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This paper describes two approaches which have been developed in the past few years for the creation of electronically controlled steering of the microwave beam formed by multichannel auto-oscillators. The first one is based on two- and four-channel gyromagnetic nonlinear transmission lines operating in the generation mode at subgigawatts power level and decimeter wavelengths. The second approach uses Cherenkov superradiance in two and four parallel backward-wave oscillators with centimeter wavelengths. We present the results of several recent experiments and analyze the physical and technical limitations to arrange new radiating arrays.

The effective 1-s batch of 100-Hz pulse repetition rate mode of an X-band relativistic backward-wave oscillator with a resonance reflector (RBWO-RR) was realized using the “SINUS” pulse-periodic nanosecond accelerator allowing mechanically installed high voltage pulse length of 13 and 42 ns. Magnetic held about of 2 T was produced by two-section solenoid to transport the electron beam along RBWO-RR electrodynamic system. T M01 to T E11 mode converter connected to the oscillator output allowed Gaussian radiation pattern. The microwave oscillator allowed producing the microwave pulse length of 4.7 and 29 ns. The energy of the microwave pulse measured by the X-band aperture calorimeter was 1.4 or 6.3 J corresponding to the mentioned above microwave pulse length of 4.7 or 29 ns, respectively. That allowed estimations of the microwave peak power as high as 280 ± 30 MW and 210 ± 20 MW related to the pulse lengths. The efficiency of the oscillator was 23-25%. A possibility of the microwave pulse length fine tuning within 25 to 34 ns range in the “long pulse mode” by changing the solenoid magnetic held conhguration was shown.

Operation of explosive-emission cold cathodes made from various materials was studied at a large number of pulses at current densities of /spl sim/1.0/sup 4/ A/cm/sup 2/. The cathode voltage and the beam current were /spl sim/500 kV and 5 kA, respectively, with a pulsewidth of /spl sim/20 ns. At a small number of pulses (/spl les/10/sup 3/), cathodes of like geometry (even made from different materials) demonstrated similar emission properties. For most of the materials tested, with a large number of pulses (/spl ges/10/sup 3/), the current risetime increased to the fullwidth of the voltage pulse and the maximum current of the vacuum diode decreased. When using a graphite cathode, the maximum current remained invariant until 10/sup 8/ pulses. Mass losses were measured for a series of cathode materials. The results obtained offered the possibility to realize long-lived operation of an X-band relativistic backward-wave oscillator with an almost invariant output power of 350-400 MW during 10/sup 8/ pulses at a pulse repetition rate of 100-150 p.p.s.

Results from a study of a relativistic X-band backward-wave oscillator (RBWO) with 3-GW output microwave power are presented. The RBWO was driven by the high-current electron accelerator SINUS-7. The dependence of radiated microwave pulse duration on microwave power was obtained. Pulse shortening occurring at the higher power levels is probably attributable to explosive electron emission from the slow wave structure (SWS). An increase in the cross section of the electrodynamic structure seems to be a way to increase the microwave pulse duration. Experimental results from a moderately oversized X-band RBWO using a resonance reflector are described. This tube can be operated with a low external magnetic field.