Study On Dual-Mode Resonant Low-Profile Vehicular Antennas

With the growing of the Internet of Vehicles,the demand for low-profile directional vehicular antennas is increasing.However,existing directional vehicular antennas are difficult to achieve both low-profile and wideband characteristics at the same time.Therefore,this thesis is devoted to the design method of the dual-mode resonant backfire antenna.A mode synthesis design method based on the eigenmode theory is proposed.By simultaneously exciting multiple resonant modes in the circular sector patch,a general design method of low-profile dual-mode resonant backfire antennas is formed.A series of backfire antennas with different performance that meet the needs of vehicular applications are studied and realized.The main content of this thesis includes:1.According to the mode mapping relationship between the magnetic dipole and the circular sector patch antenna,the mode synthesis table for regulating the resonant mode order of the circular sector patch antenna is obtained,and the radiation characteristic formulas are derived.It is found that the backfire radiation characteristic can be realized by exciting the first two odd-order resonant modes.By introducing the multi-point equivalent source model,the working mechanism of dual-mode resonant backfire enhancement characteristics is analyzed quantitatively.2.By deducing the conditions for realizing the dual-resonant backfire radiation enhancement characteristic in the circular sector patch antenna: The length must be double wavelength and the flared angle must between 180° and 360°.A 360° circular sector patch antenna is designed and fabricated for validation.It is verified that the proposed antenna achieves dual-resonant backfire characteristic from 4.72 GHz to 6.14 GHz,and the backfire gain increases from the value below-3.5 d Bi to about-0.5 d Bi.3.In order to further enhance the backfire radiation characteristic,the closed-form radiation formulas of the circular sector patch antenna at different flared angles are studied.The flared angle is determined to be 180° for the maximum backfired gain.In addition,a multi-point equivalent source model is introduced to analyze the size and position of the reflector and the director,which can fully enhance the backfire radiation enhancement characteristic.A 180° circular sector patch vehicular antenna with a reflector and a director was designed and fabricated.It is evidently validated that the proposed approach can be employed to effectively enhance the backfire radiation of low-profile vehicular antennas and the backfire gain can reach 4.2 d Bi.4.The factors affecting the sidelobe level within xy-plane are studied in detail.The relationships between sidelobe level and frequency,the shape of reflector and the shape of director are revealed.A triple-element antenna with a rectangular reflector and a rectangular director is designed and fabricated,which can effectively suppress sidelobe level.A series of planar antennas with the profile height close to 0.037-wavelength and the bandwidth greater than 26.2% are realized in the above research work,which can cover DSRC 5.9 GHz band.The gain parallel to the vehicle is about 7.7 d B higher than that of the conventional patch antenna and the backfire gain reach up to 4.2 d Bi,which can meet the requirements of vehicular applications.