Electronics > RF, Microwave, Ham Radio

RF Attenuator and connector behavior after exceeding frequency rating.

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robert1111:
Hello.  What is the result when the applied frequency greatly exceeds the frequency rating of a RF attenuator?  For example, applying a swept signal from 3GHz to 40GHz for a 3GHz rated N type coaxial attenuator?  How about for a 18Ghz rated coaxial SMA attenuator?  What happens when a swept signal from 3GHz to 40GHz is applied to a N type connector that is only rated for 11Ghz or 18Ghz?  What is the physical difference between the 11Ghz and 18Ghz N type connector?  What happens when a swept signal from 3GHz to 40GHz is applied to a SMA connector?  Thank you for your help.

xmo:
There are no 40 GHz 'N' connectors.  Exceeding the connector's rated frequency can introduce “modes” in the frequency response. A “mode” occurs when the connector structure becomes a weakly resonant cavity. This resonance would appear as a very narrow band “suckout” in the connector insertion loss.

robert1111:

--- Quote from: xmo on June 16, 2021, 11:16:22 pm ---There are no 40 GHz 'N' connectors.  Exceeding the connector's rated frequency can introduce “modes” in the frequency response. A “mode” occurs when the connector structure becomes a weakly resonant cavity. This resonance would appear as a very narrow band “suckout” in the connector insertion loss.

--- End quote ---

Does this mean the attenuation can be greatly reduced in the mode frequency?  By "suckout" do you mean increase or decrease in insertion loss value?

TheSteve:
Often bad things happen. You can exceed the frequency of the connector itself, you may experience moding as a result. The bigger issue is that attenuators often perform very poorly beyond the specified frequency.

Let's take a look at a Mini Circuits 10 dB SMA attenuator from 300 kHz to 26.5 GHz. This is part # VAT10+, with a rated frequency of 6 GHz
You can see it performs just fine to 6 GHz. Beyond that all parameters are less then ideal.

TheMG:
With connectors, the result would usually be an increase in insertion loss at certain frequencies worst than others. It won't be a nice gradual increase as you go up in frequency, there will be all sorts of dips and bumps.

As for RF attenuators, these can go both ways, the attenuation value may go both above and below the attenuator's spec.

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