This paper presents a novel power combining architecture, referred to as distributed efficient power amplifier (DEPA) that mitigates the inherent bandwidth limiting factors in a Doherty power amplifier (DPA), namely, impedance inversion and load modulation, by distributing the conventional auxiliary amplifier of the DPA to multiple auxiliary subamplifiers along a broadband multisection impedance transformer. The proposed technique is demonstrated through the design, implementation, and measurement of a wideband DEPA having 8-dB output power back-off and 72% fractional bandwidth. The experimental results show a Doherty-like efficiency enhancement from 1.8 to 3.8 GHz. For the output power levels of 37.4±1.1 and 45.4±1.1 dBm, corresponding to 8-dB OBO and peak output power, the efficiency levels are between 41%-51% and 42%-62%, respectively. Furthermore, linearized modulated measurements show that the DEPA is linearizable and meets the spectral requirements for modern wireless communication systems.

This article presents a technique for load-modulated balanced amplifiers (LMBAs) to achieve a continuum of load modulation (LM) ratio. This has been possible in prior arts using asymmetrical auxiliary devices. In contrast, the proposed technique employs identical auxiliary devices. A LM ratio is enabled by a specific coupling factor of the power-combining coupler at the output. The proposed LMBA technique is demonstrated through the design, implementation, and measurement of a concurrent wideband LMBA operating across 3.1-4.2 GHz. The prototype achieves a peak output power of 48.1±0.6dBm, with drain efficiency of 47-58% at peak power and 47-61% at 10-dB power back-off. The concurrent wideband performance is demonstrated by a characterization with 900-MHz new radio (NR) signal with 10-dB peak-to-average power ratio (PAPR). At 37.8 dBm of average output power, the measurement yields 44% drain efficiency and -44-dBc adjacent channel leakage ratio (ACLR).

A 24-28-GHz two-stage GaN Doherty power amplifier (PA) is designed and characterized. At millimeter-wave (mm-wave) frequencies, the low output impedance of the auxiliary transistor loads the Doherty combining network, which lowers the power added efficiency (PAE) in back-off. In this design, a small periphery auxiliary transistor is used to increase the output impedance of the auxiliary transistor. The periphery ratio of the auxiliary and the main transistors is 77%. Even though, compared to symmetric Doherty PAs, the load modulation of the main transistor is reduced, this amplifier still achieves 32% and 23% PAE at 6 and 9-dB output power back-off, respectively. Attributing to the small auxiliary transistor, the amplifier obtains a small signal gain of 19 dB. The maximum output power of the amplifier is 4 W with a peak PAE of 42%.

This article proposes a unified theory on power combining with a continuum of load modulation (LM) ratios. Two well-known power amplifier (PA) techniques, Doherty and traveling-wave amplifiers, are the two extreme examples within this continuum, yielding full and zero LMs, respectively. Based on this theory, a power-combining technique is proposed, which optimizes efficiency and bandwidth at a certain power backoff (BO) level, which is often in between the two well-known architectures. As a demonstration, a PA with an LM ratio of $1.4$ is designed. It achieves a peak output power of In49.3±0.5 dBm and 47%-60% drain efficiency at 8-dB power BO over 2.6-3.8 GHz. The linearizability and practical usefulness of this PA are demonstrated through linearized-modulated measurements.

This work proposes an improved technique for accurate, contactless measurement of the absolute voltage waveforms of microwave circuits, employing a passive electric-field sensing probe. The proposed technique uses an electromagnetic model of the interaction between the probe and a device under test, to allow the extraction of the coupling capacitance variation versus frequency. Employing these information the measurement accuracy is improved, especially for higher (i.e., harmonic) frequencies, yielding enhanced waveform fidelity. The proposed method is validated on a microstrip line carrying waveforms with rich harmonic content. The accuracy of the proposed technique is benchmarked against a conventional thru-reflect-line (TRL) de-embedding approach by a nonlinear vector network analyzer (NVNA). Measurement results show that the root-mean square (RMS) error can be improved by 3 percentage points (from 8% to 5%) compared to the prior arts over the frequency range from 1 to 5 GHz.

Conventional multiband power amplifiers (PAs), when working in time-division duplex (TDD), require the transmit–receive intervals of all bands to be synchronized. This is an undesirable constraint in modern radio base stations. This article proposes a dual-output dual-band Doherty PA (DB-DPA) that enables the loading of one band to be switched on-and-off without impacting the other band in normal transmission. A thorough analysis of the proposed dual-output DB-DPA architecture is presented, and a dual-output DB-DPA prototype operating at 1.4 and 2.6GHz has been designed as a proof of concept. The large-signal measurements of the prototype DB-DPA indicate Doherty behavior at both frequencies with over 56% saturation efficiency and 45% efficiency at 6-dB power back-off (PBO). Furthermore, single-band and concurrent dual-band linearized modulated measurements, using 10-MHz new radio (NR) signals with 6-dB peak-to-average power ratio (PAPR), demonstrate the linearizability of the proposed DB-DPA and its usefulness for unsynchronized TDD applications.