Yury Georgievich Yushkov

Development of High Power Microwave Compressors

Parameters of high power microwave compressors having a single storage cavity are presented for different frequency bands. Their resonant cavities operated with electrical field strength values close to critical ones which allowed par ex. to reach the output pulse power about 2 MW in Q- band and about 200 MW in S-band. Ways to go beyond these power values were considered. They were using asymmetrical TE-mode in a circular cavities, energy extraction through a multiport output element, the waveguide hybrid in this report, and series compression with resonant transfer of the energy stored in the first stage cavity.

Cryogenic resonant microwave compressors with energy extraction through “warm” interference switches

A method of switching cryogenic resonant microwavecompressors from the energy accumulation mode to the energy release mode is proposed and analyzed. The switching process is based on the resonant transfer of the microwaveenergy from a cryogenic storage cavity to a room temperature commutation cavity. The transfer can be realized using a cascade interference microwave switch weakly coupled to the storage cavity and consisting of two H-plane waveguide tees connected in series. The tees are made of a normally conducting material, located outside the cryostat, and contain commuting units in shorted side arms. The length of the cascade input arm (from the storage cavity to the first tee) is non-resonant, while the space between the storage cavity and the second tee is resonant. The weak coupling of the storage cavity to the cascade and the non-resonant length of its input arm allow one to minimize losses during the energy accumulation phase. When the commuting unit in the first tee is ignited, the tee opens, and the non-resonant volume of the cascade input arm is transformed into the volume of the resonant commutation cavity. The microwaveenergy is then transferred in a resonant way from the storage cavity to the commutation cavity, and when the transfer is complete, the commuting unit in the second tee is ignited to extract the energy into a load. It is shown analytically that, at a certain value of the coupling (the cryogenic storage cavity to the normally conducting cascade of tees) and length of the cascade input arm, the power gain in the storage cavity can be kept high. It is also shown that the energy accumulated in the storage cavity can be effectively transferred to the commutation cavity and from the commutation cavity to the load.

Multichannel Systems of Resonant Microwave Pulse Compression

Different designs of multichannel resonant microwave pulse compression systems operating in X- and S-bands are described. The output pulsed microwave power of these systems is expected to be severalfold greater than that of compression systems with a single output channel. These compression systems can be used as compact sources of high-power nanosecond-duration microwave pulses, sources of synchronized sequences of microwave pulses, and sources for development of phased arrays of compressed microwave pulses. In particular, the authors describe the characteristics of a two-channel S-band resonant microwave pulse compression system with nanosecond-duration output pulse and an output pulsed microwave power of 1 GW. The operation of a four-channel X-band compression system with a possible eightfold output pulsed microwave power increase, relatively to the microwave power in the cavity, is also described. The design of an eight-channel system with a 16-fold output pulsed microwave power increase is reviewed. The parameters of an X-band compression system with multichannel output unit formed as a set of interference microwave switches extracting the energy in synchronism are presented.

Forming Nanosecond Microwave Pulses by Transformation of Resonant Cavity Mode

The microwave pulse compression procedure consists of excitation of a working mode in a resonant cavity and transforming the mode into an auxiliary one that is coupled to an output line. Both transforming and coupling involve switching. Transients were calculated by recursion relations giving higher accuracy at short time constants. Demonstration experiments were run in the X-band. The compressor prototype showed power amplification of 15 dB at an output pulse width of 2.7 ns and a peak power of 1.5 MW. Mode transformation efficiency approached 0.7. A sequence of nanosecond and sub-nanosecond microwave pulses within the length of an input feeding pulse can be, in principle, obtained.

Formation of high power microwave pulses with adjustable parameters in active X-band RF compression systems

The work presents the results of theoretical and experimental studies of the formation of microwave pulses with the adjustable power, duration, repetition rate and the envelope form during energy output from the cavity by controlled transformation of the oscillation mode at the waveguide stub coupling aperture. Pulse parameters are changed by adjustable elements of the coupling of modes, which directly affect to the coefficient of the coupling of modes h. The possibility to form a series of subnanosecond MW pulses at a fractional energy output and nanosecond pulses of various pulse duration at a single complete output of high frequency energy from the compressor cavity is demonstrated. The envelope of the pulses is calculated through the recurrence relations between the amplitudes of waves in the system, the relations between which have been recorded according to the scattering matrix method. Using this approach on passive X-band RF pulse compression system, we obtained power gain of 8-9 dB, 8-10 ns pulse duration at 9.248 GHz.

Oversized interference switches of active resonant microwave compressors

Interference switches of resonant microwave compressors made of single mode waveguides provide high coupling factors after switching and rapid energy extraction. The disadvantage of these switches is low electrical strength which limits output power values. Oversized waveguides maintain higher electrical strength due to large dimensions of a cross section but mode transformation disturbs the regular operation of the switch. Operation of interference switches with a gaseous discharge gap as a switching element in oversized rectangular waveguides was studied experimentally. Conditions of their effective switching in active resonant microwave compressors were derived. It was shown that the stable microwave pulses of gigawatt power level in S-band and pulses of 0.1 GW pulse power in X- band can be produced in resonant microwave compressors with oversized interference switches. Possible switch designs are discussed.

Development of microwave pulse compressors

The microwave pulse compression uses the capability of a resonant cavity for amplification of the field strength of an exciting falling wave about 20 dB and beyond. Basics of microwave pulse compressor operation and main parameters achieved are presented.