Novel slow-wave structure for high voltage TWTs

Pchelnikov, Yuriy N.; Vlasov, Alexander N.

doi:10.1109/ivec.2012.6262160

Cited by 5 publications

(4 citation statements)

References 2 publications

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“…This limits the bandwidth of the contrawound and ring-bar SWSs to just 10% -20% [4]; but the backward wave interaction is greatly reduced. Very recently, a ring-based circular SWS ( Figure 2.7(c)) consisting of two circular helices connected by circular rings has also been proposed to operate at high frequencies and beam voltages without backward wave oscillation [43].…”

Section: Variations Of Circular Helixmentioning

confidence: 99%

“…For instance, the cross-wound helix [26] and its practical version, ring-bar structure [41], have been proposed to improve the traveling-wave tube (TWT) amplifier operation at high power levels. Coaxial contra-wound circular helices of different radii have been proposed to couple input and output power in a TWT [42]- [43]. Very recently, a structure consisting of two circular helices connected by circular rings has been proposed to increase the operating frequency and output power of TWTs [43].…”

Section: Introductionmentioning

confidence: 99%

“…Coaxial contra-wound circular helices of different radii have been proposed to couple input and output power in a TWT [42]- [43]. Very recently, a structure consisting of two circular helices connected by circular rings has been proposed to increase the operating frequency and output power of TWTs [43].…”

Section: Introductionmentioning

confidence: 99%

“…circular helices connected with circular rings; compared to a single circular helix, this structure is able to operate at higher frequencies and higher voltage levels with a larger electron beam tunnel and lower risk of backward wave oscillation. The connected pair of PH-SECs realizes the circular structure of[43] in a planar form so that it can be fabricated using printed circuit or microfabrication techniques.In this section, we present proof-of-concept design and fabrication of the connected pair of PH-SECs using printed circuit techniques.…”

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confidence: 99%

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Planar helix-based slow-wave structures for millimeter wave traveling-wave tubes

Zhao¹

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Circular helix is a very popular slow-wave structure (SWS) for application in traveling-wave tubes (TWTs). But it is not easy to be fabricated using printed-circuit or microfabrication techniques which are important for low-cost fabrication and high frequency applications. In this context, during the last few years, a planar helix SWS with straight-edge connections (PH-SEC) has been proposed and studied. Unlike the circular helix, the PH-SEC is suitable to be fabricated using printed circuit or microfabrication techniques. However, there are still some issues and problems that need to be addressed for the PH-SEC when used in millimeter wave TWTs. First of all, there can be backward wave oscillations when the TWT is working at high voltages. Secondly, the size of the SWS, the electron beam tunnel, and the beam get very small, causing difficulty in fabrication, alignment, and focusing of the electron beam. Thirdly, at millimeter wave frequencies, it is more likely that the electrons hit the supporting dielectric, causing dielectric charging which will affect the performance of the TWT adversely. Moreover, PH-SEC can be dispersive in the presence of dielectric loading, reducing the bandwidth of operation. This thesis presents novel SWSs which are based on the PH-SEC and solve some of these problems. First of all, two types of coupled planar helices, an unconnected pair of PH-SECs and a coaxial pair of PH-SECs, are proposed. Their dispersion characteristics are derived from analysis based on field-theory. The characteristic equations and field expressions are obtained to explain the nature of different modes that propagate in the coupled structures. Coupling impedance is also calculated. Effects of variations in dimensions are studied. The analysis results match well with simulations. Simulation results are presented to show that the unconnected pair of planar helices has a reduced interaction with backward waves as compared to that for a corresponding single PH-SEC. Based on the above knowledge of various modes, an unconnected pair of PH-SECs has been designed together with a stripline power divider in order to provide input signals with equal magnitude and phase. Also proposed is a connected pair of PHvi SECs which can be fed in a much simpler way by a coplanar waveguide (CPW) feed. The latter structure offers a larger electron-beam tunnel and lower risk of backward wave oscillation compared to the single PH-SEC. Moreover, the connected pair of PH-SECs has a higher gain growth rate than that for the single PH-SEC. The connected pair also shows a significantly higher coupling impedance compared to a recently reported meander-line based SWS. Both the unconnected and the connected pair of PH-SECs have been designed and fabricated using printed circuit techniques. The measurement results match well with the simulation results.

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Section: Variations Of Circular Helixmentioning

confidence: 99%