Estimation of RF-wall loss in slow-wave structures for traveling-wave tubes

Return-loss resonance method is used to estimate the loss per unit length of two different slow-wave structures namely a tapered ferruled coupled-cavity structure operating at centimeter-wave band and a ferrule-less folded-waveguide structure operating at millimeter-wave band. The loss estimated by this method was found to be within 2.5% and 5% compared against those obtained using conventional transmission loss method (S21 value) and numerical simulation carried out using CST-Studio. This approach was found to be very simple yet reasonable accurate to estimate the loss of the periodic structures operating in cm- and mm-wave bands.