Help me design a quarterwave transmission line which will operate in two frequencies

I want to design a quarterwave transmission line which will operate in two frequencies 1.575GHZ and 2.68GHZ ? help me.

If it's a 50ohm line, yes.

If it's a transformer, I doubt it, but I don't know your circuit.

it is a transformer , which will transform the impedance from 100 ohm to 50 ohm.

How can one physical length respond to one electrical length (quarter-wave as you need) at two different frequencies?! I doubt it either.

You can use a Chebyshev impedance transformer, consisting of two lamda/4 transmission lines. The electrical length of each transmission line, 90 degrees = lambda/4, is set at (1575 + 2680)/2 = 2128 MHz.

Obviously you can not have a simple length of transmission line be 90 degrees at two different frequencies.

You could design a broadband matching network to cover both frequencies, as suggested above. There are lots of topologies.

You could use a quarter wave transformer, but centered between the two frequencies. That would give somewhat of a match at either frequency extreme.