surface current on spiral antenna

hi everybody,
does anyone know that what would change the direction of surface current on antenna?please help me its so necessary.

This is very general question.
The surface current is formed from the shape of the radiator, if no radiator there will be no surface current, and this is apply to antenna which the radiator is metal or copper. But the surface current flow for general antenna ( eg:patch) are very well defined in books.

i design a spiral antenna by cpw fed, i want to know that could i change the direction of surface current by different feeding method?

I assume that you want current cancellation on certain point of your antenna or you want to increase performance for some parameters on your antenna.

Basically you have a CPW connect to source and another with ground, and most likely all the feeds for antenna are based one this. I can't think anything that would help you to change the current flow.

i want to change the current from clockwise to counter clockwise and wise versa to increase circular polarization

well the other you can do feed it at different point, like a circular polarized patch antenna.

i should mention that i use a cpw to microstrip feed line, before this i use a cpw feed and the antenna parameters was good , but after using this transition they degrade.now what should i do in this case?

then have you check the impedance of this transition. CPW to microstrip feed, are there any mismatch? Check this and how the S11 change with and without microstrip feed.

the matching is somehow good,s11 is below -10 dB

If the gain and efficiency is similar as well, then there is disruption in current somewhere in your feed. If you did this design in CST, probably you can send to me I can have a look and the snapshot of your surface current before and after microstrip feed.

the gain and radiation pattern are degraded and just the s parameter is good

antenna is determined more by radiation pattern (gain and efficiency) rather than S11 as normally we consider.

My last resort will be, check the impedance again. If you able to recall EM theory (on plane wave theory), impedance and EM field are co-related. There should be a miss-match in your impedance between cpw to mstrip line, or mstrip line to antenna (not a lot) and this cost small reflection which effect the gain and eff and not S11 , tune or optimize your CPW or Mstrip line to get your desired goal. On the other hand you never change anything, you just add Mstrip line, where else could go wrong.

sorry may i have your email to contact with yourself