The reconfigurable intelligent surface (RIS) is a promising route for the next generation of communication and has been widely investigated. The research on its nonlinear electromagnetic (EM) phenomenon has been reported extensively. However, few researchers focus on the quantitative analysis of the nonlinear distortion of the RIS due to the active components serving as the tuning devices in its unit cells. A method of assessing the third-order intermodulation of RIS is proposed in this article, which is implemented with a combination of the nonlinear active device modeling and full-wave simulation of the passive part of the RIS. Considering that the varactor diode is widely utilized, a nonlinear equivalent circuit model is proposed in this article. It contains an improved capacitance–voltage model with an m expression acquired with the nonlinear current calculation. The nonlinear diode model is used to form the meta-atoms in the RIS system to realize nonlinearity assessment. Several characteristics of the diode are measured, and the measurement data are employed to verify the accuracy of the nonlinear modeling work for the varactor diode. More importantly, consistent comparison results are also obtained from the nonlinear assessment of the RIS system, which indicates that the proposed method is precise. With the nonlinear modeling work of the RIS system, much analysis can be carried out. For example, we can study the nonlinear characteristics of each meta-atom to improve the linearity of the RIS system. Consequently, it demonstrates that the proposed assessment method is significant.

Excellent linearity performance is one of the merits of the p-i-n diodes. However, high linearity is achieved by operating in the high reverse-bias (off-state) and high forward-current (on-state) conditions. This article aims to address these problems by proposing a nonlinear p-i-n diode model to investigate the nonlinear characteristics of the diode when reducing the reverse bias and forward current. The benefits include decreased supply voltage and reduced power dissipation. For reverse bias, a calculation based on the Poisson equation is proposed for the reverse capacitance. It combines the proposed reverse resistances in the ${\textsc{off}}$ -state to account for the unexpected intersection points observed under varying ambient temperature conditions. According to this phenomenon, the device exhibits good linearity at higher temperatures than at lower ones. It is interesting and has been successfully modeled, as evidenced by consistent verification results. In general, the slope of a p-i-n diode’s third-order intermodulation (IM3) power with respect to the input power is usually supposed to be about 3. However, the case changes when the forward current decreases, and the slopes of the IM3 signals decrease with increasing input power. It appears that the linearity of the diode improves with increasing input power. To model the phenomenon, a capacitance is proposed in shunt with the on-state resistance path for the transmission of radio frequency (RF) signals, which should be the diffusion capacitance of a p-i-n diode. This article first describes the linearity benefits of the capacitance for p-i-n diodes. These outcomes indicate that the proposed nonlinear model is significant for p-i-n-diode-based nonlinear circuit design, particularly for applications requiring low forward current and reverse voltage conditions.

A novel enlarging fractional bandwidth (FBW) technique for acoustic‐wave‐lumped‐element resonator (AWLR)‐based bandpass filters is presented. The new technique is based on a series of matching inductors that replace the parallel or series acoustic wave (AW) resonators of AW filters to beak the bandwidth constraint of the ladder‐type structure. In addition, the transmission response analysis of the proposed AWLR‐based filter is provided. A prototype of the AWLR‐based filter is fabricated and tested to validate the proposed FBW widening technique. The measured insertion loss, FBW, and out‐of‐band rejection are 1.5 dB, 1.63 k _t ² ( k _t ² is the electromechanical coupling coefficient of the AWR), and 38 dB, respectively.