Microwave Compressor Research Articles

Formation of Rectangular Pulses in an Active Microwave Compressor With an Oversized Compact Storage Cavity

The microwave compressor of a new design forms high-power rectangular pulses of a spatial length exceeding several folds the longitudinal dimension of a storage cavity. Similar to the known compressor with the single-mode circular cavity, the new one has small overall dimensions due to making the cavity as a meander formed by parallel waveguide sections. The input coupler is the input port of the first section, and the output unit is the output port of the last section. Unlike the known compressor, the waveguide elements of the proposed one are oversized. Requirements for the design are determined and characteristics are estimated. Comparing with the analog compressor, the gain of the proposed one is greater by 7 dB. The processes of energy storing and extraction and the characteristics of the X-band compressor were analyzed by computer simulation. The compressor was tested experimentally, and the results were compared with the simulation data. It was shown that the microwave compressor with the oversized compact cavity worked similar to the analog compressor.

Interference Switch of a Resonant Microwave Compressor with Distributed Switched Wave Power

Abstract—An analysis is performed for the characteristics of an interference microwave switch with distributed switched wave power as a device for outputting energy from an active resonant microwave compressor. The proposed device is a cascade of conventional microwave switches based on H-tees connected in series with straight arms. It is shown that such a switch can multiply reduce the switched wave power by uniformly distributing it across the switches of the tees, which is done by adjusting the lengths of the tee arms. It was also established that between the lengths there is a functional relationship in which uniform distribution is achieved. The results of an experimental study of the microwave switch of two and/or three tees at low and high power are presented.

Gaseous discharge plasma switching in oversized interference microwave switches

The first results of the study of gaseous discharge plasma switching in oversized interference switches of X-band active resonant microwave compressors are presented. The switching occured in a mixture of argon and air at atmospheric pressure in the mode of spontaneous breakdown. The breakdown was initiated by a sizable conductive discontinuity represented by a section of thin copper conductor of different lengths not exceeding the working wave length. The section was introduced inside the gaseous discharge quartz tube into the switching arm of the switch through the below cut off circular waveguide. The tube formed the discharge gap in the arm and was located coaxially in the circular waveguide. The tube was located at the antinode area of the electric field standing wave parallel to lines of electric force. The threshold nature of effective switching was proved. The switching efficiency as a function of the conductor length is obtained. The model of the switch was proposed and analyzed by the scattering matrix method within single-wave approximation. The calculation results were in substantial agreement with the experimental data. The operation of two oversized switches in a cascade circuit was studied. It is shown, that in switching circuits of these type formed by one or several oversized H-tees, the switching identical to processes in a conventional switch based on a single-wave H-tee is possible.

Compact Active S-Band Microwave Compressors for Producing Rectangular Pulses of Up To 100 ns

This paper proposes and describes in detail a new approach to the design of very compact active microwave compressors capable of providing rectangular pulses of up to 100 ns. The approach consists in using a storage cavity, which comprises linear waveguide sections connected by tees such that the cavity geometry can be 2-D or 3-D or can be variable to allow direct space-saving integration of a compressor into a microwave source. Also presented are the scattering matrix data on uniform wave propagation along the storage cavity with little reflection and on conditions necessary for such uniformity. The S-band experiments demonstrate the capability of storage cavities with two and three parallel waveguide sections of about 1 m long to produce rectangular pulses of duration 5, 15, and 25 ns with a power gain and output power of about 16 dB, 80 MW; 15 dB, 60 MW; and 13 dB, 40 MW, respectively. Our estimates suggest that 12 waveguide sections can provide a rectangular pulse of 100 ns with a power gain 10 dB.

Interference Switch of a Superconducting Resonance Microwave Compressor

We propose a superconducting interference switch of a resonance microwave compressor on the basis of a waveguide H-plane tee, whose lateral arm contains a switching cavity having controllable parameters and based on another H-plane tee. The transmission coefficient of the switch is evaluated for the case of controlling the Q-factor and/or resonance frequency of the switching cavity externally. It is shown that the proposed switch can ensure high-efficiency transmission of the stored energy to the load at a minimal value of the controlling parameter (compared with the known solutions).

Gain and Efficiency of a Superconducting Microwave Compressor with a Switching Cavity in an Interference Switch

We study the processes of radiation output from a microwave storage cavity through a superconducting interference switch, which is based on a H-junction with a superconducting switching cavity connected to the side branch of the junction for various ways of controlling the parameters of the switching cavity. It is shown that efficient control over radiation output in such a switch can be achieved by varying the resonance frequency or Q-factor of the switching cavity, as well as by varying these parameters simultaneously. It is found that in the case of controlling the resonance frequency of the switching cavity, there exists an optimal interval of the frequency variation, within which the total efficiency and extraction efficiency are maximum. When the Q-factor of the switching cavity changes, the dependence of the total efficiency and extraction efficiency on the Q-factor has the monotonic character. The mixed regime of radiation output control is also studied. The envelopes of the output compressor pulses are plotted on the basis of recurrent relationships between the amplitudes of the waves in the system for three regimes of switch operation. It is shown that pulses with an almost rectangular shape of the envelope can be formed in the regime of controlling the switching cavity by varying the Q-factor. An example of possible realization of the switching cavity is considered.

