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Power Amplifier protection against high VSWR?

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Advanced Member level 4
May 17, 2002
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How to protect power amplifier against high VSWR?

On which side do you want to protect the amplifiers against high VSWR? Input or output? What frequency?

Measure the reflected power that is directly related to VSWR. You need a very good directional coupler and a a good detector (you need to compensate it in temperature).

one way is to Use a circulor to Prevent refelcted signal

That way you are deliverying power to a not matched load (why it is unmatched?).

If during operation ANT cable is disconnected(OPEN) then the PA will be damaged,protection is a good thing for more reliable systems also.

do you use protection for PA at your design?

I mean protection at OUTPUT of PA.

No because of the wide band but transistors like LDMOS are very ruggedness and if you are very quick in detection and in switching off the driver you should succeed in protecting your amplifier

Normally there should be some mistmatch at the output. I mean, perfectly matched does not mean max output power.

Anyway, if you want be able to remove the antenna without damaging the PA a way is to measure the reflected wave with a coupler + ADC and turn off the PA.

Best regards,

How do you connect PA to antenna?
If you are using a waveguide, you may done it indirectly by measuring the air pressure in it. (if there is a great lost of pressure, the waveguide must be disconnected, or badly damaged). If pressure falls badly, use automatic device which will shut down PA.

If you are not using WG, circulator is best, but the most costly solution.

You also may try with ferrite insulators.

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