Mode converstaion: Connect coxial cable to differential PCB

[flanello]

Hello,

is there a method to estimate the mode conversation when a coaxial cable is connected to PCB with a differential circuit connected over a parallel strip line?

 

[BigBoss]

Using Balun ( it can be lumped or discrete depending on bandwidth) may be a solution.

 

[biff44]

Well, if you just solder a coax cable center and shield to a differential line...it will stink. If you put ferrite beads on the outside of the coax cable it will be a little better. Narrowband you can use a microstrip stub where the coax shield connects to keep currents flowing back on the outside of the coax. A balun is the correct way to do it.

 

[flanello]

Thanks for the information.
But there is no rule of thumb to estimate the effect?

 

[biff44]

If you were going from 1 to 3 GHz with such a thing, I would expect a 3 db insertion loss ripple, and maybe a return loss that went to 5 dB