This paper presents a new problem on the filter properties of the axial conductor loaded helix. By using the equivalent transmission network analysis

it shows that the filter properties are different from those of the structures as suggested in narrow band TWT. In this kind of structure

the TWT can be constructed not only in narrow band operation

but also can be constructed in super-wide band operation.The theoretical analysis of the axial conductor loaded helix shows that its transverse impedance can be loaded lower enough even to 50 ohms and easy matched to the external coaxial coupler directly

while at the same time

it still maintains the coupling impedance in rather higher values and obtains high gain in TWT.The one of the distinguished advantage of the filter type slow wave circuit using in TWT is its property of suppression the BWO. Axial conductor loaded helix also has such kind of property. Dr. Otto Sauseng of USA in 1970 had adopted this kind of slow wave circuit in his TWT

no BWO occured

yet he gave no explaination. Actually

as shown in this paper

the suppression of BWO is due to the filter property of the structure. The TWT when using this kind of structure shows that the operation is quite stable. The theoretical calculation method of the axial conductor loaded helix as used in USA is the S. F. Paik’s method

while in USSR the H. H. method is used. But these two methods mainly gave out the dispersion relations

no filter properties were pointed out

and no such kind of characteristics as the pass-band

the stop band

the suppression of BWO

the effect of the numbers of metalic conductor

the effect of the dimensions of the metalic conductor

and the effect of the position of the coaxial coupler

were revealed out. While in this paper

all these problems are analyzed and relations are given. Besides

the cold circuit experiment has been performed and the dispersion curve obtained is shown more close in this method than in S. F. Paik’s method

and the match of the input coupler in super-wide band is also quite well. Therefore this filter analyzing method can be used to design such kind of loaded helix for super-wide band TWT.