No coupling capacitor?

hello everyone, i came across a paper on distributed amplifer and they havent used any input coupling capacitor in their design. so is the design practical without using coupling capacitor. here is the link to the paper

http://www.ecti-thailand.org/assets/...235_pub_17.pdf

and here is the design itself

Hello
and what is your question?

The circuit needs coupling capacitors at the input, and also at the output.

so it means this design is wrong?

No, is not. Just didn't show those caps.

can we calculate s parameters without this coupling capacitor and assume that it would be off chip?

S parameters must be calculated considering coupling capacitors, where they could be on or off chip, because S parameters performance is changed by adding an element, mainly S11 and S22 respectively. On the other hand, is your intention is to get amplifier performance, you can assume ideal capacitors, but they must be considered for physical implementation.

Yes, if the freq is not high and the inductance of the capacitor is very small, the capacitor can be neglected.

i m working on 0.1G to 2.7GHz, can i neglect? cuz im designing a distributed lna, and even if i add coupling capactior at input in the basic distributed topology the gain s21 gets negative,