Vane-loaded Helix Slow-wave Systematic Experimental Study

In this dissertation the main form of slow-wave circuit in design of broad-band TWTs, namely, vane-loaded helical SWSs (slow-wave structures) are studied by experiment and computer simulation. An experiment installation is setup to measure cold parameters of helical SWS with Agilent Vector Network Analysizer on the basis of analysizing methods for measuring dispersion and interaction impedance of helical SWSs. In order to remove reflection effects, the measurement system is represented by proper microwave network, and the formula for modification of the phase shift△φ is derived. The same method is used in measure of attenuation to modifytransmission parameter S|â†'₂₁, . Taking high order space harmonic into account, thedispersion and interaction impedance are simulated by HFSS. The results show that high order space harmonic has no prominent effect on interaction impedance. Results obtained by computer simulation and experiment have excellent consistency with each other. Several important and creative results are achieved and listed as follows.1. Methods for measuring dispersion and interaction impedance are analysized. The resonant and nonresonant perturbation theories are deduced in detail. The former is often used in computer simulation, however, the latter in experiments because it is not easy to make up a resonant helical SWS. Similarly, because it is difficult to find a slender and strong dielectric rod, slim metal wires are used as perturbers in the measurements of interaction impedance.2 An experiment installation with Agilent Vector Network Analysizer is machined and setup to measure cold parameters of helical SWS. Dispersion and interaction impedance of several helical SWS with and without metal vanes are measured. In order to remove reflection effects of the input and output transformers of the measurement system, a proper microwave network is introduced and transmission matrices are used to derive a formula for modification of the experimental values ofphase shift △φ, which can effectively damp the fluctuation of △φ. Besides, the same...