how to simulate differential LNA

Hi

Iam having problems with differential Lna simulation in spectre. I have designed a matching network that would step down the impedance to a low level . After that i have used an ideal balun from the rf lib and tried to simulate it. I also tried with a VCVS.Neither of these seem to work. My S21 is a straight line .

BTW the impedance transformation network is a sttepped capacitor network.

Any sugeestions or documents that show details of simulation and calculation of matching network for differential LNA would be appreciated.

The same circuit in a single ended version works just fine

Please help.
thanks