Microwave pulse compression using a helically corrugated waveguide

There has been a drive in recent years to produce ultrahigh power short microwave pulses for a range of applications. These high-power pulses can be produced by microwave pulse compression. Sweep-frequency based microwave pulse compression using smooth bore hollow waveguides is one technique of passive pulse compression, however, at very high powers, this method has some limitation due to its operation close to cutoff. A special helical corrugation of a circular waveguide ensures an eigenwave with strongly frequency dependent group velocity far from cutoff, which makes the helically corrugated waveguide attractive for use as a passive pulse compressor for very high-power amplifiers and oscillators. The results of proof-of-principle experiments and calculations of the wave dispersion using a particle in cell particle-in-cell (PIC) code are presented. In the experiments, a 70-ns 1-kW pulse from a conventional traveling-wave tube (TWT) was compressed in a 2-m-long helical waveguide. The compressed pulse had a peak power of 10.9 kW and duration of 3 ns. In order to find the optimum pulse compression ratio, the waveguide's dispersion characteristics must be well known. The dispersion of the helix was calculated using the PIC code Magic and verified using an experimental technique. Future work detailing plans to produce short ultrahigh power gigawatt (GW) pulses will be discussed

RF pulse compression using helically corrugated waveguides

This paper describes the use of a helically corrugated waveguide as a dispersive medium for microwave pulse compression. The helically corrugated waveguide has a large variation of group velocity with frequency, but in a region where the group velocity remains large. Therefore this compressor does not suffer from reflections associated with cut-off scenarios at frequencies close to its operating regime and may be used in conjunction with high power wideband tunable microwave sources and amplifier

Compression of frequency-swept microwave pulses using a helically corrugated waveguide

Microwave pulse compression is an important area of research in vacuum electronics, with important applications for linear accelerators, RADAR and non-linear testing. The principles and methods of pulse compression differ greatly depending on the application. The concept of producing ultra-high-power nanosecond microwave pulses, using passive sweep-frequency compression, was studied. A novel waveguide with a helical corrugation of its inner surface was used as the microwave pulse compressor. This structure couples a TE11 traveling wave with a near cut-off TE21 wave producing a region far from cut-off with a large change in group velocity with frequency. A 2.08 meter long copper helical waveguide was used to compress a 67ns, 5.7kW frequency-swept pulse from a high power TWT, driven by a swept solid-state source, to a 2.8ns 68kW pulse containing similar to 50% of the energy of the input pulse. The dispersion characteristics of the helically corrugated waveguide was investigated both experimentally and theoretically. A vector network analyser was used to measure experimentally the dispersion characteristics of complex waveguides and the code MAGIC was used to calculate the dispersion theoretically. Good agreement between experimental results and theoretical predictions was observed

Dispersion of helically corrugated waveguides: Analytical, numerical and experimental study.

Helically corrugated waveguides have recently been studied for use in various applications such as interaction regions in gyrotron traveling-wave tubes and gyrotron backward-wave oscillators and as a dispersive medium for passive microwave pulse compression. The paper presents a summary of various methods that can be used for analysis of the wave dispersion of such waveguides. The results obtained from an analytical approach, simulations with the three-dimensional numerical code MAGIC, and cold microwave measurements are analyzed and compared

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