MicroWave Spectroscopy Laboratory

Instruments 35-400 GHz range

Frequency stabilization and control system for backward-wave oscillators (BWO) of 35-400 GHz range

The device is designed by analogy with, and as a continuation of the series of "Kvarz" synthesizers [Ref. 12 (1994)] (Device 005).

Block-diagram of 35-400 GHz frequency synthesizer

Conventional BWO tubes from "Istok" (Fryazino, Moscow region) are used. For non-packetized tubes of the type OB-24 or OB-30 we developed a compact permanent magnet system (Device 003). The output radiation of the tube is stabilized by a phase locked loop (PLL) system against harmonic of 10-12 GHz signal. This signal is generated either by commercial or home-made synthesizer.
The base block of "Kvarz" synthesizer may be used. The base block produces also a signal for the BWO power supply to direct the radiation of the tube to required frequency range where it will be automatically entapped and locked by the PLL system. Further precise control of the tube output radiation is performed by controlling the 10-12 GHz signal of the base block by PC through GPIB interface.
Fast digital frequency sweeping of output radiation within 200 MHz range is possible using a radio frequency (20-50 MHz) fast direct digital synthesizer as a reference signal source for the synchronizer (Device 012). The multiplier-mixer is of balance type based on a couple of planar Schottky diodes glued on a strip-line inside a wave-guide. Transmission-type mixers are used for 35-178 GHz range sources (Device 017). Quasioptical waveguides are used in a higher frequency rage (Device 013). Workability of the synthesizer in such configuration was demonstrated up to 500 GHz. Main parameters of the synthesizer output radiation are the the following: relative frequency stability - 10 ppb with inner reference quartz oscillator or higher with the use of external 5 MHz signal from rubidium or hydrogen standard; radiation bandwidth - 1 kHz; minimal frequency step 100 Hz; output power 5-50 mW (depending on BWO output). The synthesizer allows either amplitude or frequency modulation of output radiation. Fast digital frequency scanning with continuous phase (see block-diagram here) is possible as an option.

BWO radiation spectral characteristics

   Institute of Applied Physics of the Russian Academy of Sciences
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