Electronics > RF, Microwave, Ham Radio

RF Attenuator and connector behavior after exceeding frequency rating.

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Thing to keep in mind is that you can sometimes operating things above the higher mode frequency. Just because they can exist, does not mean they will be excited, and if the propagation constants are sufficiently different very little energy will transition from the desired mode into the undesired mode, provided there are very little defects or other structures that can excite this mode.

This is how you get N-connectors going up to 26 GHz, and BNC connectors going up to like 10 GHz on some Keysight scopes.


--- Quote from: djidji on August 04, 2021, 02:16:57 am ---an very very good and very very very expencive N connector will have satisfactory characteristics up to the 21,5GHz, but if you need or require very low insertion loss and excellent return loss, than N connector is usable up to the 12GHz only. for higher frequencies you must use the SMA (up to the 26GHz or APC7 (up to the 18GHz) then K (good up to 40GHz) or APC3.5 (good up to 26GHz). for frequencies above 40GHz comes the RPC-1.85, RPC-1.35 and RPC-1.3 (110GHz) connectors.

--- End quote ---

There are "grades" of connectors: commercial, precision and metrology.    N connectors have a 7 mm outer conductor and so have the same limitations as APC7 in a precision version.  SMA is really only good to 18 or 20 GHz due the solid dielectric (teflon) and has a 3.5 mm outer conductor inner diameter.  The air dielectrice 3.5 mm connector is good past 26.5 and pretty usable up to mid 30's.   Commercial versions don't  have well defined transitions and so form kind-of low-pass filter structures (might have, for example, too wide of a center conductor causing excess low impedance like a shunt capacitor).   2.92 mm (K connector) is good to 40 or a bit more; 2.54 mm is common up to 50 GHz and is the Keysight standard.  then 1.85 to 67 (but works OK to 72 ish), then up to 1 mm for 110 or 120 GHz (depends on the bead).

For your attenuator question: it depends all on the design of the series and shunt resistors.  Keysight uses a thin-file "patch" resistor which is quite broad band but quite expensive. Low cost attenuators use lumped SMT parts that have higher parasitics and fall apart out of band.


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