balun dc feed

I know a balun is a three-port device, one unbalance input and two balance output. The two balance outputs have the same magnitude of signal with 180 degree phase difference. But I find that there exist DC feed in some balun products. I don't know what they are used for. Who can explain it to me? Thx in advance.

maybe it is a active balun
then you need power

you're right, It needs power. Then how does the dc feed affect the performance of the balun?

That depends on the design of the balun
I do not know yet

I can give you the paper from the IEEE which I am puzzled about. If I post it here, it's charged and I don't know how to set it free. So maybe I can send it to you by email. OK? Mine is ye_zhongh@yahoo.com.

I do not think active balun with out gain.
The reason could be based on the next stage level requirement.

The DC feed is basically used to feed with DC the balanced inputs (or outputs) and should have minimal effect on the balun performance. Of course, those feeds/teeminals can play a vital role if they are used in the impedance transformation, but 50:50 Ohm conversion will actually require AC gnd for those nodes...

--padpan