how can I get the impulse responses of comparable amplitude ?

Hi ,
I am trying to design comb generator of 30 MHz to 1 GHz using multisim 12.0. I got the impulse response but its amplitude is decreasing as the frequency increases as shown in figure attached. What can i do to get smooth comb like output in spectrum analyzer?

There is no attachment.

However I think it is due to roll-off of sinc(freq)=sin(freq)/freq characteristics.

how can i solve this problem?

Curiously you didn't mention the circuit and respective pulse waveform used by your comb generator at all. How should we help?

To get a flat frequency response with - 3dB @1 GHz, the generator pulse width must be below 0.5 ns. Otherwise you need an equalization network.