Optimization Of A Cavity With Multimode High-Q TE_01P Of Cylindrical Cavity Mode Purification

Microwave equipments are indispensable in the field of satellite communicationsystems, stealth technology etc, the performance of those equipments is closely relatedto the dielectrical properties of material. Therefore, different test systems play animportant role in obtaining the complex permittivity of the dielectric materialaccurately.On the basis of the cylindrical cavity theory and national standard GB/T5597-1999which content is about high-Q cavity method, we optimize the high-Q cavity whichfrequency band covers18～40GHz. Purify TE01pmodes and eliminate interferentialmodes. The resonant frequency of interferential modes are closed to the TE01pmodes orsame as TE01pmodes, just like the degenerate modes TM11p. The purpose of optimizingthe structure of cylindrical cavity is to eliminate the interferential modes and ensure theaccuracy of the measurement.The main research work is as follows:1. Optimization of the structure and size of the high-Q cavityThe high-Q cavity consists of main cavity, piston and rear cavity. Coupling holesopen in the sidewall of the cavity. The resonant frequency of the TE01pmodes isdetermined by size of the main cavity. Optimize the size of the main cavity can excludemost of the non-degenerate interferential modes. Piston is not in contact with the wall ofthe main cavity, this structure can cut longitudinal current of TM11pmodes. Absorbingmaterial which put into the rear cavity can absorb the energy of TM11pmodes.Optimize the size of the main cavity by resonator mode chart. With the help ofsimulation software HFSS, optimize the size of the piston and the rear cavity, theparameters of the absorbing material, the position and the size of the coupling device.The data after optimizing is as follow:The diameter of main cavity is22.xx mm, the length of that is30.xx mm. The gapbetween piston and main cavity is0.6mm, the height of piston is1.5mm. The diameterof the first step of the rear cavity is16.65mm, the height of that is3mm. The diameterof the second step of the rear cavity is12.0mm, the height of that is4.1mm. The ε’ of the absorbing material is6.7, the tanδ of that is0.5. Processing the cavity according to thesedata.2. Test the optimized high-Q cavity from18to40GHzFirst, the new high-Q cavity is tested repeatedly without sample.We compare thequality factor of the new one with the old one.Then, the sapphire sample is measured bythe system from18to40GHz. Finally, the test data is analyzed.The results show that the optimization is reasonable. The test system satisfies thedesign indices and the demand of the test error.