cables -20 dB at higher frequencies above 8 ghz
cables -30 dB for frequencies below 1 ghz

Antennas,
-9.5 dB wide bandwidth
-20 dB narrow bandwidth
-6 dB ultra wide bandwidth

transmit antennas need better performance than receive antennas typically, so they don't damage themselves.

kch

-9.5 dB rtn loss = 0.5 dB inefficiency
-6 dB rtn loss = 1.25 dB inefficiency

My spec analyzer reads returns loss in 10log(Pf/Pr)  so a good cable has a more positive return loss... what is a good level (or resource) for return loss when calculated this way?

Pf is power forward
Pr is power reflected.

Positive vs. negative, hmmn depends on who's talking, however Return loss is always shown as a negative number on Agilent and Anritsu Network Analyzers.  I suppose your analyzer could show the word loss and have a positive number, but that isn't something I've ever seen before.

-10 dB says your power returned is -10 dB relative to the power forward.
Although if you say the word loss, as in return loss, then technically you can say its ten dB return loss, the word loss insinuates less than zero.
Your analyzer usually shows a -10 value. It's also the same as S21 in dB.

kch