ATC 400 Z Series Precision Tolerance NPO RF Microwave Capacitors. The 400Z series Precision Tolerance, Thin Film, NPO RF Microwave capacitors is constructed with a low loss silicon dioxide and silicon oxynitride dielectric along with high quality sputtered electrode materials to ensure superior performance. The 400Z series offers the tightest tolerances available over a wide range of capacitance values. Typical applications include Filter Networks, Matching Networks, Hi-Q Frequency Sources, Tuning, Coupling, Bypassing, and DC Blocking.