In this paper, a metamaterial polarization converter which can transform linearly polarized (LP) wave into its orthogonal polarization in the microwave region is designed and realized for the simultaneous implementation of the reflection and transmission polarization conversion. The special polarization converter is composed of dielectric substrate sandwiched by the split-ring resonator and the slotted PEC ground. The simulation results demonstrate that the reflection cross-polarization of this converter has a significantly polarization conversion ratio (PCR) over 90% in the frequency bandwidths of 23.50-32.31 GHz, and the transmission cross-polarization of this converter has a high PCR over 95% at frequencies of 7.78 and 13.39 GHz for normal incident LP waves. The simulation results are in good agreement with the experimental ones. Furthermore, the property of reflection and transmission cross-polarization of this proposed converter is stable at low frequencies with incident angle up to 50°. The physical mechanisms of the proposed multifunction polarization converter can be elucidated by the electromagnetic resonant theory based on its current distribution. The proposed polarization converter can be functionalized by changing the parameters of the slotted PEC ground, which has a great potential to be used as a selective polarization filter.
An ultra-broadband double-layer microwave metamaterial absorber (MMA) with reflectivity below À10 dB ranging from 1.4 to17.31GHz is presented in this article. The MMA has a fractional bandwidth of 170% and a total thickness of 20.8 mm. By analyzing the function of different layers, the MMA can be simplified to the combination of a dual-band (DB) absorber and a single-band (SB) absorber. Layer I consists of a square loop loaded with asymmetric resistors and achieves a DB absorption by exciting high-order modes covering the low-frequency and high-frequency. Layer II is composed of double-ring structures integrated with resistors and realizes an SB absorber in the middle frequency. To understand the physical mechanism in detail, the equivalent circuit model (ECM) is proposed and illustrates a good impedance match within the entire absorption bandwidth with free space. An in-depth analysis has been carried out by illustrating several key dimensions. To verify our idea, a prototype has been designed, fabricated, and measured. Measurement results show an ultra-broadband absorption with the reflectivity below À10 dB ranging from 1.7 to 17.27 GHz under the normal direction, which agrees well with simulation and ECM results.
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