This paper presents a theoretical analysis of the load modulation conditions in a Load Modulated Balanced Amplifier architecture as a function of the type of hybrid coupler employed. In particular, two cases are examined: the $\mathbf{9 0}$-degree hybrid coupler and the $\mathbf{1 8 0}$-degree hybrid coupler. Furthermore, the feasibility of controlling the load impedance at higher harmonic frequencies is also investigated.

This contribution presents a $5-\mathrm{V} 1.8-\mathrm{W}$ GaAs HBT Doherty power amplifier MMIC conceived for Wi-Fi 6E applications in the $6-7 \text{GHz}$ band. The paper discusses the solutions adopted, at transistor and amplifier level, to deal with the challenges posed by the demanding design frequency, which is at the limit of the commercially available technologies. The proposed amplifier achieves more than 23% efficiency in a 5-dB back-off range, as well as good linearity performance when tested with wideband Wi-Fi 6E modulated signals.

This research focuses on the design and simulation of a V-band single-chip transmit-and-receive front-end integrating an LNA, PA and switching functions for ISL terminals. Two technologies are compared: a 60 nm GaN/Si HEMT from MESC and a 100 nm GaAs HEMT from UMS. In Tx mode, the proposed design targets a saturated output power of at least 20 dBm and a power-added efficiency of no less than 5%. In Rx mode, the goal is 4 dB noise figure. In both cases, the small signal gain must exceed 20 dB across the 59-71 GHz band.

This paper presents a series-parallel RF power amplifier (PA) configuration with improved linearity performance achieved through an optimal combination of gate bias voltages and input power levels. The fundamental output voltage and the total third-order intermodulation distortion (IMD3) expressions of the series-parallel PA are analytically derived. Moreover, the proposed algorithm systematically determines optimal gate bias combinations for driver and power stages through comprehensive device characterization, harmonic balance simulations, and vector-based IMD3 cancellation analysis to maximize the achievable performance in terms of both linearity and efficiency. In addition, the fundamental and harmonic transconductances for different transistor active areas have been analyzed. This analysis determines the suitable number of gate fingers N-f and gate width W-f of the transistor in both driver and final stages to fulfill the required output power level, considering linearity and efficiency performance requirements. A 2-W X-band high linear and efficient RF PA is designed and fabricated in a 0.15-mu m GaN-on-SiC process. A good agreement between simulations and measurements has been achieved. The continuous wave measurements of the proposed PA showed a power gain of 19 dB, a saturated output power level of more than 34-dBm, together with a power added efficiency (PAE) of 40% at 1-dB compression point. The two-tone signal measurements showed a similar gain level with a PAE of more than 37% at 33.5-dBm of output power. Moreover, the IMD3 is below-30-dBc while the PAE is greater than 33%. Modulated measurements using a 5-MHz WCDMA signal (PAPR = 3.5 dB) confirmed the PA linearity improvement perfomance, showing an adjacent channel power ratio (ACPR) of-27 dBc and an error vector magnitude (EVM) between 1.9 and 5.1% across its output power range, making it suitable for high-order modulation schemes. The results validate the proposed design approach, offering competitive performance with respect to the actual state of the art 6G communication systems by balancing efficiency, linearity, and reliability.

This contribution presents the development and the experimental results of a spaceborne VHF high-power Solid-State Power Amplifier (SSPA) based on European Gallium Nitride technology, suitable for integration in future Earth observation subsurface radar instrument. The developed high-power section of the overall SSPA delivers an output power exceeding 800 W with an associated gain and power added efficiency of about 21 dB and 70 %, respectively, from 40 to 50 MHz.

Understanding the frequency-dependent transistor performance is essential to making the best use of this component for the purpose of designing an effective microwave circuit. This work is prompted by this point and focuses on the analysis of the kink effect occurring in the output reflection coefficient ($S_{22}$) of microwave transistors. A systematic method based on the complex Lorentzian function is developed to straightforwardly fit the frequency-dependent behaviour of $S_{22}$ and, in turn, to effectively determine a set of parameters for an accurate and complete characterization of the kink effect. To validate the proposed methodology, the gallium-nitride high-electron-mobility transistors (GaN HEMT) technology is taken into consideration as a case study. Investigating the frequency-dependent behavior of GaN HEMTs is especially critical for aerospace radar and communication applications. A complete and accurate device characterization across a wide frequency range is crucial to achieving reliable high-frequency performance in such complex and demanding systems.

