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.