Study On The Rectangular Helix Traveling Wave Tube

Traveling wave tube (TWT) is the most classical type of microwave vacuum tube. It has been frequently used as millimeter wave radar, guidance, tactical and strategic communication, electronic countermeasure, remote sense, radiation measurement and so on. Its performance directly influences the level of the weapon equipments. With the development of the mordern electronic wars and space applications, there is great requirement of a large amount of compact TWTs with wider bandwidth, higher gain, lighter weight, smaller size. Recently there is an increasing interest in the study on new slow-wave structures(SWS) of TWTs for potential applications in phase array antennas, microwave relay system, and coaxial tv cables. Yet the conventional TWTs can not meet the requirs for theirs high cost, bulky volume, low efficiency. Sheet electron beam have lots of attractive virtues, For example, Sheet electron beam could greatly decrease the space charge force that might reduce the focusing requirement; when it was used in microwave tubes, it can carry higher currents than those with solid beams, so these virtues have attactted interests of the vaccum tubes reseachers greatly. At the same time compatible with MEMS techniques.the fabrication technique increasing reliability, improved repeatability and small tolerance is necessary. Fortunately, the micro-electro-mechanical systems (MEMS) can meet these requirements, which results in innovative TWT designs based on this technology. Thus, the investigation on the novel compact slow-wave interaction structures based upon MEMS technique is more important. And it has importantly realistic significance for the study on the new type of compact traveling wave amplifiers. In this dissertation, we have made detailed theoretical and experimental study on the rectangular helix slow wave structures. Several important and valuable results which bring forth new ideas are achieved and listed as the following:1. For the first time, the theory of a free helix system with rectangular cross section is presented. With the Sheath model, by using the modified field-matching method and the integral boundary conditions, the dispersion equations and the coupling impedance of this structure are obtained. The dispersion equations consider the influence of the width of the cross section. After the analysis, the differences of this theory with the approximately theory are compared, also the theory data are compared with the HFSS data, moreover, the effects of the physical dimensions on the dispersion characteristics and the coupling impedance are obtained. We derive that the approximately theory is limited in the structure of the ratio of width to height is big, and the width of the sutucture effects on the dispersion property and the coupling impedance greatly.2. In order to compare the slow wave property of the rectangular structure with that of the traditional circular helix, we analyses several circlular helix structures. Then we obtained the dimensions of the circular helix structure which has the equivalent dispersion property with the rectangular helix. Also we realize the rectangular helix has some advantages over the equivalent circular helix.3. The introduction of the normal rectangular helix and the inverted rectangular helix structures incorporating metal shields is shown. A modified field-matching theory of this strctures printed on dilelectric substrates is obtained using the electromagnetic integral equations at the boundaries. And theoretical results are compared with the HFSS's simulation data, they accord with each other, which means that the theory which we put forward is accurate to analyze the printed rectangular helix structure. Theoretically, we have analyzed the effect of the dielectric on the properties of the structure. Then we compared the slow wave properties of the free rectangular helix, the normal rectangular helix and the inverted rectangular helix with the same geometry dimension.4. The hot dispersion equations of the rectangular helix slow wave structure with a sheet electron beam which has the same cross section with the rectangular helix is obtained according to self-consistent field theory. And the small signal gain per period of the rectangular helix is also derived. Based on the theory, the effect of the structures parameters and the beam paremeters on small signal gain per period of the structures is investigated by numerical calculation. Meanwhile, the small signal gain per period of the rectangular helix is compared with the equivalent circular helix.5. Referring to Tien's one-dimensional disc model, we put forward one-dimensional rectangle model within rectangular helix structure. On the basis of equivalent circuit, the equations describing the large-signal operation of the rectangular helix traveling-wave amplifier are derived, then, the charge of high frequency voltage and electronic phase along longitudinal direction, and parameters such as saturation gain and interaction efficiency are discussed.6. Using resonance method, we have made experiments on the dispersion of an inverted rectangular helix slow wave structure, and the experimental results are in good agreement with the theoretical data.