right?
How if I used large attenuator more than 10 dB?
 
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Hi,

yes, if you use an attenuator with 10 dB your measured signal is attenuated by 10 dB, so your spectrum analyzer will show a magnitude reduced by 10 dB. You also can use an attenuator with a larger attenuation e.g, 20 dB which would decrease your measured signal by 20 dB. The important thing is to use an attenuator specified for your frequency band of interest e.g. up to 4 GHz.

BR
 

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    Mabrok

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Assign an Offset that is equivalent to attenuator value at your Spectrum Analyzer so you don't confuse.
 

So, for attenuator connection should be between the output of my device and the spectrum analyzer?
One more thing, do I need to use attenuator during small signal measurements (S-parameter) using VNA or the attenuator only for power measurements?
 

Hi,

Mabrok said:
So, for attenuator connection should be between the output of my device and the spectrum analyzer?
Click to expand...

yes, it is a passive two port device, and for your application you have to put it in series between your amplifier output and your spectrum analyzer input.

Mabrok said:
One more thing, do I need to use attenuator during small signal measurements (S-parameter) using VNA or the attenuator only for power measurements?
Click to expand...

As long you are not exeeding the maximum input power of your measurement device (VNA, spectrum analyzer) you do not need an attenuator. The maximum input power is usually stated in the vicinity of your measurement devices's RF ports. Note, you also have to set the internal attenuator of your VNA propperly to be able to use this maximum input power level.

BR
 

But in the case of s-parameter measurements, i just measure S11, S22,....etc. And there is no input power applied.
 

Hi,

of course also a power is applied for a S-Parameter measurements as each kind of voltage of your test signal represents a power at 50 \[\Omega\] (\[{P}_{out}\] = \[\frac{{V}_{out}^{2}}{50 ~\Omega }\]).
For example see the specifications of the ZVL network analyzer from Rhode & Schwarz [1]. On page 7 the adjustable output power is stated.

[1] https://assets.testequity.com/te1/Documents/pdf/ZVL_dat_sw_en.pdf

BR
 

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