AlGaN/GaN high electron mobility transistors on semi-insulating bulk ammonothermal GaN have been investigated. By application of regrown ohmic contacts, the problem with obtaining low resistance ohmic contacts to low-dislocation high electron mobility transistor (HEMT) structures was solved. The maximum output current was about 1 A/mm and contact resistances was in the range of 0.3–0.6 $\Omega$ ·mm. Good microwave performance was obtained due to the absence of parasitic elements such as high access resistance.

Thermal characterization of modern microwave power transistors such as high electron-mobility transistors based on gallium nitride (GaN-based HEMTs) is a critical challenge for the development of high-performance new generation wireless communication systems (LTE-A, 5G) and advanced radars (active electronically scanned array (AESA)). This is especially true for systems operating with variable-envelope signals where accurate determination of self-heating effects resulting from strong- and fast-changing power dissipated inside transistor is crucial. In this work, we have developed an advanced measurement system based on DeltaV_GS method with implemented software enabling accurate determination of device channel temperature and thermal resistance. The methodology accounts for MIL-STD-750-3 standard but takes into account appropriate specific bias and timing conditions. Three types of GaN-based HEMTs were taken into consideration, namely commercially available GaN-on-SiC (CGH27015F and TGF2023-2-01) and GaN-on-Si (NPT2022) devices, as well as model GaN-on-GaN HEMT (T8). Their characteristics of thermal impedance, thermal time constants and thermal equivalent circuits were presented. Knowledge of thermal equivalent circuits and electro–thermal models can lead to improved design of GaN HEMT high-power amplifiers with account of instantaneous temperature variations for systems using variable-envelope signals. It can also expand their range of application.

Power amplifiers applied in modern active electronically scanned array (AESA) radars and 5G radios should have similar features, especially in terms of phase distortion, which dramatically affects the spectral regrowth and, moreover, they are difficult to be compensated by predistortion algorithms. This paper presents a GaN-based power amplifier design with a reduced level of transmittance distortions, varying in time, without significantly worsening other key features such as output power, efficiency and gain. The test amplifier with GaN-on-Si high electron mobility transistors (HEMT) NPT2018 from MACOM provides more than 17 W of output power at the 62% PAE over a 1.0 GHz to 1.1 GHz frequency range. By applying a proposed design approach, it was possible to decrease phase changes on test pulses from 0.5° to 0.2° and amplitude variation from 0.8 dB to 0.2 dB during the pulse width of 40 µs and 40% duty cycle.

This paper presents a universal hardware platform (UHP) based on software defined radio (SDR) technology and developed to accelerate the prototyping and testing new hardware and algorithmic solutions for modern radio systems. There are two integrated transceivers and a baseband processor on the board. Thus, four complete RF transmitting and receiving channels, with observation paths for transmitted signals monitoring could be supported. Our platform can be operated in both time-division (TDD) and frequency-division (FDD) duplex schemes over a 300 MHz to 6 GHz frequency range with simultaneous synthesis and analysis in the bandwidth of up to 100 MHz. The radio system is formed by attaching an appropriate RF front-end to the UHP and uploading standard-specific software. As examples of possible UHP applications, two LTE-Advanced micro base stations for private networks with standard-defined RF front-ends operating in the LTE band B43 (3.6 GHz) with time duplex and the band B31 (450 MHz) in FDD mode are presented.

The ability of microwaves to heat various kinds of substances has been known for decades [1] . Today, this phenomenon is used in many technological and scientific fields, such as food processing (both in home-use microwave ovens and large industrial installations) [2] , wood drying [3] , medicine (microwave ablation treatment) [4] , and waste recycling (pyrolysis) [5] , just to name a few. Opportunities for new applications are emerging with technological advances allowing for increasingly precise manipulation of microwave signals.

This paper describes development of solid-state microwave power test system (MPTS) operating over 2.3 to 2.6 GHz with the output power level of 100 W for industrial applications in material processing, and for designing of microwave power industrial equipment. The MPTS unit consists of four major parts: PLL synthesizer, high power solid-state amplifier, detector probes for return losses and leakage measurement and microcontroller. The MPTS system is able to operate in either single fixed-frequency regime, or in swept mode with self-tuning for minimum reflection of a heated load.