Improve the Insertion loss of a 1st order Polyphase filter

I am designing a Polyphase filter as the main block for my Quadrature phase generator.

I am using the 1st order polyphase filter to check how much insertion loss can be expected before I fix the design. After the SP analysis I got an insertion loss of(S21 = 7.6dB) 

I have attached the circuit I used and the testbench. What can do to improve my testbench to get a lower insertion loss (~ 4dB)?