I am looking for an AC coupling capacitor (0603, if possible) with the lowest possible loss (we have a very weak signal) in the frequency band from ca. 200Mhz to over 2 GHz. I have a few unlabeled 10nF Caps in my drawer which perform significantly better than all others caps I have laying arround and I found out that a nickel plating can lead to higher losses. So which component should I try to get the lowest losses?