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A microwave system in the form of a quasi-optical (QO) transmission line is proposed as an interaction circuit of an amplifier or an oscillator based on the cyclotron resonance maser (CRM) instability. The circuit consists of periodically spaced along the horizontal ${z}$ -axis focusing mirrors, which transport the Gaussian wave beam along a zigzag path with vertical and inclined segments. A beam of electrons having sufficiently high perpendicular velocities is guided by a static B-field along the ${z}$ -axis so that the e-beam periodically crosses the wave beam. The CRM instability occurs in regions where an electromagnetic wave having a Bz-component, as in a gyrotron, propagates strictly across the e-beam resulting in the interaction with minimal sensitivity to particle velocity spread. Three-dimensional Particle-In-Cell (3-D PIC) simulations demonstrate the attractiveness of this “zigzag” CRM for the implementation of relatively broadband amplifiers or oscillators with unique (more than an octave bandwidth) frequency tunability at wavelengths of 1–2 mm.

The dielectric loss and refractive index in the monocrystal silicon carbide of the polytype 6H–SiC were studied in the 6–380 GHz frequency range and the 300–850 K temperature interval using high-quality resonator techniques. At low frequencies (f 50 GHz), the loss increases with frequency. The loss nature in wide frequency and temperature ranges is considered. The possibility to apply silicon carbide for production of high-power windows is investigated.