Nonlinear Analytical Model of Localized Sub-THz and THz Rectifications in FET Power Detectors

<div>A nonlinear analytical model for THz FET power detectors based on their distributed RC network is presented. This empirical model works well for both drain-unbiased and drain-biased THz FET responses. The physics-based analysis reveals that localized THz rectifications in long channel transistors may be mathematically expressed in the same way as regular RF frequency rectifications of a single lumped device. However, the one lumped FET model can’t work properly at THz frequencies without correct definitions of THz signals on its terminals and independently considers localized rectifications on the source and drain sides. An improved compact one lumped THz FET power detector model with additional Schottky diodes at the source and drain terminals is presented. THz FET detector can also perform a simultaneous self-amplification (active rectification) of the localized THz rectified dc signal when operates in the saturation regime beyond its unity gain frequency. A novel analytical expression for the localized THz dc rectified response is developed for FETs operating in the saturation regime. The presented physics-based model agrees excellently with the measured experimental results of GaAs HEMT transistors at 1.6THz under arbitrary biasing conditions. Many novel electronic designs can be implemented for Millimeter-wave and THz technologies based on the physical FET's nonlinear nature in this frequency range</div>

Nonlinear Analytical Model of Localized Sub-THz and THz Rectifications in FET Power Detectors

<div>A nonlinear analytical model for THz FET power detectors based on their distributed RC network is presented. This empirical model works well for both drain-unbiased and drain-biased THz FET responses. The physics-based analysis reveals that localized THz rectifications in long channel transistors may be mathematically expressed in the same way as regular RF frequency rectifications of a single lumped device. However, the one lumped FET model can’t work properly at THz frequencies without correct definitions of THz signals on its terminals and independently considers localized rectifications on the source and drain sides. An improved compact one lumped THz FET power detector model with additional Schottky diodes at the source and drain terminals is presented. THz FET detector can also perform a simultaneous self-amplification (active rectification) of the localized THz rectified dc signal when operates in the saturation regime beyond its unity gain frequency. A novel analytical expression for the localized THz dc rectified response is developed for FETs operating in the saturation regime. The presented physics-based model agrees excellently with the measured experimental results of GaAs HEMT transistors at 1.6THz under arbitrary biasing conditions. Many novel electronic designs can be implemented for Millimeter-wave and THz technologies based on the physical FET's nonlinear nature in this frequency range</div>

Analysis of the electromagnetic wave illumination on the transmission lines with nonlinear terminations

In this paper, an unconditionally stable time-domain method is proposed to investigate the external electromagnetic (EM) field illumination on the nonlinearly loaded transmission lines. In the proposed algorithm, the field to line coupling equations and linear/nonlinear boundary conditions are incorporated and expressed in a matrix form. The derived differential matrix equations are then discretized and solved using the proposed finite difference time domain (FDTD) method approach. The discretized nonlinear matrix equations are also solved by applying a globally convergent iterative method to ensure the stability of the method. Moreover, the experimental investigations are conducted using a transverse EM (TEM) cell for a single microstrip line and a power detector circuit as a nonlinearly loaded transmission line to confirm the accuracy and stability of the proposed method. With the merit of satisfactory accuracy and unconditional stability for the entire range of time steps, the presented approach would be applicable for analyzing the microwave linear/nonlinear circuits subjected to the external incident EM wave.