This article presents a multifunctional dual-band energy selective surface (ESS) based on a two-layer resonant circuit model with high-power microwave (HPM) protection ability for two bands. An equivalent circuit model (ECM) engineering multiple stopbands and passbands with combinations of parallel and serial resonators is proposed for dual-band design. By loading diodes in the resonator accordingly, the operating band can be switched from low insertion loss (IL) state to high shielding effectiveness (SE) state power-dependently. Additionally, the independence of two bands is greatly improved by utilizing two separate layers to mount the diodes, attributing to the enhanced difference of induced voltage between diodes in different layers resulting from shielding effect of top layer. Various functions in two-frequency co-incidence scenarios are analyzed, demonstrating the advantage of independent modulation. Based on the ECM, a two-layer ESS is designed. Two wide bands with IL<1dB under low-power incidence and SE>20dB under HPM are achieved, due to second-order resonance produced by double-layer configuration.  The multiple nonlinear functions of the design are verified by field-circuit co-simulations. Several prototypes are measured, exhibiting 0.6&25.2 dB and 0.7&27.3 dB of IL&SE at two central operating frequencies for low-power and high-power incidences, respectively, with good agreement with the simulations.

In this letter, a novel model for broadband power amplifier (PA) linearization is proposed, namely Attention Mechanism based Bidirectional Long Short-term Memory network (AM-BiLSTM). In order to verify the linearization performance of the AM-BiLSTM model, a 100MHz bandwidth 5G new radio (5G NR) signal is employed to test the sub-6G PA operating at 2.6-GHz. The experimental results show that the adjacent channel power ratio (ACPR) of the PA with AM-BiLSTM can be improved by 24dB which is 6-dB better than the generalized memory polynomial (GMP) and 3-dB better than the Chebyshev polynomials LSTM (CP-LSTM) in ref[1]. Therefore, the proposed AM-BiLSTM is very effective for the linearization of broadband PA.