The High-Power O-Type mm-wave Oscillators for Process Applications

The expediency of application of resonant TWTs in the processing devices of mm-wave range is considered. The basic design of the permanent magnet-packaged oscillator having CW-power of 1.5 kW at 34 GHz has been developed. Lately there has been observed an increase of interest to the use of electromagnetic microwave fields for thermal processing of ceramics. Sutton (1). The devices operating at 2.45 GHz are the most widely spread, however there have appeared certain reports on the use of higher frequency setups operating at 28 and even at 60 GHz. The advantages of the mm-range are conditioned by the increase in absorption of electromagnetic waves in media as frequency rises (1): P = 2¿f¿o¿¿rtg¿/E/2 where P is the power, absorbed by unit volume, W/m3, f is the operating frequency, Hz, ¿o is the dielectric constant of free space, F/m, ¿¿r is the relative dielectric constant of the medium, tg¿ is the tangent of dielectric losses of the medium, E is the value of the internal electric field, V/m. When ceramic samples to be processed have low dimensions the efficacy of the mm-wave application increases: D= 3¿o/8,68¿tg¿(¿¿r/¿o)¿ where D is the depth of penetration of the EM-wave into a substance, at which its energy is reduced by one half, ¿o is the operating wavelength in free space.