Some surprising helical interaction circuits may hasten millimeter waves

Spurred on by the need for affordable broadband power at millimeter wavelengths, the long dormant helix loaded waveguide interaction circuit is making a comeback. It is one circuit which deserves a long, hard second look for numerous reasons; high peak and average power capability, low part count, ease of fabrication, and insensitivity to tolerance variations. The helix loaded waveguide is closely related electrically to the many forms of the transmission line helix. Somewhat more surprising, it can be derived from a helically coiled double ridge waveguide, an as yet untested interaction circuit which has theoretical design and performance characteristics much like those of the fast wave gyro TWT. In fact, it may be an attractive alternative to the fast wave TWT for numerous applications.