The quest of novel materials and structures to design an efficient absorber for realizing wave trapping and absorption at terahertz (THz) frequencies is an open topic. But the design of a thin, wideband and tunable THz absorber is still an arduous job. Hence, in this work, a hybrid THz metamaterial absorber (THz-MMA) integrated with a cascaded graphene frequency selective surface (FSS), with ultra-high absorbance over a wide frequency range is designed using an analytical equivalent circuit model (ECM). A systematic study and critical analysis over a wide range of device parameters including graphene chemical potential and FSS design variables is demonstrated. A peak dip in reflection coefficient (RC) of -30.27 dB is observed at 2.94 THz for an optimal device with a chemical potential $\rm (\mu_c)$ of 0.38 eV $\rm (\mu_{c1})$ , and 0.25 eV $\rm (\mu_{c2})$ . The cascaded FSS configuration results in unique anti-reflection based absorption phenomena, which is responsible for the achievement of -10 dB absorption bandwidth of 2.34 THz (0.85-3.19 THz). In addition, the frequency dependent effective permittivity, permeability and impedance is extracted using reflection data, in order to understand the device physics. Such ultra-thin and broadband absorbing device architecture may confer potential application perspectives in THz sensing, imaging and detection.

A tri-band shared-aperture antenna array is proposed in this letter. Band-1 (3.76–4.76 GHz) and Band-2 (5.20–6.45 GHz) antennas are designed such that the structure of one band exhibits a surface-wave electromagnetic bandgap (SW EBG) characteristic for the other band, thereby enhancing inter element isolation when arranged in a triangular 2×4 shared array. Two heterogeneous Band-3 (14.75–15.25 GHz) elements— a microstrip patch and a substrate-integrated waveguide (SIW) cavity slot antenna—are designed and integrated into the Band-1 and Band-2 antenna structures, respectively. Each unit-cell of the Band-1 structure contains four Band-3 patches, while each Band 2 unit-cell incorporates one Band-3 SIW slot antenna. A prototype of a 2×4 shared-aperture array consisting of Band-1 and Band-2 elements with 128 (only 1×8 populated for testing) Band-3 elements is fabricated and tested. Good agreement between simulated and measured results is observed. For the single element, the simulated -10 dB reflection bandwidth of 23.5%, 21.5%, and 3.4% is achieved with peak gains of 10.7 dBi, 9.2 dBi, and 5.5 dBi in Band-1, Band-2, and Band-3, respectively.