Frequency selective rasorbers with wide passband have been investigated for the stealth of wideband antennas over the past few years. However, the wide passband degrades its in-band stealth performance. Therefore, in this work, a switchable wide-passband rasorber, whose passband can be switched into absorption band, is proposed utilizing a frequency-selective surface (FSS) and two resistive layers. First, a switchable second-order FSS is presented and the design of switchable resistive layer with wide passband is analyzed. Second, the reactance variation of the low- $Q$ resonator in switchable resistive layer during the switching process is investigated to elaborate its effects on the out-of-band absorption performance of rasorber. Third, a nonswitchable resistive layer is designed to improve out-of-band absorption. Simulated results indicate that in rasorbing state the proposed single-polarized device exhibits a passband from 3.5 to 4.8 GHz (31%) with insertion loss less than $-$ 1 dB and a low-reflection band from 0.93 to 7.16 GHz (154%). In absorbing state, the passband is eliminated and the device exhibits a wide low-reflection band from 0.96 to 6.85 GHz (150.8%).

Switchable rasorber has attracted a great deal of interest in recent years due to its in-band shielding ability. In this work, a methodology for designing a switchable rasorber with high roll-off and polarization selection characteristics is proposed. The device can be switched between rasorber, polarization selection and absorber modes, and composes of two resistive layers (a passive and an active resistive layer) and a frequency selective surface (FSS). Transmission zeros (TZs) are introduced in the FSS design to improve the roll-off characteristic of its transmission band. The PIN diodes on the active resistive layer and FSS can be independently controlled in the orthogonal polarizations to realize the polarization selectivity. The simulation results indicate that the device exhibits a 27.5% fractional transmission bandwidth (3.42 $\sim$ 4.51 GHz) under rasorber mode. In addition, the fractional absorption bandwidth is as large as 142.9% (1 $\sim$ 6 GHz) under absorber mode. A prototype is fabricated and measured to validate the proposed design methodology. This work is promising for designing metamaterials (MMs) with excellent flexibility and high performance.

The article deals with the low-sidelobe shaped-beam pattern synthesis (SBPS) problem under amplitude constraints, including the controllable dynamic range ratio (DRR) and the predetermined excitation amplitude. The formulated problem is nonconvex owning to the existing nonconvex constraints. To this end, a set of auxiliary variables are introduced to reformulate the original problem, and then a double-loop iterative algorithm based on the penalty dual decomposition method (PDD) framework is proposed. The proposed approach solves the reformulated problem by updating primal variables with block successive upper-bound maximization (BSUM) algorithm in the inner loop and updating the dual variables and penalty parameter with the constraint violation strategy in the outer loop. One important advantage of the proposed approach is that all of its subproblems have closed-form solutions, which guarantees that the reformulated problem can be effectively solved. Numerical simulations are carried out to validate the proposed approach’s superiority with both isotropic element pattern and active element pattern (AEP). The results show that the proposed approach can obtain a lower sidelobe level (SLL) and a smaller DRR when compared with the state-of-the-art approaches.

The investigation of dual-band frequency selective surface (FSS) has attracted a great deal of attention over the past few decades. However, the existing reconfigurable dual-band FSSs exhibit first-order responses with poor frequency selectivity. In this letter, a polarization-insensitive dual-band FSS with a rotationally symmetrical receiver-transmitter unit-cell configuration that exhibits a second-order response is presented. PIN diodes are loaded on separate layers to achieve the independent switching of two passbands. The full-wave simulation results are presented, and an equivalent circuits model (ECM) is also presented to analyze the operation principle of the proposed FSS. The measurement results of our fabricated prototype indicate that the device exhibits two independently switchable polarization-insensitive transmission bands centered at 3.06 GHz and 4.33 GHz. The shape factors representing the selectivity of the transmission band are 2.44 and 2.46 respectively, which are approximately 1/4$\sim$1/2 times that of the existing reconfigurable dual-band FSSs. The proposed FSS exhibits angular stability up to 40 degrees below 5 GHz. This work paves the way towards high selectivity reconfigurable dual-band FSS.