Numerical and Experimental Validation of the Passive Performance of a Coharmonic Gyro-Multiplier Interaction Region

• Published in: IEEE transactions on microwave theory and techniques Vol. 69; no. 10; pp. 4377 - 4384
• Main Authors: Constable, David A., Phelps, Alan D. R., Whyte, Colin G., He, Wenlong, Cross, Adrian W., Ronald, Kevin
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-10-2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Bandwidths; Converters; Cutoff frequency; Cyclotron resonant masers; electromagnetism; Electron beams; Frequency conversion; Geometry; gyrotrons; Harmonic analysis; Harmonics; microwave measurements; Microwave theory and techniques; mode convertors; Polarization; Purity; Quadrupoles; Scattering parameters; Waveguides
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2021.3094219

The azimuthally rippled cavity for a large-orbit, coharmonic gyro-multiplier, designed to operate at the second and fourth harmonics, at frequencies of 37.5 and 75 GHz, respectively, has been numerically and experimentally confirmed to be insensitive to the polarization of quadrupole, <inline-formula> <tex-math notation="LaTeX">{\text{TE}}_{2,n} </tex-math></inline-formula>-like modes, including the second-harmonic operating mode of the multiplier, a cylindrical TE 2,2 -like waveguide mode. To test the cavity with this mode required the design, construction, and measurement of ripple wall mode converters, converting the cylindrical TE 2,1 mode into the TE 2,2 mode. These were designed to operate at a central frequency of ~37.9 GHz, with predicted mode purity of better than 85%, and 3-dB bandwidth of 161 MHz. The constructed converter had a central operating frequency of 37.7 GHz, with <inline-formula> <tex-math notation="LaTeX">S </tex-math></inline-formula>-parameter measurements used to infer suitable mode purity and an operational 3-dB bandwidth of 50 MHz. This has allowed far-field phase measurements of the corrugated cavity to be conducted, where the orientation of the geometry to the polarization of both the TE 2,1 and TE 2,2 modes was shown to have no effect on the dispersion.