Improved operation of a microwave pulse compressor with a laser-triggered high-pressure gas plasma switch

The influence of laser beam parameters on the output pulses of a resonant microwave compressor with a laser-triggered plasma switch was investigated. The S-band compressor, consisting of a rectangular waveguide-based cavity and H-plane waveguide tee with a shorted side arm, was filled with pressurized dry air and pumped by 1.8-μs-long microwave pulses of up to 450 kW power. A Nd:YAG laser was used to ignite the gas discharge in the tee side arm for output pulse extraction. The laser beam (at 213 nm or 532 nm) was directed along the RF electric field lines. It was found that the compressor operated most effectively when the laser beam was focused at the center of the switch waveguide cross-section. In this case, the power extraction efficiency reached ∼47% at an output power of ∼14 MW, while when the laser beam was not focused the maximal extraction efficiency was only ∼20% at ∼6 MW output power. Focusing the laser beam resulted also in a dramatic decrease (down to <1 ns) in the delay of the output pulses' appearance with respect to the time of the beam's entrance into the switch, and the jitter of the output pulses' appearance was minimized. In addition, the quality of the output pulses' waveform was significantly improved.

A Study of Interaction of an Electron Beam with a Strong High-Frequency Field in the Waveguide Switch of a High-Power Microwave Compressor

We present the results of simulating numerically the operation of a high-power active compressor of microwave radiation pulses in the 3-cm wavelength band with a waveguide switch activated by an electron beam. The influence of the nonlinear character of electron beam interaction with the high-frequency field in the switch on the output parameters of the compressor is discussed, and the simulation results are compared with the experimental data. It is shown that at a high power of the input radiation, the effect of electron expulsion from the region of the inhomogeneous field in the switch can lead to a decrease in the compressor gain and elongation of the leading front of the compressed pulse.

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

A method of switching cryogenic resonant microwave compressors 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 microwave energy 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 microwave energy 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.

Analysis of microwave interference switches with distributed power of switched wave and plasma gas-discharge switching

This paper reports on development of effective cascade type microwave interference switches using waveguide H-tees providing total transition attenuation value of about -50dB at the non-transmitting state, the power losses of -2-3dB at the transmitting state, and the working power compared to the one of a regular waveguide. These switches have different types of connections of two or three H-tees. Different designs provide different distributions of switched wave power between tees and provide different power levels of the switched wave. Characteristics of the switches made of tees matched from their side arms and of unmatched ones were calculated using the scattering matrix method. It was shown the matched tees used in the design allow decreasing by several times the power level of the switched wave and that increases the operating power and stability of the switching process. While some definite combination of unmatched tees allow increasing the power level of the switched wave and may provide effective switching of the transmitted wave at decreased power level. It was shown experimentally the cascade switches could be used as effective energy extraction device in an active resonant microwave compressor also.

Analysis of microwave energy extraction process at the resonator with controlled transformation of oscillation modes

It is considered an operation of resonance microwave compressor with extraction of energy by means of controlled transformation of oscillations modes on a coupling window of the resonator with short-cut waveguide stub. Using dispersion matrix method with a device model we carried out the analysis of the extraction process in case of transformation of high-Q mode into down to the limit low-Q mode. There are obtained the expressions for description of the transient processes during accumulation and extraction processes. It is shown researched compressor is possible to shape the microwave pulses with controlled power, duration and envelope shape.

Experimental Study of High-Current Cathodes Based on Diamond Films as Elements of High-Power Compressors of Microwave Pulses

We present the results of studying the emissive properties of molybdenum cathodes with deposed diamond films at strong currents, as well as the dependences of these properties on the deposition regimes and the structure of diamond films. The emissive properties of the films are determined by analyzing the output parameters of a high-power compressor of microwave pulses, which is based on diamond-coated cathodes. It is shown that the use of such cathodes allows one to increase the emission current and the amplification factor of the microwave compressor.

High Power Microwave Compressor with Two Output Units for Synchronous Energy Extraction

The compressor contains the oversized cylindrical cavity with two interference output units each in the figure of a circular waveguide H-tee. The H-tees are coupled by a waveguide section and the energy is extracted synchronously through two output ports. The synchronism is provided through using a single microwave switch mutual for both H-tees. Simulation and experimental study of the X-band microwave compressor were carried out. The simulation made it possible to optimize the configuration of the oversized storage cavity and the output element. The amplification factor was 14 dB when the energy was extracted though one output unit at the output pulsewidth of 6...7 ns. Amplification factor and the output power were increased by 2dB and the pulsewidth was decreased down to 3...3.5 ns when the energy was extracted synchronously through two output units.

