Attenuator and Isolator for RF power amplifier power measurements

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Mabrok

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Hi,

Please I need help with the following:

I'm doing high power PA of about 43 dBm (about 20 watt). I will use a driver stage In front of the final stage, and will have to use isolator between both stages. My question how to choose the suitable isolator? Frequency? power? and Isolation?

Secondly, I have attenuator with 40 dBm attenuation and wider bandwidth. But, it is power capability is 2 watt. So, can be used in my design as the power out of my design is high (about 20 watt). Please advise me? Thanks in advanced
 

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In PA design generally isolators are used at the output of the final stage, and rarely between stages. Between stages an attenuator should be enough.
Choosing an isolator, all 3 characteristics are important: frequency, power and isolation.
If use a 2W attenuator at 20W, it will burn in few seconds (maybe less).
 

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-Isolators are used to protect the PA against Mismatch between PA and Load. It should have a specification for the right power and right frequency. If we assume your PA has 15dB Power Gain, the Output Power of the Driver Amplifier will not exceed 28dBm ( more or less ) so 0.623W is not a dangerous value for Mismatch.
-For attenuator, the power handling capability is selected regarding to attenuation value. For instance if you would measure the PA with a Spectrum Analyzer that has a typical Input Power 20dBm, the Attenuator must have 23dB attenuation value and at least 25 W power handling capability in your case because most of the power is dissipated at the attenuator.
 

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    Mabrok

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Thanks for the valuable information.

Output power of my driver amplifier is about 38 dBm and the target frequency is 3.4-3.6 GHz. So, how much should be the power, frequency, and isolation of the isolator?

For attenuator, how much should be the frequency range for PA designed at 3.4-3.6 GHz?
 

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You have to search the Isolator on Internet, I don't know a model number by heart. But I have explained as before, The Power Handling Capability must have at least Output Power of the PA.
-Attenuators are generally very wideband because of their resistive structures so it doesn't matter the frequency band for a professional grade attenuator.
SunnySkyguy said:
To protect your design from mismatch reverse power > 38dBm https://www.uiy.com/Datasheet/UIYBDI2528A.pdf
Click to expand...
Seems adequate. But there may be other brands and models.
 

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    Mabrok

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Mabrok said:
PA of about 43 dBm
Click to expand...

Mabrok said:
Output power of my driver amplifier is about 38 dBm
Click to expand...

What is your PA gain?
If you want some isolation between driver and PA, you might use an attenuator of 6dB or so, because your driver can handle quite large power and the PA will have more than 5dB gain.
 

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