This paper presents improved quad-mode resonators based on the open/short-end load of the center stub. which introduces the self-coupled structure. Compared with the traditional stub-loaded stepped impedance resonator (SLSIR). the proposed quad-mode resonators can significantly reduce the circuit size and further increase the design freedom. https://www.roneverhart.com/Western-Digital-Ultrastar-DC-HC570-WUH722222ALE6L4-0F48155-22TB-7-2K-RPM-SATA-6Gb-s-512e-SE-3-5in-Refurbished-HDD/