ABSTRACT A harmonic‐included canonical section‐wise piecewise linear (CSWPL) model with both bias and frequency information is presented in this study. This new model is verified by means of fundamental and harmonic load‐pull simulation data for a 10‐W gallium nitride (GaN) packaged transistor considering a wide range of input power. According to the proposed model, the harmonic behavior of the device under test (DUT) can be captured more accurately than what is currently available in the existing fundamental‐only CSWPL model, which is very helpful for the designers of power amplifiers (PAs). Further, the proposed model is implemented in Keysight advanced design system (ADS) simulator by using a frequency‐domain defined device (FDD), which is then applied to the design of a single‐ended broadband PA. In accordance with the results achieved, the GaN‐based PA has a power added efficiency (PAE) greater than 60% and an output power greater than 40 dBm over the frequency range of 2 to 3 GHz. A very good match exists between the simulation results of the proposed model and the actual measurements of real PAs, which demonstrates the suitability of the presented model for practical PA applications.

ABSTRACT Gallium nitride (GaN) high electron mobility transistors (HEMTs) inherently demonstrate nonlinear behavior due to input capacitance modulation and bias‐dependent variations at elevated power levels, resulting in significant phase distortion and diminished intermodulation performance in power amplifiers (PAs). This paper presents a distinctive parallel R–C loaded matching technique aimed at mitigating these nonlinearities in GaN monolithic microwave integrated circuit (MMIC) PAs designed for frequency‐modulated continuous‐wave (FMCW) radar applications. The intrinsic device‐level sources of nonlinearity are examined, and the efficacy of the proposed network in suppressing amplitude‐phase (AM–PM) distortion and enhancing intermodulation distortion (IMD) characteristics is comprehensively assessed. Utilizing this technique, a 15–20 GHz three‐stage GaN MMIC PA is designed and simulated, achieving over 30 dB small‐signal gain, 23%–31% power‐added efficiency (PAE), and a peak power of 39.3 dBm at 17 GHz. The PA demonstrates excellent linearity, with AM–PM variation constrained within ±2° at saturation. The final design occupies a compact 3.37 × 2.59 mm 2 footprint, rendering it highly suitable for high‐throughput FMCW radar transmitters. Additionally, full electromagnetic (EM) co‐simulation, including quad flat no‐lead (QFN) packaging and bond‐wire parasitics, is conducted to validate performance robustness under practical integration constraints.

ABSTRACT This paper proposes a design method for broadband power amplifier (PA) using irregular matching structure based on an improved multi‐objective optimization algorithm, aiming at expanding its operating bandwidth. Initially, the gravitational search algorithm is enhanced by reconstructing the gravitational constant function for improving its global optimization capability. Subsequently, a fast non‐dominated sorting mechanism combined with a crowding distance strategy is introduced for multi‐objective optimization problems. Furthermore, to effectively overcome the bandwidth limitations that are inherent in conventional PA, the proposed multi‐objective gravitational search algorithm is employed for optimizing the irregular structure matching network. For verification, a broadband high‐efficiency PA is designed and fabricated, covering a frequency range of 0.4–4.0 GHz with a relative bandwidth of 163%. Measurement results show that the PA with the irregular matching structure maintains an efficiency of 59.1%–64.4% across the entire operating band, with a saturated output power of 40.3–41.8 dBm.

ABSTRACT Nuclear magnetic resonance (NMR) spectroscopy is a powerful technique for molecular analysis, yet its widespread use is limited by the bulky size and high cost of conventional radio frequency (RF) coils, which restrict portability and accessibility in clinical and field applications. To address this challenge, we propose a miniature birdcage coil implemented on a flexible printed circuit board (F‐PCB) with a Flame Retardant‐4 (FR‐4) substrate. The compact design, with a thickness of only 0.25 mm, enables the development of portable and user‐friendly NMR spectrometers without compromising performance. The coil generates a highly homogeneous magnetic field with 95% uniformity across a wide range of Larmor frequencies and achieves a magnetic field strength of 327 μT. Unlike traditional fixed‐frequency coils, the proposed design incorporates a programmable band‐pass function controlled by variable capacitors and a microcontroller, allowing electronic tuning across 1–13 MHz without hardware modifications. Finite element method (FEM) simulations confirm the coil's ability to maintain field homogeneity and high signal‐to‐noise ratio (SNR) over diverse operating conditions. Compared to existing RF coil designs such as planar, Helmholtz, or conventional birdcage coils, the proposed mini‐birdcage coil offers superior portability, tunability, and uniform excitation, thereby enhancing NMR signal acquisition and broadening applicability. This advancement holds promise for medical, pharmaceutical, biological, and geological applications, enabling portable NMR systems that improve diagnostic capabilities and expand accessibility in resource‐limited environments.

