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Help in Lange Coupler Design

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sv1437

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Hi,
I designed a 4 finger Lange Coupler in Ansoft Designer 4.0 with fo=2.5GHz.

Port 1: Input Port Port 2: Isolated Port Port 3: Coupled Port and Port 4: Direct Port.

I was able to achieve good reflection loss (|S11|dB >20) and good Isolation loss.
And good coupling to the direct port (|S41|dB < 3dB) but the transmission to the coupled port (|S31|dB > 6dB) suffered.

I tried to change the length of the conductors, width of the conductor strips and the spacing between conductors but nothing seem to improve the coupling between the input port and the coupled port (|S31|).

Can you please suggest me is there any way that I can improve |S31|.

And one more question, which parameters should I change to increase the bandwidth. I read in some of the IEEE papers, that increasing the number of fingers increases the bandwidth but decreases the coupling.

Thanks,
Subash.
 

sv1437

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I used the same document as my reference. I followed the steps that are given for designing my Lange Coupler. That document does not have any information, like what to modify if the coupling is not 3dB.
 

sv1437

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I did parametric analysis on almost all the parameters of the Lange Coupler. Width of the conductors, spacing between the conductors, metal thickness with dielectric thickness constant. No improvement is seen between the input port and coupled port. Can anyone suggest some design ideas?
 

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