A miniaturized 2.4 GHz re-entrant cavity has been designed, manufactured and tested as a sensor for microfluidic compositional analysis. It has been fully evaluated experimentally with water and common solvents, namely methanol, ethanol, and chloroform, with excellent agreement with the expected behaviour predicted by the Debye model. The sensor’s performance has also been assessed for analysis of segmented flow using water and oil. The samples’ interaction with the electric field in the gap region has been maximized by aligning the sample tube parallel to the electric field in this region, and the small width of the gap (typically 1 mm) result in a highly localised complex permittivity measurement. The re-entrant cavity has simple mechanical geometry, small size, high quality factor, and due to the high concentration of electric field in the gap region, a very small mode volume. These factors combine to result in a highly sensitive, compact sensor for both pure liquids and liquid mixtures in capillary or microfluidic environments.

Many countries have allocated new frequency bands for fifth generation (5G) communication systems. In this paper, a wideband continuous class-F (CCF) radio frequency power amplifier (RFPA) is presented for the new 5G frequency band, from 3.3 GHz to 4.3 GHz using a 10 W Cree CGH40100F device. A unique wideband RFPA design approach for the output matching network (OMN) is also presented by applying a harmonic tuning network (HTN) for the harmonics and a low pass matching technique (LPMT) for the fundamental frequency. The RFPA is fabricated, and promising measurement results show a drain efficiency of 55.9% to 65.3% is achieved at an output power of 40 dBm (± 0.3 dBm) over a frequency range of 3.3 GHz to 4.3 GHz. A two-tone signal with a 10 MHz spacing was also applied to investigate the linearity of the RFPA.

The effects of the nonlinear drain-to-source capacitance (CDS), or the varactor effect, on the operation of continuous-mode class-B/J power amplifiers (PAs) are described in terms of the mathematical analysis as well as experimental validation. The nonlinear CDS generates harmonic current when the class-B/J drain voltage is applied across it, modifying the theoretical load trajectories on the Smith chart. This is shown to significantly deviate from the continuous-mode assertion of constant power and efficiency. A novel measurement approach called voltage-pull is used to investigate the effects of the second harmonic generation by the varactor in a class-B/J PA mode. Theoretical and experimental results showed the nonlinear CDS degrades the drain efficiency compared to class-B on one half of the class-B/J design space while improving the other half due to the energy upconversion and downconversion, respectively. This paper provides an approach for die nonlinear characteristic optimizations for transistor manufacturers.

Envelope tracking (ET) is a promising power amplifier (PA) architecture for current and future communications systems, which uses dynamic modulation of the supply voltage to provide high efficiency and potentially very wide bandwidth over a large dynamic range of output power. However, the dynamic nature of the supply voltage can lead to a problematic variation in transistor gain, particularly in GaN HEMTs. This paper describes and analyzes this behavior and the detrimental effect it can have on ET PAs. Contributing factors and origins of gain variation are described in detail along with how, for the first time, meaningful comparisons can be made between different devices. Using these guidelines, gain variation is shown to be a widespread issue effecting most GaN HEMTs presented in literature. To allow an analysis of the intrinsic device behavior, an extended transistor model is developed that takes the effect of gate and source field plates into account. This model is refined using measurement data and used to demonstrate the fact that the parasitic gate-drain capacitance (C _GD ) is the main contributor to the small-signal gain variation-a significant part of the overall gain variation. Based on this knowledge, possible strategies to reduce gain variation at the transistor technology level are proposed, allowing the optimization of GaN HEMTs specifically for ET PAs. One identified strategy involves reducing the length of the gate field plate and is shown to be a viable approach to reduce the gain variation in GaN HEMTs, albeit at an increased RF/dc dispersion.

We live in a fast-growing world of connected information technology that is represented by concepts such as 5G wireless communication, Internet of Things, as well as connected cars and healthcare. These technologies utilize a wide range of frequencies which encompass radio frequency, microwave, and millimeter wave bands. Concerns about the possible biological effects of microwave and millimeter wave frequencies on living organisms including humans, and their cellular, tissue, and organ functions persist, despite extensive investigations carried out for over 40 years.^{1 – 4} Published surveys of large human populations, although mainly concluding that effects are minimal,⁵ do not entirely dispel the need for cautious controls, e.g., on the use of mobile phones by children.⁶

Summary form only given, as follows. A new technique called Auxiliary Envelope Tracking (AET) is proposed, which demonstrates substantial improvement in linearity of RF power amplifiers. A small amplitude envelope-tracking voltage is superimposed on the fixed DC bias of a specially designed 25W GaN HEMT Class AB RF power amplifier (RFPA). A large improvement in third-order intermodulation (IM3) distortion has been observed while maintaining low fifth-order intermodulation (IM5). The overall drain efficiency of the RFPA is also observed to improve, even when the power consumption of the envelope tracking generator is included.