High-power Microwave Axisymmetric Mode Antenna Radiation

It is important to study the antenna that can directly radiate cylindrically symmetric modes, which are generated by many high power microwave sources. Two kinds of antenna, Vlasov antenna and COBRA, which are suitable for radiating cylindrically symmetric modes, are investigated through theoretic analyses, numerical calculations and experiments.Theoretically, a series of aspects about the Vlasov antenna and COBRA are studied in detail. Firstly, we research the Vlasov antenna with reflector mainly. A new method to calculate the radiation of the antenna is founded with Vectorial Theory of Diffraction, and the corresponding program is made. The reflective characters of Vlasov antenna are studied with Moment Methods, and the results show that the total reflected energy is less than 0.25%. The radiation patterns of the antenna are analyzed, and the formulas to estimate the wave beam parameters and to design the antenna are provided. The feasibility of radiating high-order modes by Vlasov antenna is also discussed and verified. The hermetization of the Vlasov antenna is researched and the results show that with such kinds of hermetization the antenna can work under gigawatt level. The design of the mode converter from TEM to TMoi is studied, which is useful when the TEM coaxial mode is radiated by Vlasov antenna. At last, the flared-end Vlasov antenna is also discussed. Secondly, we examine the COBRA with segmented parabolic reflectors. The design of the reflector is re-expatiated, which is composed of several equivalent parts of parabolic reflector with the same axis and focus. The radiation formulas are deduced with Current Distribution Methods, and the radiation patterns are calculated. The results show that it can produce high-gain circularly polarized field in the boresight direction (the gain is about 30dBi when the diameter of the reflector is 1.3m) and its 3dB bandwidth is 78%. The radiation formulas of TEM coaxial mode as the radiation mode of COBRA are also deduced. At last, a new folding antenna has been put forward and designed.Experimentally, a Vlasov antenna has been designed and tested at low power. The measured results show that that antenna can work in wide bandwidth (at least from 3.6GHz to 5.6GHz) with gain varying from 19dBi to 23dBi. The measured results agree well withnumerical results, which proves again the validity of our numerical methods.