Coplanar Waveguide Bias T

Hello all

I am trying to design a Bias T using CPW transmission lines in CST microwave studio.
I am confused with the DC blocking.
Please have a look at the attachment.

I am using quarter wavelength coupled lines for blocking DC but on simulation the RF DC isolation gets worse on adding this DC block.

If I do not use any DC Block then RF DC Isolation is good (as low as -30 dB in the desired band) but when i insert the coupled lines for blocking DC the isolation is bad.

I referred to some research papers ...didn't find anything about coplanar bias t but there are papers on microstrip bias tee and in these papers I just see radial stubs and no dc blocks (series capacitor or coupled lines?)

Can someone clarify if i am making any conceptual mistake here?

thanks

Hi,

The radial stubs that were used for designing microstrip bias Tee are the quarter wavelength Tx lines.

-sv

Hello

Thanks for the reply.

Yes I kept the radius of radial stub as quarter wavelength and the point where 1st butterfly radial stub is inserted is also quarter wavelength from the T junction.
But I think quarter wavelength butterfly radial stubs help in choking RF

some type of DC block should be inserted between RF input port and the T junction. Is it not?
how can I achieve this DC blocking with tx lines?

Thanks