ABSTRACT To further enhance the precision of transistor modeling, the bidirectional long short term memory‐long short term memory (BiLSTM‐LSTM) neural network is utilized for the inverse modeling of the scattering parameters (S‐parameters) for the gallium arsenide pseudomorphic high electron mobility transistor (GaAs pHEMT) here. The modeling results show that the optimal mean square error (MSE) is up to 0.0001, the coefficient of determination ( R 2 ) is 0.9972 with the optimal mean absolute error (MAE) of 0.0049. Therefore, BiLSTM‐LSTM has superior advantage for the nonlinear relationship modeling for the S‐parameters of GaAs pHEMT.

ABSTRACT This study investigates interfacial heat transfer and phonon scattering effects in AlGaN/GaN heterostructures using a modified ballistic diffusive equation (BDE) that incorporates a radiative transfer formulation for quasi‐ballistic heat flux and integrates multiple phonon scattering models (Callaway, Born–Von Karman, Holland). Finite element simulations reveal that Umklapp scattering markedly reduces the effective thermal conductivity as both temperature increases and layer thickness decreases. A comparative analysis between Al 0.17 Ga 0.83 N and Al 0.32 Ga 0.68 N layers highlights distinct thermal conductivity trends, primarily due to enhanced boundary scattering in the higher aluminum‐content layer. The temperature distribution exhibits a pronounced peak within the GaN channel, followed by a rapid decline across the Al 0.32 Ga 0.68 N barrier, emphasizing the localized nature of heat generation. Overall, the results demonstrate that phonon scattering mechanisms and material composition have a decisive role in controlling phonon transport at nanoscale interfaces, providing essential insights to improve thermal reliability of GaN HEMT devices.

ABSTRACT Analytical models of base transit time for SiGe‐HBTs usually neglected carrier recombination in the base under the assumption of very thin base. The validity of this assumption is questionable under intermediate injection level (IIL) condition, which is common for highly‐scaled devices operating in the high‐current regime. However, consideration of recombination in the base along with various nonideal physical models reported in the literature under IIL condition leads to the analytical intractability of the governing differential equation (GDE). Therefore, this work intends to develop an analytically tractable ‐ model of SiGe‐HBTs applicable under IIL conditions. The model also considers the effects of base width modulation (BWM) on to simulate the effects of the base pushout phenomena usually occurred at high‐current regime. Close match of the simulated model data and experimentally measured data for the collector current density, total transit time, unity gain‐bandwidth cutoff frequency and maximum frequency of oscillation validates the model quite well. It is noteworthy that significant deviation from the measured data has been observed for the model that does not consider recombination at high‐current regime. Therefore, the proposed model not only provides the justification of the consideration of the effects of carrier recombination in the base to develop analytical model but also shows the practical significance of the developed model to guide the device engineers to design modern highly‐scaled SiGe‐based HBT devices operating in the high current regime, thereby meeting the requirement of sustainable industrialization to facilitate sustainable development goal 9 (SDG 9).

ABSTRACT Reconfigurable reflectarray antenna (RRA) has been considered a potential technology for future communication. However, few studies focus on investigating the intermodulation distortion induced by its active devices, which are employed to provide different compensation phases for the RRA elements. In this paper, the radiation pattern prediction for third‐order intermodulation (IM3) distortion of the RRA with embedded varactor diodes is first proposed. It is implemented with a nonlinear model of the varactor and full‐wave electromagnetism (FEM) simulation. The presented varactor model is first employed to design the RRA and then to acquire the power and phase of the IM3 signal in each element of the RRA, which is realized with a nonlinear harmonic‐balance and FEM co‐simulation. With the help of the HFSS software, the radiation pattern is achieved when the co‐simulation results of the RRA elements are input. The IM3 radiation measurement of the RRA is presented to verify the radiation pattern prediction of the IM3 signal. The consistent comparison results between the simulation and the measurement indicate that the proposed method is accurate. Significantly, the radiation pattern of the IM3 signal is different from that of the fundamental signal based on the designed RRA. It is meaningful and implies that it may have linearization approaches for the RRA. The proposed method will enhance the application of the RRA since the linearization approach is still a scientific challenge in future wireless networks.

ABSTRACT The domestic induction heating system comprises a heating coil and electromagnetic media (ferromagnetic cookware and a magnetic shielding layer). Horizontal or vertical misalignments between the heating coil and cookware during operation inevitably alter the coil's equivalent self‐inductance. This variation in self‐inductance affects impedance matching and complicates power regulation. Currently, calculations of this parameter rely mainly on finite element analysis (FEA) methods. However, FEA methods require significant computational time and may encounter convergence issues due to poor mesh quality, especially when simulating thin layers with large aspect ratios, where stringent meshing requirements often lead to non‐convergence near the surface. This work develops an extended analytical model that incorporates the finite size of the magnetic shielding layer and the finite conductivity of cookware materials (aluminum, 304 stainless steel, and 430 stainless steel). The proposed model accounts for variations in coil dimensions, the relative permeability of the magnetic shielding layer, and the conductivity of cookware materials. It achieves a computational speed five times faster than FEA simulations while maintaining an error of less than 5% compared to experimental results.