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This paper presents an in-depth investigation of both isolated and non-isolated outphasing power amplifiers, with and without supply modulation. X-band GaN MMIC power amplifiers with 70% power-added efficiency and 2.7 W output power at 10.1 GHz are configured in hybrid outphasing circuits with several combiners that include bi-directional couplers, enabling calibrated measurements of internal load modulation. It is experimentally demonstrated that the load modulation critically depends on the power balance of the two internal MMIC PAs. Despite the additional loss in the combiner, peak total efficiencies greater than 47% are achieved by full outphasing PAs with more than 3.7 W of output power. A comparison between several outphasing configurations quantifies the improvement in efficiency for both isolated and non-isolated outphasing PAs with supply modulation.

This paper presents a theoretical analysis of harmonically terminated high-efficiency power rectifiers and experimental validation on a class-C single Schottky-diode rectifier and a class- F-1 GaN transistor rectifier. The theory is based on a Fourier analysis of current and voltage waveforms, which arise across the rectifying element when different harmonic terminations are presented at its terminals. An analogy to harmonically terminated power amplifier (PA) theory is discussed. From the analysis, one can obtain an optimal value for the dc load given the RF circuit design. An upper limit on rectifier efficiency is derived for each case as a function of the device on-resistance. Measured results from fundamental frequency source-pull measurement of a Schottky diode rectifier with short-circuit terminations at the second and third harmonics are presented. A maximal device rectification efficiency of 72.8% at 2.45 GHz matches the theoretical prediction. A 2.14-GHz GaN HEMT rectifier is designed based on a class-F-1 PA. The gate of the transistor is terminated in an optimal impedance for self-synchronous rectification. Measurements of conversion efficiency and output dc voltage for varying gate RF impedance, dc load, and gate bias are shown with varying input RF power at the drain. The rectifier demonstrates an efficiency of 85% for a 10-W input RF power at the transistor drain with a dc voltage of 30 V across a 98-Ω resistor.

International audience; This paper describes a novel fully calibrated four channel broadband time-domain measurement system for the characterization of nonlinear microwave devices with memory. The hardware architecture of the proposed time-domain measurement system is based on a wideband sub-sampling principle. The sampling heads work at a high strobe signal repetition frequency that can be tuned between 357-536 MHz. We achieve a 40-GHz RF frequency bandwidth and a 160-MHz IF bandwidth. This instrument enables the measurement of carrier and envelope waveforms at both ports of nonlinear microwave devices driven by broadband modulated multicarriers. The test-bench is applied to the cross modulation characterization of a 15-W GaN HEMT CREE S-band power amplifier with memory due to different biasing circuit configurations. The amplifier under test is driven by the sum of a large-signal modulated carrier (double-sideband amplitude modulation at 3.6 GHz) and a small single-tone signal at a 110-MHz offset frequency. Our significant contribution comes from the capability of the measurement system to record the time-domain waveforms of several nonadjacent modulated signals on a similar time equivalent scale for different cases of memory effects of the power amplifier under test.

International audience; This paper presents a calibrated measurement technique that enables phase and magnitude measurements of wideband multisines. This study is based on the use of a large-signal network analyzer (LSNA) performing harmonic sub-sampling and a fine frequency grid (20 MHz) comb generator calibrated using a high-frequency 50-GHz equivalent-time sampling scope. This comb generator is used as a harmonic phase reference generator for the calibration of the LSNA. The research reported here is applied to L-band multisine measurements, but it can be extended to higher microwave frequencies. The motivation of this study is to measure the multipactor phenomena effect in output RF multiplexers of satellite payloads.

A large-signal electrothermal model for AlGaN/GaN HEMTs including gate and drain related trapping effects is proposed here. This nonlinear model is well formulated to preserve convergence capabilities and simulation times. Extensive measurements have demonstrated the impact of trapping effects on the shapes of I(V) characteristics, as well as load cycles. It is shown that accurate modeling of gate-and drain-lag effects dramatically improves the large-signal simulation results. This is particularly true when the output loads deviate from the optimum matching conditions corresponding to real-world simulations. This new model and its modeling approach are presented here. Large-signal simulation results are then reported and compared to load-pull and large-signal network analyzer measurements for several load impedances at high voltage standing wave ratio and at two frequencies.