Study On Low Profile Electro-magnetic Complementary Dipole Antenna

This thesis is devoted to the design method of low profile antenna.Through the discussion of the basic principle of electro-magnetic complementary antenna,the necessary conditions for directional radiation are studied.Based on the most basic loop-dipole combined antenna,this thesis discusses the methods to reduce the profile of linearly polarized and circularly polarized complementary dipole antennas,while maintaining their unidirectional characteristic.The main contents of this thesis include:1.Based on Huygens source theory and even-mode resonant loop theory,the condition of directional radiation produced by the combination of half-wave dipole and even-mode loop is strictly proved,that is,the excitation with the same amplitude and 90° phase difference is provided.The rule of directional radiation produced by the combination of magnetic dipole and electric dipole is revealed,the correctness of Huygens theory is proved.2.Based on the formula of radiation characteristic of loop and dipole,the method of reducing the profile of antenna to one eighth-wavelength is realized theoretically through further derivation of the formula of loop-dipole combined antenna.The method of "bending feed line" is explored to reduce the profile of antenna.A novel low profile loop-dipole combined antenna is designed and fabricated.The operating frequency of the antenna is 2.5 GHz,the height of the profile is 0.125-wavelength.The results show that the design method can effectively reduce the profile of the antenna and maintain good directional performance.Meanwhile,in order to further study the influence of feeder to the antenna's performance,a combined loop-dipole antenna with fork-like stubs feeding is designed and fabricated.By diagonally exciting the non-uniform loop,it is found that the circular polarization can be produced.3.According to the above research,the idea of reducing antenna's profile is extended to circularly polarized antenna.In order to solve the problem that it is difficult to realize low profile characteristic for the loop-dipole combined directional circular polarization antenna,referring to the excellent directionality of Yagi antenna,a combined antenna model with a director element is simulated by using software.Then the parameters of the antenna are optimized.After that,a low profile antenna with an operating frequency of 2.5 GHz and a profile height of only 0.09-wavelength is designed and fabricated with the optimal size circularly polarized loop-dipole combined antenna.The outstanding advantage is that the dipole is used as the launcher,a small loop is added above the loop as the director,which realizes the excellent characteristics of low-profile and directional circular polarization.According to the above theory and results,it can be concluded that the method of bending feed line and the approach of adding director element can effectively shrink the profile of loop-dipole combined antenna,these two ways can be used in the miniaturization design of various combination antennas in the future.