choose a value for bandwidth of VGA and post amplifier

[matin-kh]

hi every one,
what is the relation between gain and bandwidth in two series amplifiers.
I have a VGA(Variable Gain Amplifier) which its gain is varying from -60dB to 0 dB i want to use a post amplifier in series with the VGA which its gain can be a value between 20db-30db and the bandwidth should be 6GHZ. I don't know how I should choose the bandwidth of VGA and post amplifier to approach this bandwidth! could you please help me?
with best regards
Matin

 

[chuckey]

I think you need to determine what bandwidth you want first. If your VGA is -3dB @ 6 GHZ and you need a bandwidth of 50 MHZ, (-3dB) then a 50 MHZ post amp would do. If your post amplifier has also a 6 GHZ -3dB then the final solution would be -6 dB at 6 GHZ.
Frank