90 hybrid (quadrature) coupler S parameter Question

[mauro_provato]

Hello friends,
I am currently trying to design a hybrid 90o coupler (hfss13).
I am trying to obtain the S parameters of the four ports. The problem is that the simulation chart is much different from the theoretical chart. For example the theory deign's frequency is 3ghz, simulation shows 3.5 ghz

How can I set that port 4 is isolated??, port 1 is input etc? Is it necessary? (I used lumped ports)

Please take a look on my projects and on the charts.

Thank you for your time and assistance.

 

[eraste]

Hy,

Well, i have looked your shematic. It seem to me that, on your branchline, you have just put the four lambda/4 lines without optimize your system.It is evident also that the simulation give you a higher frequency. In fact, when you connect your four lines it appears that this line are less long than your lambda/4 calculated for 3 GHz. So you must have to introduce 1 variables like L1+epsilon for a first couple of line at Zc1 (L1 fixed = lambda/4 at 3 GHz , epsilon a very small variable) and L2+epsilon for the second couple of line at Zc2 (L2 fixed = lambda/4 at 3 GHz, epsilon the same very small variable). Indeed, optimize epsilon in order to have dB(S12)=3 dB or phase(S12/S13)=90°.
Plus i suggest you to add four acess lines to your branchline coupler.

Good simulations.