matching between differential ports to differential ports

How is the matching carried out from one different port to another differential port?

For example, matching between output of balun (differential port) to another differential port (such as differential amp, or balanced antenna)?

Any suggestions or comments are very much appreciated.

As usual..
Divide your circuit by 2 and diff. impedances do your matching as usual..For instance let your diff. impedances be 100+j50 and 50-j30 Ohm
When you divide your circuit by 2, these impedances will also be divided by 2 , so you will do a matching between impedances 50+j25 and 25-j15 Ohm single ended.
Don't forget to tie the parallel components which are connected to virtual ground in series.

BigBoss, thank you for the insightful and helpful comments!

For the reserve problem, to find differential impedance from known single-ended impedances, your comments seem to suggest that, one can just use Z_diff=2*(Z_single1)? (where Z_single1, Z_single2 are the impedances for two single-ended ports that form a differential port). This also requires Z_single1=Z_single2 in order to do the doubling?

For another case, if one only has a 3-port S-parameter (balun for example), assuming port 1 is the single-ended input; port 2 and port 3 are the two single-ended outputs that forms a differential output. How does one find out the output's differential impedance? Any suggestion?