Plasma density temporal evolution in a high-power microwave pulse compressor switch

Time-resolved optical-emission spectroscopy measurements are used to evaluate plasma density in an interference switch during the extraction of a nanosecond output pulse from a high-power microwave compressor. The compressor represents a resonant cavity connected to an H-plane waveguide tee with a shorted side arm filled with helium at a pressure of ; the plasma discharge in the tee side arm is triggered by a Surelite laser. A nanosecond-scale dynamics of the plasma density is obtained by analyzing the shape of the helium spectral lines. The analysis of the experimental data evidences a correlation between the rise time of the plasma density and the peak power of the microwave output pulse. Numerical simulations of the microwave energy release from the cavity with the appearance of the plasma yield results in good agreement with the measured output pulse peak power and waveform.

Stabilized Operation of a Microwave Compressor Driven by Relativistic S-Band Magnetron

The stabilized operation of a microwave compressor based on a travelling wave resonator, producing at its output microwave pulses with a power of 1.15 ± 0.05 GW and duration of 12 ± 2 ns, is described. The compressor is pumped by a relativistic S-band magnetron generating microwave pulses with a power up to 250 MW and duration of ~100 ns. To stabilize the frequency of the microwaves generated by the magnetron, a transparent cathode having a limited electron emission surface and double ring-type straps between the anode resonators were applied. It was shown that the application of a phase-shifter between the magnetron and resonator results in the influence of the positive feedback on the magnetron operation beginning within the first 10 ns of the microwaves generation. Finally, the incorporation of symmetrically placed phase-shifters in the compressor's resonator allows the travelling wave phase to be adjusted, and accordingly, reliable ignition of the microwave gas discharge switch.

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.

Switching of Microwave Radiation Storage and Output Modes in Superconducting Resonance-Cavity Compressors with an Interference Switch

UDC 621.37 We propose a commutator for the interference switch of microwave electromagnetic radiation on the basis of a waveguide H-junction made as a cavity with tunable parameters, which is connected to one arm of this junction. The superconducting version of a microwave compressor with such a switch is analyzed. The conditions of effective switch operation in the mode of electromagnetic energy storage and its fast output in the case of controllable manipulation of the Q-factor and resonant frequency of the switching cavity are determined. Estimates of the output parameters of the superconducting compression system are presented for storing- and switching-cavity Q-factors of about 5 · 10 8 . The possibility of increasing the radiated power in such a compression system by 40–60 dB for output microwave pulses with durations of about 5–10 ns is demonstrated. Variants of practical implementation of the system are considered.

Numerical simulations of output pulse extraction from a high-power microwave compressor with a plasma switch

Numerical simulations of the process of electromagnetic energy release from a high-power microwave pulse compressor comprising a gas-filled cavity and interference switch were carried out. A microwave plasma discharge in a rectangular waveguide H-plane tee was modeled with the use of the fully electromagnetic particle-in-cell code MAGIC. The gas ionization, plasma evolution, and interaction with RF fields accumulated within the compressor were simulated using different approaches provided by the MAGIC code: particle-in-cell approach accounting for electron-neutral collisions, gas conductivity model based on the concept of mobility, and hybrid modeling. The dependences of the microwave output pulse peak power and waveform on parameters that can be controlled in experiments, such as an external ionization rate, RF field amplitude, and background gas pressure, were investigated.

Synchronous extraction of microwave energy from cavities through a packet of interference switches

Synchronous extraction of energy from cavity resonators for X-band microwave radiation through a compact packet of five interference switches based on H tees has been experimentally analyzed. It is shown that switches can be completely synchronized and the synchronization conditions are determined. Microwave pulses have been generated upon synchronous extraction of energy from five single-mode cavities (power ∼0.8 MW, gain ∼12 dB, and width ∼3.2 ns) and from one superdimensional cavity (power ∼2.2 MW, gain ∼16.5 dB, and width ∼3.5 ns). The operation limits of X- and S-band microwave compressors with extraction of energy through a packet are estimated.

Charging of the Traveling Wave Resonator of the Microwave Compressor by a Relativistic S-Band Magnetron

The charging of the traveling wave resonator (TWR) of a microwave compressor by a relativistic S-band magnetron that generates microwave pulses with power ≤ 250 MW and duration of ~ 100 ns is described. The short pulse duration determining the resonator charging time and traveling electromagnetic wave increases the electric strength of the resonator. The short duration of the input pulse determines the coupling and Q-factor of the TWR, and it is not necessary to apply an interference switch for energy release. A scheme for releasing energy at a microwave power of ≥ 1 GW using a ferrite circulator is discussed.