why isn't this transistor getting any S21 gain when I have voltage gain also?

[skatefast08]

 

[FvM]

What's the idea behin plotting 1 - 10 GHz s-parameters of a transistor with 300 MHz transit frequency?

AC gain at 1 GHz is negative (-5dB) by the way, thus the heading assumption is wrong.

 

[PlanarMetamaterials]

Scattering parameters are not defined in terms of total voltages, so naturally your two definitions will differ. This difference is exacerbated by poor impedance matching, which you can see you have due to high S11 and S22.

I'm not sure what your DC block does, but I would guess it tends to look like an open circuit towards lower frequencies. This would allow significant voltage gain whilst not transmitting any power.

 

[FvM]

Both analysises are small signal, DC_block is treated as infinite capacitance. AC1.A is defined as Vout/Vin, thus both measurements are relative.