Research On E-band Folded Double-ridged Waveguide Traveling-wave Tube

Space traveling wave tube Amplifiers(TWTAs)are a key stand-alone system in satellite communications and many other space crafts.While TWTAs are widely applied in the last stage of the power amplifier in RF signal links,Space TWT plays a pivotal role in data transfer,as a core component of the TWTAs.As the E-band(71?76GHz and 81?86GHz)is allocated to satellite communications by ITU,Space TWTs in E-band have attracted much attention,especially aiming at next generation satellite communications.In this paper,we present a study of double-ridged folded waveguide(DRFWG)slow wave system(SWS)for E-band TWTs operated at 81?86GHz,which includes theoretical calculations,simulations and experimental testing.The objective of our study is to design a DRFWG for E-band TWTs,which is able to output 80W.Based on the basic theory of the DRFWG,the effect of the main geometry dimensions on the high frequency characteristics was first calculated.Second,CST Microwave Studio was used to simulate and optimize the high frequency characteristics as to obtain the final structural parameters for a designed DRFWG structure.Third,an input and output waveguide transitions were designed,which consists of a rectilinear ridge waveguide and a tapered waveguide.Compared with conventional folded waveguides,the DRFWG SWS is more complex.It is found that the VSWR of the entire DRFWG structure designed is below 1.45 within the operating bandwidth.Next,PIC simulation of beam-wave interaction was conducted,showing the E-band TWT was able to achieve an output power 139W,electron efficiency 6.2%and the saturated gain 41.0dB at a center frequency of 83.5GHz.All these three data meet the initial design requirements:output power114W,electron efficiency 5.06%and the saturated gain 40.0dB in the operation bandwidth.Finally,the DRFWG SWS was fabricated,which will be also presented in this paper.The whole component of the SWS was divided into three parts for the machining by the CNC technique.The finished parts were subject to surface cleaning,pickling and processing accuracy tests.The vector network analyzer was used to test VSWR that was below 1.55,verifying the reasonable transmission characteristics of the structure.