There are couple of baluns in the cadence libraries: ideal_balun in analogLib, balun in rfLib, etc. For balun in rfLib, we can specify the input and output impedance, while the ideal_balun we can not set any parameters.

I did a test for these components, a 50 ohm port is driving (ac coupled) the differential side of the balun while the single-ended side of the balun is loaded to another 50 ohm port to ground.

Simulation results show that the S11 and S22 depends on the input and output impedance we set for the balun. And ideal_balun results roughly matches the case where we set the input and output impedance to 50 ohm. It seems the trajectory of the ideal_balun is a bit longer.

In addition, if I plot real and imag part of Z11 and Z22, I got noise like output, to the number of T ohms.

Please help me understand these results. P-)

real(z11) plots