Design concepts for an octave-bandwidth coupled-cavity TWT

Abstract

To obtain an octave of instantaneous bandwidth in a coupled-cavity TWT, the circuit must exhibit sufficiently low dispersion over a corresponding "cold" bandwidth. Gain flatness over the "hottt bandwidth must also be assured along with electronic stability. Design concepts capable of meeting these needs, and supported by analytical and cold-test results, are introduced.A coupled-cavity structure meeting the coldbandwidth and dispersion requirements was developed with little difficulty. Within the band, a 2n-point backward-wave instability requires suppression by nonreciprocal means. Ferrimagnetic spheres internal to the circuit can promote stability through a combination of backward-wave absorption and diminished backwardwave Pierce impedance near the selected frequency. Alternatively, novel external circuitry directionally coupled to the side of the TWT can create an effective ttsevertt affecting only backward waves at the selected frequency.

The dynamics of merge and inversion of cavity and slot modes in coupled cavity chain slow wave structure

“…In contrast to our previous works [9], the combination of the CCC cavity and slot passbands, as well as their inversion (the case when the resonant wavelength of the slots becomes larger than the cavity's own wavelength), was carried out in the traditional way of simultaneously reducing the cavity diameter and increasing the opening angle of the coupling slot (see works [1,2,4,5]).…”

“…CCC with two sets of bandwidths: cavity and slot wave types, can be used in TWT in various operating modes. When the main cavity and slot passbands of CCC merged, a significant increase in its working passband was obtained in [1][2][3] (up to 70% when the phase velocity changes within ± 3%). The transition to the inverted slot mode slow wave structure (SS) significantly changes the properties of CCC and, accordingly, the functional application in TWT when suppressing excitation at the short-wavelength boundary of the working band [4,5].…”