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.

Figure 1

Schematic dispersion diagram for a helically corrugated waveguide.

Figure 2

Schematic view of a waveguide with a threefold right-handed helical corrugation.

Figure 3

Experimental and numerical results for the GTWT waveguide: (a) SNA measurements; (b) equivalent SNA MAGIC simulations.

Figure 4

Results of single-frequency MAGIC simulations for compressor waveguide 1 at frequency of $9.1\mathrm{GHz}$: (a) radial electric field distribution along a line shifted from $z$-axis by $0.15\mathrm{cm}$; (b) its spatial Fourier transform.

Figure 5

Dispersion characteristics for the GTWT waveguide.

Figure 6

Dispersion characteristics for compressor waveguide 1 (inset shows MAGIC approximation of the waveguide cross section).

Figure 7

Dispersion characteristics for compressor waveguide 2.

Figure 8

Dispersion characteristics for compressor waveguide 2 including the VNA measurements [inset shows the data from VNA before processing, including (solid line) and excluding (dashed line) an eight-period helix].