This article presents the design and experimental characterization of an engineering model (EM) solid-state power amplifier (SSPA) based on European 0.5- $\mu $ m gallium nitride (GaN) on silicon carbide technology, conceived for next-generation flexible L-band navigation payloads. Operating in the E1 band ( $1575.42\pm 25$ MHz), the unit integrates a radio frequency tray (RFT) to amplify the useful signal, and an electronic power conditioner (EPC), which provides telecommand/telemetry functions, remote mode selection, and interfaces the module with the satellite primary bus. Continuous-wave measurements demonstrate an adjustable output power range from 50.8 to 54.8 dBm with efficiency above 41%, including EPC consumption and connector/isolator losses. The amplifier also exhibits excellent thermal stability, with output power variation below 0.1 dB across -20 degrees C to +65 degrees C temperature range. Under Galileo-like modulated signals, it ensures full compliance with the spectral emission masks, thanks to an embedded analog linearizer (LIN), while delivering up to 300-W average output power with efficiencies up to 48%. The SSPA is multipaction free and fulfills all the space derating rules in terms of junction temperature and voltage/current swings for the involved GaN active devices. Compared with previously reported GaN SSPAs, the proposed design uniquely combines embedded output power flexibility and analog linearization in a compact, lightweight, space-ready unit. In particular, its power flexibility enables a reduction of more than 130 W in dc power consumption in low-power mode, easing thermal management and enhancing reliability, thus offering a valid solution for implementing high-reliability next-generation reconfigurable satellite payloads entirely based on solid-state technology.

This paper presents a novel design strategy to enhance the performance of a Doherty Power Amplifier using a nonlinear driver stage in the Peaking branch. To implement a class F harmonic termination for the peaking final stage, a third harmonic voltage component is injected at the input by a driver stage, allowing the phase of the third harmonic current at the output of the final stage to be reversed compared to its normal evolution. This enables a class F design strategy for a class C biased device. The paper details the theoretical foundation of the proposed approach together with a thoroughly experimental verification of its applicability at both device and circuit level. The prototype for X-Band applications is implemented on the 120 nm gate-length GaN-on-SiC technology from WIN Semiconductors. The MMIC delivers over 36 dBm of output power and 40% efficiency at 10 GHz. Additionally, when tested with modulated signals having 10 MHz channel bandwidth and 6 dB Peak-to-Average Power Ratio, the linearity threshold of Adjacent Channel Power Ratio of - 30 dBc is achieved with an average output power exceeding 32 dBm and efficiency greater than 32%.

In this paper, we propose a new measurement setup for the characterization of microwave power bars up to 150 W. By operating at low-frequency (i.e., a few megahertz), it overcomes the limitations of microwave systems and enables the characterization of the power-bar resistive behavior under conditions consistent with high-frequency operation. Such a kind of characterization provides data that can be directly used to enhance nonlinear model accuracy by overcoming the limitations of state-of-the-art power-bar models obtained by simply scaling the behavior of the unit-cell device. In fact, thermal and trapoccupation states, as well as distributed (passive) access structures to the device active area, do not scale with the periphery in powerbar devices. The setup has been fully validated by characterizing a 130-W GaN power bar under class-E operation. Measurement results have then been used for the design of a VHF power amplifier.

This contribution presents a 3.5W MMIC power amplifier in GaAs HBT technology operating at 5 V supply conceived for Wi-Fi 6 applications in the 5-6 GHz frequency range. A 3-stage corporate architecture is selected to evaluate the technology capability in terms of power, linearity and efficiency. In simulation, the designed amplifier shows a saturated output power in excess of 35 dBm with associated gain and efficiency above 27 dB and 36 %, respectively. At -26 dB of EVM (Error Vector Magnitude, MCS0 standard) the best efficiency achievable, with simple bias tuning, is 17 % with an associated output power of 29 dBm. The small-signal characterization shows a very good agreement between measurements and simulations.

This work establishes a methodology based on continuous-wave load-pull data in order to estimate modulated figures of merit for radio-frequency transistors. By automatically accounting for source termination effects without any measurement overhead, the technique allows to fully explore the intrinsic trade-offs between linearity, gain, output power and power added efficiency. The approach is used to experimentally analyze three different layouts of gallium arsenide (GaAs) Heterojunction Bipolar Transistor (HBT) power cells for Wi-Fi 6 applications.

In this paper, the design of a hybrid power amplifier (PA) in the very high frequency (VHF) band for satellite remote sensing applications is discussed. A Class $\mathbf{F}^{-\mathbf{1}}$ design strategy was adopted to maximize the efficiency performance of the space-evaluated CHKA012bSYA GaN packaged device from United Monolithic Semiconductors. The proper shaping of voltage and current waveforms across the device terminals was achieved by careful design of the output matching network using resonating L-C filters. A 75% de-rating was applied in the design process to ensure compliance with space reliability requirements. The proposed PA provides an output power exceeding 100 W with a power added efficiency and a gain of about 80% and 25 dB, respectively, within 40−50 MHz.

In this paper, a characterization procedure for III-V compound semiconductor technology is proposed, with the aim of investigating the performance of state-of-the-art transistors for mm-wave applications. The whole procedure has been successfully applied to a 0.1-mu m GaAs pHEMT process, which was characterized under DC, small- and large-signal operations, after a first stress experiment necessary to assess its robustness and stability.

