This letter presents the large-signal performance degradation of 0.1- mu m AlGaN/gallium nitride (GaN) high-electron-mobility transistor (HEMT) on silicon carbide (SiC) substrate after continuous high-power stress at 60 GHz over two days for V-band transmitter applications. The devices were evaluated under extremely high frequency (EHF) continuous wave (CW) operation in a class-AB power amplifier (PA) configuration at room temperature. It is reported that the gate current remained stable over the time, but poststress measurements indicated a significant reduction in gain, output power (P-out), and power added efficiency (PAE) at P-1 dB , P-2 dB , and P-3 dB input power levels. The same devices were also subjected to dc stress conditions for five days. Furthermore, numerical analysis shows that degradation is attributed to trap generation caused by the hot electrons, primarily affecting the intrinsic parameters of the device, which is critical for V-band operation in baseband transmitter systems.

In this study, AlGaN/GaN high-electron-mobility-transistor (HEMTs) with a small gate length were fabricated using a stepper. Additionally, a novel gate fabrication process was conducted to shrink the gate head, thus reducing the parasitic capacitance of the device to achieve high-power amplifier performance. The device performance in the research demonstrated a steady-state current density (I-dss) of 975 mA/mm and a maximum transconductance (g(m)) of 369 mS/mm at a 20 V bias. Moreover, the cut-off frequency (f(T)) reached 50.6 GHz, and the maximum oscillation frequency (f(max)) achieved 161 GHz as measured by S-parameter measurement. In the load-pull system, the frequency operation is under 28 GHz. For the 2 x 50 mu m device at a drain bias of 20 V, it exhibits a maximum output power density (P-out) of 2.83 W/mm with a maximum 24.97% power-added efficiency (PAE). Additionally, for the 8 x 50 mu m device at a drain bias of 32V, it achieves a P-out of 1.27 W (3.18 W/mm). This work demonstrates that the novel gate fabrication process of shrinking gate head by using SiNx shield achieves high-frequency and high-output power characteristics for Ka-band application.

This paper introduces the deposition of seed layers using a soaking technique to deposit dielectric layers on transition metal dichalcogenides (TMDs). This method addresses the bottleneck caused by the lack of dangling bonds in two-dimensional materials, which hinders the adsorption of precursors during the ALD process. We utilize the Hafnium soak technique, which can facilitate depositing a gate dielectric onto TMDs exhibiting smooth film characteristics and outstanding physical properties. We fabricate dual-gate devices using TMDs with an equivalent oxide thickness (EOT) of 1 nm and a subthreshold swing (S.S.) of 94 mV/dec. Additionally, the soaking technique promotes growth on both the top and back sides of two-dimensional materials, facilitating the development of gate-all-around (GAA) field-effect transistors.

In this work, we investigate the RF performance degradations in AlGaN/GaN high-electron mobility transistors (HEMTs) subjected to high-temperature ON-state dc stress (VDS = 18 V, IDS = 300 mA/mm). The main focus was on the RF degradation mechanism analysis induced by merely dc stress for short gate-length devices targeting for millimeter-wave applications. Throughout the dc stress process, variations in device parameters were meticulously measured and extracted. It was noted that the device exhibited an increase in intrinsic gate capacitance and parasitic resistance, leading to the degradation in unit-current-gain cutoff frequency (fT) and maximum oscillation frequency (fMAX). Investigation of the degradation mechanism was first conducted through the current transient measurement methodology and then analyzed by TCAD simulation. It is concluded that the additional acceptor-like traps generated in the AlGaN barrier tend to increase the net charge density leading to the increase of total gate capacitance as well as the decrease in the transconductance, which causes the severe degradations in the RF performance after stress. This analysis offers deeper insights into the primary mechanisms behind RF performance degradation induced by dc stress in GaN HEMTs operating at millimeter-wave frequencies.

