The reason you may be getting less gain is that most signal generators have an impedance of 50ohms. A common base amplifier generally has an impedance of 20 - 50 ohms. You may be losing signal at the input of the amplifier.
I would probe the amplifier to see what actually makes it to the input and see if the individual stages offer enough gain.
Once you find what isn't working to specification, you can modify it.
I would probe the amplifier to see what actually makes it to the input and see if the individual stages offer enough gain.
Once you find what isn't working to specification, you can modify it.