LTC2274 Front end

We are designing ADC front end design circuit for LTC2274 with low insertion loss (loss  <5dB between 1MHz and 30MHz).

I simulated the typical application circuit provided in data sheet using S-parameter for the ADC part LTC2274, s-parameter for transformers and implement other discrete components as provided in the data sheet. Result obtained for that circuit, insertion loss is >16dB (Refer below table for insertion loss and return loss measured for different frequency)

Frequency

Insertion loss

Return loss

1MHz

-21.865

-7.913

5MHz

-21.444

-7.113

10MHz

-20.482

-7.005

15MHz

-19.561

-7.101

30MHz

-16.715

-7.737

In data sheet it is stated that, recommended to have a source impedance of 100 Ohm or less for each input. The source impedance should be matched for the differential inputs.

While simulating, i am getting more than 450Ohm impedance obtained at 30MHz.(S2P file directly terminated to 100Ohms and obtained 450Ohm, suspecting any error in s2p file. Attached s2p file for referenceLTC2274 FULL CLK 105MSPS 1-2 S2P.S2P)

Shall I use datasheet mentioned front end circuit of (1MHz to 70MHz) for my application, otherwise I need to change.