A bandpass filter with twin wideband channels in a single-layer guided-mode resonance grating is presented. Strong refractive-index modulation is used to support the excitation of multimode resonances TE1,0, TE1,1, TE2,0, TE1,2, and TE2,1, which are excited by the first and second diffraction orders, relate asymmetrical line shapes and broad low-transmission bands, where TE is the transverse electric. Taking advantage of narrow linewidth and sharp edge line shape in the spectra of TE2, (v is the mode), a bandpass filter with form factors of 0.61 and 0.7 for long- and short-wave channels is presented to demonstrate this concept.