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Abstract The effects of 5.8-GHz microwave (MW) irradiation on the synthesis of mesoporous selenium nanoparticles (mSeNPs) in aqueous medium by reduction of selenite ions with ascorbic acid, using zinc nanoparticles as a hard template and cetyltrimethylammonium bromide (CTAB) as a micellar template, are examined for the first time with a particular emphasis on MW-particle interactions and the NPs morphology. This MW-assisted synthesis is compared to 2.45 GHz MW heating method and conventional hydrothermal method at around 100 °C to produce the nanoparticles of different morphology and particle size distributions. The NPs morphology is tailored by varying the temperature ramp characteristics and the MW irradiation time. Under mild synthesis conditions only spherical particles are formed. Enhancing temperature ramp rate in the presence of CTAB micelles increases the metal–semiconductor hybrid particles growth rate and promotes the formation of nanorods and branched shapes. The effect is MW frequency dependent and non-thermal to some extent. Multi-step mechanism of mSeNPs formation is proposed based on derivative UV–Vis spectrophotometry and scanning electron microscopy (SEM) data. Both the stability of the chemical composition at a single particle level and the high efficiency of zinc template removal are determined by single particle microwave plasma optical emission spectrometry (SP-MWP-OES). After Zn template removal mSeNPs can be loaded with antifungal carbamate agent, hence the application as a nanopesticide is suggested.

The paper presents the two transmitter analog paths of 10 W and 400 W peak output power developed for micro- and macro-cell LTE450 base stations, respectively. Each path contains a chain of amplifiers with a final stage designed in the Doherty architecture to improve total transmitter power efficiency. The paths were optimized for linearity and efficiency considering, i.e., an output power vs. input power course shape and tuning of the amplifier's operating points while using low computational complexity MP algorithms.

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.

Permittivity, the dielectric loss tangent and conductivity of semi-insulating Gallium Nitride crystals have been measured as functions of frequency from 10 GHz to 50 GHz and temperature from 295 to 560 K employing quasi TE0np mode dielectric resonator technique. Crystals were grown using ammonothermal method. Two kinds of doping were used to obtain high resistivity crystals; one with deep acceptors in form of transition metal ions, and the other with shallow Mg acceptors. The sample compensated with transition metal ions exhibited semi-insulating behavior in the whole temperature range. The sample doped with Mg acceptors remained semi-insulating up to 390 K. At temperatures exceeding 390 K the conductivity term in the total dielectric loss tangent of Mg compensated sample becomes dominant and it increases exponentially with activation energy of 1.14 eV. It has been proved that ammonothermal method with appropriate doping allows growth of high quality, temperature stable semi-insulating GaN crystals.

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 Ω ·mm. Good microwave performance was obtained due to the absence of parasitic elements such as high access resistance.

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.

In the paper a balanced high power amplifier with class A silicon bipolar transistors for L-band T/R module is described. The amplifier was designed for maximum power and minimum transmitance distortions. The obtained parameters of the amplifier are as follow: output power at 1 dB compression P1 dB > 49 dBm, linear gain |S21| > 10 dB, and transmitance deviations during the RF pulse: phase arg(S21)