Ultra-wideband and Wide-angle Insensitive Absorber Based on TCDA-under-TCDA (Tightly Coupled Dipole Array)

In this paper, an ultra-wideband and wide-angle insensitive absorber is proposed. The unit cell of the proposed structure consists of a tightly coupled dipole array (TCDA2) under another TCDA (TCDA1) that is twice the height of TCDA2 (TCDA-under-TCDA structure). TCDA1 of the unit cell acts as either a lossless (or lossy) antenna when the frequency is out of (or in) the operating frequency range of TCDA2. Reciprocity is applied to design TCDA1 as an absorber when the frequency is out of the operating frequency range of TCDA2 (lossless antenna region). On the other hand, the multi-section impedance matching technique is applied for TCDA1 to be an absorber when the frequency is in the operating region of TCDA2 (lossy antenna region and reciprocity cannot be applied). In addition, a meta-surface (MS) and vertical metal strip (VMS) are employed to develop the wide-angle insensitivity absorber. A.10 dB reflection bandwidth of 0.63 - 6.55 (10.4:1) is achieved with a 0.126 λlow at the lowest operating frequency under normal incidence. The bandwidth is moderately reduced to 0.69 - 6.75 (9.78:1) with a 0.138 λlow for the TE mode and 0.75 - 6.22 (8.29:1) with a 0.150 λlow for the TM mode under 45° oblique incidence. The measured results of the fabricated absorber using the transverse electromagnetic (TEM) cell are in good agreement with the simulated results.