A K-/Ka-band high-power single-pole-double-throw (SPDT) switch featuring absorptive characteristic for mobile satellite communication (SATCOM) phased arrays is presented in this work. Conventionally, the operating bandwidth of the absorptive RF switches were limited due to the adoption of two quarter-wavelength transmission lines for the reflective and absorptive branch. Through theoretical analysis, a wideband absorptive SPDT switch was realized using the 0.12-mu m GaN/SiC high-electron mobility transistor (HEMT) technology. The experimental results have demonstrated an insertion loss of less than 3.2 dB, an isolation of greater than 26.2 dB, and an input 0.1-dB compression point (P(0.1)dB) of better than 32.6 dBm from the 17-30 GHz, respectively.

This paper introduces a dual-band dual circularly-polarized (DB-DCP) antenna configuration suitable for the simultaneous uplink and downlink (UL/DL) operation in satellite communication systems. The dual-band CP performance is realized by using a dual-band branch-line coupler (DB-BLC) with +/-90 o phase offsets between the split ports at the dual frequencies. Either the dual-band same CP (DB-SCP) or the dual-band opposite CP (DB-OCP) antennas can be implemented through the proper selection of the DB-BLC topology. The opposite polarization feature at the two bands of the DB-OCP antennas further enhances the isolation between the UL and DL bands through additional polarization diversity. The selection of operating modes is achievable by switching the excitation ports, providing great flexibility for system applications. The proposed configuration features the ease of fabrication using standard 2-layer printed circuit board (PCB) technology, and its planar structure makes it easy for integration with other circuitries at the system level. The proposed designs have been experimentally validated. The measurement results of the DB-SCP and DB-OCP antennas revealed an applicable system bandwidth (the intersection of impedance bandwidth and the axial ratio bandwidth) of 9.42%/6.40% and 8.06%/4.50% at 28 and 38 GHz, respectively, with reasonable antenna gain and total efficiency.

This paper presents a wideband antenna system for 5G smartphones, integrating a Dipole Antenna with a Substrate Integrated Waveguide (SIW). Integrating the Dipole antenna with SIW mitigates transition losses between the feed port and radiator, enhancing efficiency at the mm-wave frequency band. The SIW structure further suppresses surface waves, improving radiation efficiency while maintaining excellent pattern integrity. The antenna operates broadly from (24.2%) 28.4 to 36.2 GHz. The proposed orthogonal antenna topology accommodates real-world usage scenarios, allowing seamless operation in single- and dualhand modes. The compact design fits within modern 5 G smartphone panel constraints, precisely an 8 mm height, making it highly practical for integration. Additionally, the antenna achieves a mutual coupling lower than 11 dB. Attention to user safety is also prioritized, with radiation exposure to the user minimized upon integrating the antenna into the smartphone panel. This wideband operation, low mutual coupling, high pattern integrity, and user-centric design overcomes the challenges associated with 5G antenna systems, ensuring robust and reliable communication in compact smartphone platforms.

In this work, we present the design of a fully-integrated transceiver module for V-band wireless communication systems. A low-noise power amplifier (LNPA) and a reflective single-pole-double-throw switch were utilized as the building blocks of the proposed transceiver. The SPDT switch was designed and integrated with the discrete devices after a theoretical analysis of the packaging and matching network conditions. Integrated with the dual-exponentially tapered slot antenna fabricated on Rogers RO3010 substrate, the V-band transceiver has demonstrated a maximum equivalent isotropically radiated power of 30.5 dBm. The experimental results have shown great potential for the formation unit in V-band large-scale transceiver systems.

Scaling of GaN high-electron-mobility transistors (HEMTs) frequently leads to increased gate leakage current and increased risk of device breakdown when subjected to high-speed switching, ultimately resulting in a reduction of the maximum drain current and output power density. These issues can be effectively mitigated by incorporating a dielectric layer beneath the gate in HEMTs. This study delves into the performance enhancement of Hf0.5Zr0.5O2-gated InAlGaN/GaN metal–insulator–semiconductor (MIS) HEMTs that are grown on a ZrO2 seed layer. The implementation of ferroelectric Hf0.5Zr0.5O2(HZO) stacks has been shown to significantly reduce gate leakage current and stabilize threshold voltage shifts. Furthermore, the positive bias transconductance peak shift enhances the overall electrical stability of the device. Our findings underscore the potential of using ferroelectric stacks in InAlGaN/GaN HEMTs to achieve higher efficiency and operational stability. These advancements make Hf0.5Zr0.5O2-gated HEMTs particularly suitable for advanced high-power and high-frequency applications, demonstrating their capacity to deliver superior performance under challenging conditions. The results of this study highlight the critical role of dielectric engineering in optimizing GaN-based devices, paving the way for future innovations in semiconductor technology.

