Investigation Of High Power Microwave Radial Line Slot Antenna

With the development of high-power microwave (HPM) technology, innovativeradiation systems which has virtues of co-axis with system, compactness, easyfabrication, light in weight, good acclimatization is badly needed for some specialapplications. Many traditional radiation systems with different structure have beendesigned and come to commercial use successfully in Ku band. However, thepower-handing capacity of this traditional antenna can not meet the requirement of theHPM systems. Only by combining the traditional high frequency antenna technologyand current HPM technology, can a better HPM radiation system be proposed. In thisdissertation, a novel high power radial line slot antenna (RLSA) with low profile isproposed. A unique feature of RLSA is the use of a radial travelling wave for excitationof the slots, which can project circularly polarized electric field and are paired andspirally arrayed on the upper plate so that the radiation is added in phase in the antennabroad side, and the dielectric sheet in the traditional RLSA is replaced by a new radialline slow wave structure. A reflection canceling slot is added to the double-layeredradial line waveguide and the overall antenna return-loss is effectively improved. Thisnovel RLSA is fed by coaxial TEM mode without the mode converter. The detailcontents and innovative work include the followings:1. Optimization of the structure of the radiator unitBecause of the sharp edge of the traditional slot unit of the radial line slot antenna,the power handing capacity can not meet the requirement of the HPM systems. In viewof easy fabrication, good radiation pattern and excellent power handing capacity, a newradiator unit which is composed of two novel slots is studied systematically withtheoretical analyses, numerical simulations, and experimental tests. the simulated powerhanding capacity exceeds1GW.2. Design of a radial line slow wave structureTo suppress the grating lobes from the array, the upper waveguide in the traditionalRLSA is filled with dielectric material and the guide wavelength λgis diminished to ξλ0(λ0is the free-space wavelength), where ξ (<1) is the slow wave factor. However, theappearance of dielectric material in the traditional array antenna leads to the fact that itcan not be used directly into HPM due to the limit of power handing capacity. In thispart, a novel radial line slow wave structure which is composed of a series of concentricannular flakes replaces the traditional dielectric sheet. The simulated results are in good agreement with the numerical analyze ones. At12GHz, the calculated apertureefficiency reaches61.3%.3. Design of a reflection canceling slotThis novel RLSA is fed from a double-layered radial line waveguide to realize thedirectional radiation of high-power microwave. The slots on the top plate are paired,each of which is a unit radiator of circular polarization, and they are arrayed along adesigned spiral so that the radiation is added in phase in the antenna broad side.However, the slots spirally arrayed for circular polarization give rise to serious highorder reflection from the slots, which disturbs the normal antenna operation. As a result,a reflection canceling slot is added to the conventional one, the key technology used inthe design of the novel RLSA, and the antenna return-loss is effectively improved,which is confirmed by simulations, the reflectance is less than0.1, the radiationefficiency is more than99%.4. Fabrication and investigation of the novel HPM RLSAIn this part, a overall novel HPM RLSA is presented and summarized. By assumingthe breakdown threshold to be50MV/m under the vacuum condition, the simulatedpower handing capacity of the RLSA is over1GW. To verify the feasibility of thisnovel RLSA, a experiment should be carried out. However, the Ku-band HPM sourcesare still investigating, a novel RLSA works at9.4GHz was designed, simulated, andtest. The farfield radiation pattern tested is matched well with the simulated one, and thepower handing capacity exceeds1GW, the width of the tested pulse reaches78ns.