This paper presents an integrated three-stage Doherty power amplifier for Wi-Fi 6 applications operating in the $5-6.2 \text{GHz}$ frequency range. The H20U-C4 GaAs HBT technology available at WIN semiconductors is chosen for its excellent linearity and good efficiency features. The power cells adopted as active devices are designed to be thermally and RF stable through the proper selection of ballast resistors and capacitors. A comprehensive measurement campaign was conducted, demonstrating an output power, efficiency and gain larger than $32 \text{dBm}, 35 \%$ and 22.5 dB, respectively, at saturation. At 6 dB of output back-off the efficiency is better than 20% all over the specified bandwidth. Moreover, when tested with a 20 MHz MCS11 signal having 10 dB PAPR, the DPA provides an average output power of 22 dBm with an efficiency and EVM of 11% and −25 dB, respectively.

This paper presents the design and the experimental results of a C-Band Monolithic Microwave Integrated Circuit (MMIC) High Power Amplifier (HPA) based on a commercially available $\mathbf{0.25}\ \boldsymbol{\mu} \mathbf{m}$ GaN-on-SiC technology and conceived for broadband Radar systems front-end integration. The HPA is based on a two-stage corporate topology and provides an output power higher than 22 W, with a power added efficiency and an associated gain greater than 40% and 24 dB, respectively, from 4 GHz to 5.2GHz. Furthermore, small signal measurements show significant input and output return losses better than −12 dB and −15 dB. The compact overall chip area is $\mathbf{5}\times \mathbf{4.8}\ \mathbf{mm}^{\mathbf{2}}$ .

The design, realization, and test of a Ka-band gallium nitride (GaN) monolithic microwave-integrated circuit (MMIC) single-chip front-end (SCFE) is presented. The MMIC, realized in OMMIC's 100- and 60-nm gate length GaN on Silicon process, integrates high-power and low-noise amplification together with transmit or receive selection switches in a 4.7 x 3.0 mm chip area. The SCFE is conceived for active electronically scanned antenna applications operating from 32 to 36 GHz. In RX mode, a typical noise figure of 3.2 dB and gain better than 3B have been measured. In TX mode, the typical output power and the power-added efficiency (PAE) are 35 dBm and 16%, respectively. A drain bias point trade-off analysis is performed so the power amplifier's transistors channel temperature remains below 160. while design charts are provided for the synthesis of the low-noise amplifier (LNA) block. Finally, 100- and 60-nm gate length transistors are combined on the MMIC to improve its performance in terms of receive noise figure and transmit gain and output power. To the best of the authors' knowledge, this GaN SCFE features the highest operating frequency reported in the open literature regarding integrated GaN/Si solutions and compares well with GaN/SiC MMICs especially considering the CW test condition here reported while concurrently fulfilling the FET's channel temperature requirement.

The goal of the present work is to study the influence of the thermal effects on the small- and large-signal characteristics of gallium nitride (GaN) high-electron-mobility transistor (HEMT) devices by using an extensive campaign of measurements. The studied devices were manufactured using a 0.15 mu m process on silicon carbide (SiC) substrate. Experiments carried out on the three HEMTs with different gate widths are investigated in detail to get a thorough comprehension of how changing the backside temperature up to 100 degrees C affects the transistor performance.

This letter presents the design of a Doherty power amplifier (DPA) for satellite applications in the $Ka$ -band downlink (17.3–20.3 GHz) implemented on a 100-nm GaN–Si HEMT technology. The design aims to achieve high gain and very high intrinsic linearity over a wide bandwidth of 3 GHz. The experimental characterization on the fabricated chip demonstrates that the DPA can maintain a noise-to-power ratio (NPR) higher than 25 dB and power-added efficiency (PAE) of 30% while providing 36 dBm of output power, when tested with a 100-MHz uniformly distributed signal, achieving state-of-the-art performance among the integrated power amplifiers for satellite communications.

The dynamic behaviour of RF power splitters has great impact in the behavior of dual-branch RF power amplifiers (PAs) such as Doherty power amplifiers (DPAs). Recently, we have introduced a structure as a nonlinear power splitter which has the capability to change the power ratio based on the terminal impedances in the output ports. In the previous work, we discussed the amplitude response of this new structure and how we can deliver more power to one branch or vice versa in dual branch configurations. But, for using this structure in the Doherty amplifier, the phase response of this structure is crucial as well In this paper, we analyze the phase response of the standard Hybrid Branch Line Coupler (HBLC) structure and then we show that the phase response of the nonlinear power splitter has some advantages that make it easier to use in the Doherty power amplifier design. Continuing, we show some potential applications of the nonlinear power splitters for RF/Microwave amplifications.