Study On Vehicular Patch Antennas With High Gain And Low Side-Lobe Level Under Triple-Mode Resonance

The new generation of mobile communication carries development opportunities for the Internet of Vehicles technology,and the demand for high-gain directional vehicular antennas has also dramatically increased.However,it is always challenged to enhance the radiation level in the direction parallel to the metallic vehicle body while simultaneously maintaining low side-lobe level.Therefore,this thesis is devoted to the design method of the high-gain and low side-lobe level vehicular antenna.Based on the theory of multi-mode resonance and the principle of microstrip YagiUda antenna,a design method of the triple-resonant,high-gain and low side-lobe level vehicular antenna is proposed.A series of directional antennas with different characteristics are studied.The main work of this thesis includes:1.The radiation characteristics of sector patch antenna and multi-mode resonance theory are extended to the design of triple-mode resonant sector patch antenna.The radiation characteristics of the sector patch antenna with different flared angles are studied.It is found that the first three oddorder resonant modes can be excited to realize the backfire radiation characteristic when the flared angle is appropriate.According to the principle of microstrip Yagi-Uda antenna,a reflector is introduced to enhance the backfire radiation characteristic.In addition,a six-point equivalent source model is established to quantitatively analyze the working mechanism of triple-mode resonance low side-lobe backfire enhancement characteristics.2.Based on the above theory,when the flared angle of sector principal radiator is 240°,the antenna shows strong backfire characteristic and the higher-order modes are effectively suppressed.Then,a six-source equivalent source model is established to analyze the size and position of the reflector,as well as the coupling relationship between the reflector and the principal radiator.By using the six-source model,it is found that the backfire radiation can be fully enhanced when the coupling relationship between the reflector and the principal radiator is electrical.An antenna with a 240°circular sector patch,a reflector width of 1/4-wavelength and a center frequency of 5.5 GHz is designed and fabricated.It is verified that the proposed antenna achieves triple-mode resonance low side-lobe backfire enhancement characteristics from 3.7 GHz to 6.2 GHz,the backfire gain can reach5.6 d Bi,and the first side-lobe level is lower than-12.5 d B.3.In order to further enhance the backfire radiation and reduce the first side-lobe level,the influence of the reflector width on the radiation characteristics of the antenna are studied.An antenna with reflector width of 3/4-wavelength is designed for verification.The backfire gain of the proposed antenna can be increased from 5.6 d Bi to about 7.3 d Bi,and the first side-lobe level can be reduced from-12.5 d B to-16.4 d B.4.The factors affecting the backfire gain within xy-plane are studied deeply and the influence of the substrate on the radiation characteristics of antenna is revealed.An antenna is designed on the substrate with dielectric constant of 2.65 and thickness of 2 mm.It is verified that the endfire gain of the proposed antenna can reach 4.1 d Bi and the impedance bandwidth is 18.0%.