This paper introduces a novel technique for inducing circular polarization in a single radiator through the implementation of a sequentially rotated feeding network. Analogous to the operational principles of sequentially rotated antennas employing multiple radiators, the creation of circular polarization (CP) with a solitary radiator becomes achievable through the distinctive phase and angular arrangement facilitated by the feeding network. This innovative approach not only results in a substantial reduction in complexity but also contributes to an overall reduction in antenna size, all while upholding commendable CP performance in terms of both axial ratio (AR) bandwidth and beamwidth.

A highly linear power amplifier (PA) utilizing stacked-FET configuration and harmonic-tuning technique targeting for millimeter-wave applications is presented in this work. Fabricated using standard 150-nm GaN/SiC device technology, a small-signal gain of 23.7 dB, a peak power-added-efficiency (PAE) of 37.7%, and a saturated output power (P sat ) of 30.8 dBm was evaluated with continuous-wave (CW) excitation at 38 GHz, respectively. With the characterization using a standard 200 MHz 64-quadrature-amplitude-modulation (QAM) 5G new-ratio (NR) signal, the fabricated PA exhibited an error-vector-magnitude (EVM) of -27.9 dB with an average PAE of 21.4% while delivering an average output power of 25.1 dBm at 38 GHz. The experimental results have evidenced that the design technique is capable of achieving wide harmonic-tuning range for millimeter-wave amplifiers requiring high linearity and enhancement in overall efficiency.

A 4-port MIMO antenna, featuring transparency and flexibility with a low profile of 0.47 lambda x0.58 lambda x0.010 lambda (at 3.19 GHz) is proposed. Transparency and flexibility of the antenna are achieved by utilizing materials like PET and silver oxide. The fundamental antenna comprises a semi-hollow circular structure with notches on the upper side and a lower side consisting of a partial ground to attain an ultrawideband response. To enable MIMO capability, four identical elements are strategically positioned in a sequential rotational arrangement, effectively realizing the diversity performance. A centrally positioned circular slotted structure, linked by vertical lines, establishes the ground connection between the elements. By upholding a shared reference, the isolation surpasses 20 dB. The antenna exhibits a peak gain of 2.49 dBi and maintains an efficiency greater than 40%. It also achieves an impressive 10-dB impedance bandwidth (IBW) spanning (97.83%) from 3.19 to 9.30 GHz, while maintaining an envelope correlation coefficient (ECC) of under 0.1. The decent results of S-parameters and ECC assessments under bending conditions, as well as a comprehensive time-domain analysis, all of which underscore its outstanding performance. The UWB flexible transparent MIMO antenna fulfills crucial criteria for IoT applications, offering high data rates, spectrum efficiency, adaptability, and easy integration. This technology holds significant promise for the rapidly growing IoT ecosystem.

This paper presents two different configurations of +/- 45 degrees dual-wideband dual-polarized (DWDP) antennas. The antenna comprises eight end-loaded broadband dipoles grouped into two sets based on the bands of operation. The high-frequency dipoles are strategically placed within the low-frequency ones to form the elementary unit. Further optimization has been performed on the elementary unit in terms of the radiator placement to suppress sidelobe levels for array formation. Both configurations are meticulously fabricated using an all-metal structure, demonstrating durability and the simplicity of fabrication. The antenna designs achieve +/- 45 degrees polarization, high gain, satisfactory cross-polarization discrimination (XPD), and wide impedance bandwidth covering 0.67-1.04 GHz and 1.54-3 GHz bands. Despite the nested configuration, mutual coupling is well within acceptable limits. Formation of the array based on the optimum elementary unit has been investigated by simulation, revealing reasonable gain enhancement and low sidelobe levels across all bands. This comprehensive approach yields a robust, high-performing antenna configuration suitable for indoor distributed antenna system (IDAS) applications. Two innovative configurations of dual-polarized antennas, utilizing strategically grouped broadband dipoles for high gain and wide impedance bandwidth. Through meticulous optimization of the elementary unit, the paper achieves low sidelobe levels and reasonable gain enhancement in array formation, enhancing the overall performance of the antennas. The antennas are robustly fabricated using an all-metal structure, ensuring durability and simplicity in fabrication. This, combined with satisfactory cross-polarization discrimination and mutual coupling, positions the proposed antennas as high-performing solutions suitable for IDAS applications. image

