Assume I have a YIG tuned oscillator (2-10GHZ), output power 10-20mW, and an ultra wideband antenna corresponding to this range. Is there a problem with feeding the antenna directly with the oscillator (using coax + balun if necessary), or is a "in-between" buffer needed ?

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    \$\begingroup\$ Well, if you take care of matching and whatnot, it should be OK. There will be some losses. At 10 GHz, there will be substantial losses in the coax. So the TX power will not be 10-20mW. \$\endgroup\$
    – mkeith
    Dec 17 '17 at 9:22
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    \$\begingroup\$ What is the YIG's tolerance for reflected energy? You may need some local "Pads" ---- 1 or 2 or 3dB inline attenuators, to bring VSWR close to 1.0 so the YIG is happy. \$\endgroup\$ Dec 17 '17 at 12:23
  • \$\begingroup\$ Unfortunately, most YIG's in Ebay are sold without too much spec these days. Anyway, can you explain how attenuators bring the VSWR close to 1.0? (I thought VSWR is related to impedance matching) \$\endgroup\$
    – MikeTeX
    Dec 17 '17 at 13:29
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    \$\begingroup\$ If you have source, pad, cable, load, the pad will always bring the impedance closer to 50 Ohms from the sources perspective. Imagine if it is a 20dB pad (not that you would use such a large pad). Most of the output energy is simply dissipated in the pad. Only a small amount makes it to the load. So the effective impedance is basically 50 Ohms (assuming a 50 Ohm pad). Another way to look at it is that the reflected energy is attenuated twice by the pad before it gets back to the source, so the reflection amplitude will be much less than without (measured at the source). \$\endgroup\$
    – mkeith
    Dec 17 '17 at 22:03

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