Equivalent Circuit Analysis of Serpentine Folded-waveguide Slow-wave Structures for Millimeter-wave Traveling-wave Tubes

Abstract

A simple equivalent circuit model for the analysis of dispersion and interaction impedance characteristics of serpentine folded-waveguide slow-wave structure was developed by considering the straight and curved portions of structure supporting the dominant TE 10 -mode of the rectangular waveguide. Expressions for the lumped capacitance and inductance per period of the slow-wave structure were derived in terms of the physical dimensions of the structure, incorporating the effects of the beam-hole in the lumped parameters. The lumped parameters were subsequently interpreted for obtaining the dispersion and interaction impedance characteristics of the structure. The analysis was simple yet accurate in predicting the dispersion and interaction impedance behaviour at millimeter-wave frequencies. The analysis was benchmarked against measurement as well as with 3D electromagnetic modeling using MAFIA for two typical slow-wave structures (one at the Ka-band and the other at the W-band) and close agreement observed.

The Analytical Design of a Folded Waveguide Traveling Wave Tube and Small Signal Gain Analysis Using Madey's Theorem

“…The FWTWT device as an input parameter into Equation (37) has 220 number of folds, N . The calculations from Equation (37) show that the maximum electronic gain is 20.26, or equivalent to 13.1 dB. This occurs at 543.9 GHz, and is shown in Figure 8.…”

“…An electron beam is passed through the FWTWT from left to right, in the +z direction, as shown in Figure 6. The interaction between the electron beam and the EM wave in the waveguide can be thought of in terms of the electrons with a fictitious continuous slow wave that propagates along the z-axis [37].…”

Analysis of Ridge-Loaded Folded-Waveguide Slow-Wave Structures for Broadband Traveling-Wave Tubes

“…The validation is carried out for the special case of a /a = 1.0 and b /b = 0.0, which reduces the structure to the conventional serpentine folded-waveguide SWS without ridge loading. The validation of the present quasi-TEM analysis with respect to the Ka-band structure is done against measurements [7], the equivalent circuit analysis, the 3-D CST Microwave Studio simulation, and the parametric analysis (Fig. 3).…”

“…Consequently, there is great interest in the study and development of high-power millimeterwave folded-waveguide traveling-wave tubes (TWTs) [1]- [7]. Analysis leading to the dispersion and interaction impedance characteristics of the structure includes the transmission-line parametric modeling [2]- [6], equivalent circuit analysis [5]- [7], and 3-D electromagnetic modeling [6], [7].…”

“…We then carry out the analysis for the interaction impedance of the structure including the 0018-9383/$26.00 © 2010 IEEE effects of the gap field and space-harmonic effects following the parametric approach used by Hutter [15], Liu [2], and Booske et al [6]. In Section III, the analysis is validated against cold test measurements and full 3-D simulation using CST Microwave Studio (following Booske et al [6]), as well as against the parametric and the equivalent circuit approaches of Booske et al [6] and Sumathy et al [7], respectively. Finally, the analysis is used to study the control of the SWS dispersion by ridge loading for broadband TWTs.…”