▎ 摘　　要

We show that the even order ungated modes can be excited under normal incidence while the odd order ungated modes cannot in traditional single-side grating-gate graphene field-effect transistors. The odd order ungated modes will suppress the excitation efficiency of the gated modes. In order to realize multiband detection by effectively exciting the higher order gated modes, the frequency of the 1st order ungated mode should be tuned up, which can be realized by shortening the length of the ungated region. We propose to use the dual-side grating-gate structure to shorten the length of the ungated region. Gated mode up to 21st order can be realized in complementary dual-side grating-gate structure. The ultra-multiband absorption can be actively controlled to cover 1.06-10 THz when the graphene Fermi energy is tuned from 0.2 eV to 0.6 eV. Even order gated modes will be excited by gradually overlapping the two grating layers because of the break of symmetry. Broadband detection from 0.1-8.2 THz can be realized by the effective excitation and overlap of the odd and even order gated modes.