Microwave Measurements Part I: Linear Measurements

An Overview of the most relevant issues concerning RF and microwave linear measurements is presented. Vector Network Analyzer foremost used instrumentation for this kind of measures is describe

Microwave Measurements. Part II - Nonlinear Measurements

This paper addresses the problems in microwave non-linear measurements. It discusses techniques to synthesize loads, the most used non-linear measurement techniques, and harmonic load-pulling. An experimental setup for characterizing power amplifiers must be able to measure the complex spectrum of the waves at the amplifier ports as a function of frequency, input power, and source and load termination at the fundamental and harmonic frequencies. The vector network analyzer (VNA) is the core instrument used in the non-linear characterization scenario. The basic idea is to keep the operations of VNA/mixers linear, diverting to them only a small portion of the signal present at the device under test (DUT) ports, therefore keeping unaltered the VNA capabilities already exhibited for small signal measurements

Efficiency versus linearity trade-off in an S-band class-AB power amplifier

This paper presents a design strategy to simultaneously optimize the efficiency and linearity of a single-device class-AB power amplifier, given minimum output power and gain requirements. The adopted linearity metric is the highest inter-modulation distortion in a two-tone test with 20MHz spacing. The simultaneous selection of optimum source and load terminations that provide the best trade-off among all of the requirements is described in detail, and the synthesis of the matching networks is then presented. A prototype is developed based on a 6W packaged GaN device around 3.5 GHz, manufactured and measured. According to the measured results, the amplifier achieves output power higher than 38dBm with associated gain higher than 12 dB and saturated power-added efficiency in excess of 73% in a single-tone test at 3.25 GHz, while providing a 33% power-added efficiency and -30 dBc inter-modulation distortion in the 20MHz two-tone test

Ka-band MMIC GaN Doherty Power Amplifiers: Considerations on Technologies and Architectures

This paper presents a comparison of two sample GaN technologies, one on Silicon and the other on Silicon Carbide substrate, when applied to the design of an integrated Doherty power amplifier. Two different target applications are considered, namely the satellite Ka-band downlink (17.3-20.3 GHz) and terrestrial communications in the n257 FR2 5G band (26.5-29.5 GHz), with different specifications but similar absolute frequency ranges. Considerations are made highlighting the advantages and disadvantages of the two technologies for the design of high-frequency MMIC Doherty Power Amplifiers in the presented scenarios

When self-consistency makes a difference

Compound semiconductor power RF and microwave device modeling requires, in many cases, the use of selfconsistent electrothermal equivalent circuits. The slow thermal dynamics and the thermal nonlinearity should be accurately included in the model; otherwise, some response features subtly related to the detailed frequency behavior of the slow thermal dynamics would be inaccurately reproduced or completely distorted. In this contribution we show two examples, concerning current collapse in HBTs and modeling of IMPs in GaN HEMTs. Accurate thermal modeling is proved to be be made compatible with circuit-oriented CAD tools through a proper choice of system-level approximations; in the discussion we exploit a Wiener approach, but of course the strategy should be tailored to the specific problem under consideratio

Watt-Level Ka-Band Integrated Doherty Power Amplifiers: Technologies and Power Combination Strategies Invited Paper

This paper discusses some of the design choices underlying the development of watt-level integrated Doherty power amplifiers in the K and Ka band, focusing on compound semiconductor technologies. The key aspect of on-chip power combination is discussed, presenting and comparing some of the possible alternatives. Then, the impact on the achievable bandwidth and performance of different parameters is quantified, adopting an approximate analysis, which focuses on the Doherty output combiner and allows estimating the non-linear performance of the amplifier thanks to some simplifying assumptions, without requiring a full, non-linear model of the active devices. Two sample GaAs and GaN technologies are compared first, considering parameters that are representative of the currently available commercial processes, and then several power combination strategies are analyzed, adopting the GaN technology, which is currently the only one that allows achieving the power levels required by the applications directly on chip. Finally, some hints as to the impact of the output parasitic effects of the transistors on the presented analysis are given

Behavioral modeling of GaN-based power amplifiers: impact of electrothermal feedback on the model accuracy and identification

In this article, we discuss the accuracy of behavioral models in simulating the intermodulation distortion (IMD) of microwave GaN-based high-power amplifiers in the presence of strong electrothermal (ET) feedback. Exploiting an accurate self-consistent ET model derived from measurements and thermal finite-element method simulations, we show that behavioral models are able to yield accurate results, provided that the model identification is carried out with signals with wide bandwidth and large dynamics

Assessment of the Performance of Inverse Class-F Power Amplifiers in a Discrete Doherty Architecture

This work presents an assessment, at simulation and experimental levels, of the performance of inverse class-F power amplifiers in a Doherty architecture. Two connectorized amplifier modules, designed for standalone operation, are adopted to construct a quasi-balanced Doherty architecture exploiting 3-dB 90° hybrid couplers at the input and output to demonstrate the concept. The Doherty architecture shows competitive performance at 1.8 GHz, with 43 dBm output power and around 60% efficiency from saturation to 6 dB output power back-off. The performance is in line with the state of the art of integrated load-modulated amplifiers, demonstrating the validity of the approach

Evolution of Monolithic Technology for Wireless Communications: GaN MMIC Power Amplifiers For Microwave Radios

This paper presents the progress of monolithic technology for microwaveapplication, focusing on gallium nitride technology advances in the realization of integratedpower amplifiers. Three design examples, developed for microwave backhaul radios, areshown. The first design is a 7 GHz Doherty developed with a research foundry, while thesecond and the third are a 7 GHz Doherty and a 7–15 GHz dual-band combined poweramplifiers, both based on a commercial foundry process. The employed architectures, themain design steps and the pros and cons of using gallium nitride technology are highlighted.The measured performance demonstrates the potentialities of the employed technology, andthe progress in the accuracy, reliability and performance of the process

Continuous Inverse Class-F GaN Power Amplifier with 70% Efficiency over 1.4-2 GHz Bandwidth

This work presents the design and experimental characterization of a wideband continuous inverse class-F power amplifier, covering several bands in the 5G FR1 frequency range, and thus suitable for base station applications. The design spaces of the class-F and inverse class-F in terms of input and output terminations are reviewed and compared, and the design choices relative to an implementation using a packaged device are described. Measurements show a saturated output power of 40 dBm, with corresponding efficiency and gain higher than 70% and 13 dB, respectively, over 1.4-2 GHz. The performance is well in line with the state of the art and is accurately predicted by simulations, proving the effectiveness of the design strategy