A New Approach for Angle-Selective Slabs: Theory and Design

A new approach for angle-selective slabs (ASSlabs) is proposed in this article. This approach employs an elliptic-function lowpass prototype (ELP) to achieve the characteristics of low-profile and high angular selectivity of ASSlabs. First, the ideal ELP mapping into the angular domain is demonstrated. Then, a realizable ELP based on a slotline-backed split-ring resonator (SRR) is proposed, with its elements optimized by the ideal ELP using a genetic algorithm. The parameters mapping between the unit cell and the equivalent circuit model (ECM) is constructed subsequently. Next, third-order and fifth-order ASSlabs with elliptic-function lowpass responses in the angular domain are designed. The third-order ASSlab is fabricated and measured to validate the correctness and synthesizability of the approach. The measured results show a roll-off rate of 0.50 dB/° in the transition band at the observed frequency of 6 GHz with a profile of only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.16\lambda _{\mathbf {o}}$ </tex-math></inline-formula>, and great frequency consistency is witnessed in the range from 5.6 to 6.4 GHz with a fraction bandwidth (FBW) of 16.7%. In addition, an enlarged roll-off rate of 1.16 dB/° is revealed by the simulated results of the fifth-order ASSlab with a profile of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.28\lambda _{\mathbf {o}}$ </tex-math></inline-formula>, illustrating the superiority of the proposed approach in designing low-profile ASSlabs with high angular selectivity.