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1. A Highly Efficient Dual-band Harmonic-tuned GaN RF Synchronous Rectifier with Integrated Coupler and Phase Shifter

   https://doi.org/10.1109/MWSYM.2019.8700900  

   Hoque, Md Aminul; Ali, Sheikh Nijam; Mokri, Mohammad Ali; Gopal, Srinivasan; Chahardori, Mohammad; Heo, Deukhyoun (June 2019, 2019 IEEE MTT-S International Microwave Symposium (IMS))

   This paper presents a dual-band RF rectifying circuit for wireless power transmission at 1.17 GHz and 2.4 GHz. A dual-band harmonic-tuned inverse-class F/class-F mode power amplifier using a 10 W GaN device has been utilized to implement the proposed rectifier with an on-board coupler and phase shifter. The matching circuit is precisely designed so that the circuit operates in inverse class F and class F mode in the lower and upper frequency bands using dual-band harmonic tuning, respectively. Measurement results show that the rectifier circuit has 78% and 76% efficiencies at 1.17 GHz and 2.4 GHz frequency bands, respectively. To the best of the authors' knowledge, this rectifier is the first demonstration of a dual-band harmonic-tuned synchronous rectifier using a GaN HEMT device with an integrated coupler and phase-shifter for a watt-level RF input power. 

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2. Polarization‐Engineered GaN‐Based High‐Electron‐Mobility Transistors for High Power RF Applications

   https://doi.org/10.1002/pssa.202500132  

   Jeng, Yu‐En; Venkatesan, Nivedhita; Xu, Pengcheng; Wu, Weifeng; Zhu, Zhongtao; Fay, Patrick (December 2025, physica status solidi (a))

   Gallium nitride (GaN)‐based high‐electron‐mobility transistors (HEMTs) are advantageous for power RF applications due to their dense 2DEG and high mobility. However, at mm‐wave frequencies, the lateral scaling required to achieve high‐frequency operation reduces breakdown voltage, limiting output power. Polarization grading of the barrier offers a solution by enhancing both RF performance and breakdown voltage. This study evaluates nonlinear grading profiles, which improve power handling without the need for additional field plates. Simulations using Synopsys Sentaurus technology computer‐aided design (TCAD) reveal that polarization‐graded HEMTs, featuring a graded AlGaN barrier layer (6–18 nm), exhibit more negative threshold voltage, increased drain current, and flatter transconductance compared to conventional abrupt‐interface HEMTs. The graded layer reduces peak lateral electric fields by as much as 39%, resulting in breakdown voltages that are 2.2 times higher than reference HEMT structures without grading. Polarization‐graded HEMTs with an 18 nm graded layer achieve a maximum output power of 8.8 W mm⁻¹, nearly three times that of conventional HEMTs. These results demonstrate the potential of polarization‐graded structures for mm‐wave applications, enhancing intrinsic field and power‐handling capabilities. 

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3. High-k, Low-Loss Ceramic-Thermoplastic Composite Feedstock Filaments for Fused Deposition Modeling of Microwave and mm-Wave Devices

   https://doi.org/10.5772/intechopen.1008537  

   Kosamiya, Vishvajitsinh; Wang, Jing (January 2025, IntechOpen)

   Maturing of additive manufacturing (AM) techniques has increased their utilization for fabricating radio frequency (RF) and microwave devices. Solid composites used in material extrusion AM have experienced considerable expansion over the past decade, incorporating functional properties into 3D-printed objects. There are encouraging indications from AM material research that electrically efficient AM materials can be discovered. These materials would be useful for producing microwave components in the future. One of the enabling techniques for fabricating these materials is to incorporate nano/microparticles or fillers into thermoplastic material. Composite material 3D printing is a novel approach to managing materials’ microwave properties. While extrinsic qualities (effective permittivity) can be controlled by shape and porosity management, intrinsic attributes are tied to the composition of composites. Furthermore, combining various materials to increase the spectrum of available microwave characteristics is made possible by multi-material 3D printing. In this chapter, we explore different methodologies to fabricate ceramic/thermoplastic composites for fused deposition modeling (FDM) of RF and microwave devices. Analytical models for predicting effective permittivity of the composite are discussed and application examples of FDM printed RF, microwave and mm-wave devices employing composites are presented. 

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4. Directional Multi-Band Planar Monopole Antenna with Parasitic Director

   Perez-Pinon, Anthony; Chung, Nathan; Volakis, John (July 2026, IEEE)

   This paper presents a compact planar (~ 𝝀/𝟑 in electrical length), directive and multi-band antenna that also exhibits a mono-directional radiation. The antenna is coupled to a tree-like shaped parasitic element and has a single feed exciting a meandered line that generates multiple resonances. It supports 5.8GHz, 7.7GHz, 9.6GHz, and 10.9GHz bands. The antenna is geometrically planar in the XY-plane, and its radiation beam is along the surface normal in the -z direction (mono-directional). The parasitic tree acts as a director to enhance the broadside (along the -z direction) radiation, yielding an improved directivity as compared to that conventional planar dipole and monopole antennas. Notably, operating within the 5.8GHz-11GHz microwave band supports applications in sensing and communications within the ISM and X bands. Benefits of the antenna include reduced susceptibility and radiation control, enabling a strong balance between performance, bandwidth, and system level integration for directional RF platforms. 

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5. XHEMTs on Ultrawide Bandgap Single‐Crystal AlN Substrates

   https://doi.org/10.1002/aelm.202500393  

   Kim, Eungkyun; Chen, Yu‐Hsin; Pieczulewski, Naomi; Encomendero, Jimy; Muller, David Anthony; Jena, Debdeep; Xing, Huili Grace (February 2026, Advanced Electronic Materials)

   ABSTRACT AlN has the largest bandgap in the wurtzite III‐nitride semiconductor family, making it an ideal barrier for a thin GaN channel to achieve strong carrier confinement in field‐effect transistors, analogous to silicon‐on‐insulator technology. Unlike /Si/, AlN/GaN/AlN can be grown fully epitaxially, enabling high carrier mobilities suitable for high‐frequency applications. However, developing these heterostructures and related devices has been hindered by challenges in strain management, polarization effects, defect control, and charge trapping. Here, the AlN single‐crystal high electron mobility transistor (XHEMT) is introduced, a new nitride transistor technology designed to address these issues. The XHEMT structure features a pseudomorphic GaN channel sandwiched between AlN layers, grown on single‐crystal AlN substrates. XHEMTs demonstrate RF performance on par with the state‐of‐the‐art GaN HEMTs, achieving 5.92 W/mm output power and 65% peak power‐added efficiency at 10 GHz under 17 V drain bias. These devices overcome several limitations present in conventional GaN HEMTs, which are grown on lattice‐mismatched foreign substrates that introduce undesirable dislocations and exacerbated thermal resistance. With the recent availability of 100‐mm AlN substrates and AlN's high thermal conductivity (340 W/), XHEMTs show strong potential for next‐generation RF electronics. 

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