RF Power Amplifier Measurement

[LaughingMAN]

I'm confused about the 50ohm load in the RF Power Amplifier. My questions are:

1. In simulation, I usually put in the 50ohm load, but when you do the actual design, do you omit out the load and replace it with an external load to do measurement? What would happen if you don't put in the load?

2. Most instruments such as PNA says that it is terminated with a 50ohm load, does that mean that I don’t need a external load when doing s parameter measurement?

3. I have seen most people using attenuator at the output of Power Amplifier to do measurements, is the attenuator similar to a 50ohm load but with power attenuation?

4. The RF power meter has a power sensor, which can dissipate power, so do I need an external load as well?

Any help would be much appreciated.

 

[G4BCH]

1. In simulation, I usually put in the 50ohm load, but when you do the actual design, do you omit out the load and replace it with an external load to do measurement?
Yes. The load is where the power is going to be dissipated, commonly an antenna.

What would happen if you don't put in the load?
Depends on the amount of power you are generating and the ability of the output device to withstand mismatched loads. Generally a bad idea you could easily destroy the output device(s) and or other components in the output stage.

2. Most instruments such as PNA says that it is terminated with a 50ohm load, does that mean that I don’t need a external load when doing s parameter measurement?
Only for low power. Test equipment loads are generally only rated for a few milliwatts. Use an attenuator or external couplers and loads that can handle the power. The test equipment manufacturers usually have application notes on how to do this with their particular instruments.

3. I have seen most people using attenuator at the output of Power Amplifier to do measurements, is the attenuator similar to a 50ohm load but with power attenuation?
Yes if the attenuation is high enough. They are usually PI pads.

4. The RF power meter has a power sensor, which can dissipate power, so do I need an external load as well?

Not for low power. Most power sensors are rated for 10 to 100mW, some are much lower. They are very easily destroyed. Always use an attenuator to get the power down to a level that can be safely handled by the sensor.

Peter

 

[ananth]

Hey..
Informative stuff.. G4BCH..
thanks