In this study, AlGaN/GaN high-electron-mobility-transistor (HEMT) with thick Cu metallization is investigated, and the Radio Frequency (RF) performance and the reliability are analyzed. By applying thick Cu metallization of 6.0 mu m as interconnect, the cut-off frequency (f(T)), the maximum oscillation frequency (f(max)), and the power performance can be improved. Besides, the thick-Cu-metallized device exhibits reduced minimum noise figure (NFmin) of 0.7, 1.0, 2.2 and 2.8 dB at 12, 14, 28 and 38 GHz, respectively, which can be attributed to the reduction of the source and drain resistance caused by thick Cu metallization. Furthermore, for stress test under high drain-to-source voltage (V-DS) and high temperature, the proposed device exhibits good stability. The results show that the thick Cu metallization technology has great potential to be applied in satellite communication system.

RF switch is an essential component for phased- array antennas in modern communication systems. The series-shunt configuration is preferable due to the balanced performance of high isolation and power handling capability. Conventionally, such configuration suffered from phase fluctuations over the input power drive making extra phase compensation necessary for proper system operation. Theoretical analysis by an equivalent circuit model revealed that the phase fluctuation was primarily caused by the capacitance of the devices in the series arm. We thus proposed a design using the single-pole-double-throw (SPDT) configuration as an example featuring minimum phase variation over a very wide RF input power range. Compared to the conventional one, the proposed design achieved at least a reduction of over 10 degrees at 28 GHz in phase variation over a wide input power range up to the input 1-dB compression point (P-1 dB). To our knowledge, this is the first series-shunt type SPDT switch study achieving the minimum phase variation over wide input power levels.

This book presents design procedure & modeling of novel antenna geometries for Sub-6 GHz 5G wireless applications & communication systems.

This work introduces a scalable transceiver module consisting of 64-element circularly polarized (CP) antenna array, employing GaN technology. The antenna array is configured orthogonally to achieve CP and mitigate cross-polarization effects. Utilizing a high-power, linear power amplifier (PA) implemented in 0.15-mu m GaN high-electron mobility transistor (HEMT) technology, the module achieves a saturated equivalent isotropically radiated power (EIRP) of 65 dBm with only 64 elements operating in the frequency range of 17-21 GHz. This configuration optimizes the module's dimensions, promoting scalability for diverse applications with stringent EIRP requirements, particularly suitable for CubeSat applications.

A novel optically transparent Multi Input Multi Output (MIMO) antenna design positioned on a Frequency-Selective Surface (FSS) for gain improvement while maintaining a simple fabrication procedure. Transparent conductive materials inherently exhibit higher sheet impedance due to lower conductivity, resulting in decreased antenna gain and radiation efficiency. To address this limitation, an optically transparent FSS is incorporated beneath the MIMO structure to improve radiation characteristics. Utilizing a Malinex substrate and a conductive silver oxide sheet, the 4-element MIMO design achieves both transparency and MIMO operability. The operational bandwidth spans from 3.09GHz to 3.7GHz, with a percentage bandwidth of 17.96%, ensuring port isolation of over 20dB. With the presence of the FSS, a consistent gain enhancement of approximately 3.46 dBi is achieved, with an average gain within the band reaching 4.56 dBi. The proposed design employs a simplified fabrication process while addressing aesthetic concerns and providing a solution to the existing issue of low gain in conductive metal oxide-based transparent antennas.