A novel triple-band frequency selective surface (FSS) as a band stop filter in Global System for Mobile communication (GSM) frequencies is presented. Unit cell of the FSS consists of two isolated resonators, one square loop resonating at 942 MHz and another synthetic resonator in the same layer having resonant frequencies of 1842 and 2142 MHz. The synthetic resonator consists of two similar geometries which are coupled to each other by slim gaps in a way that each resonance arises through the joint lengths of both of the geometries. Therefore, these dependent resonators simply provide frequency tuning ability in those very closely spaced frequencies. Moreover, very low-frequency response sensitivity to the oblique incidence angles is achieved by using a miniaturized single synthetic resonator for the two frequencies in a single layer. A desirable 20 dB attenuation in the transmission characteristics is achieved at all frequencies of the GSM system with stability for oblique incidence for both TE and TM polarizations.