Research On Wideband Vehicular Antenna With High Gain And Low Elevation Angle Coverage

In this dissertation,a research has been made on the wideband high-gain low-profile vehicular array antennas with low elevation radiation and vertical polarization for applications in mobile base station,spectrum-monitoring systems on vehicle and so on.In the design of these antennas,there are some key technical problems to be solved such as to broaden impedance bandwidth,realize the low profile,to reduce the mutual coupling between the array elements and to reduce the pattern distortion.The main innovative work of the dissertation is summarized as follows:1.Study of wideband wide-coverage sector horn array antenna based on mutual coupling compensation:An E-plane linear array antenna employing sector horns based on mutual coupling compensation is proposed to solve the problem that the strong mutual coupling because of the small element spacing restricts the impedance bandwidth.A relationship of-the mutual coupling compensation is derived from the scattering-matrix analysis of cascaded networks and realized by adjusting the parameters of the feeding structure to achieve a broadband characteristics.The electrical height of the four-element array antenna is 1.14?1(?1 is the wavelength of the lowest operating frequency).Experimental results show that the impedance bandwidth and the average gain of the array antenna are 100%and 10.4dBi,respectively.2.Study of low-profile wideband H-plane rectangular horn based on radiation pattern synthesis:An H-plane rectangular horn mounted on a large metal plate is proposed to meet the requirement of low-profile vehicular antennas.The horn has stable beamwidth in the wide frequency band since multiple modes in the waveguide are utilized to approximately achieve the ideal E-field distribution on the aperture for radiation pattern synthesis.The way of inserting metal pins in the horn is employed to change the weightings of the modes resulting in less H-plane pattern distortion when frequency increases.The electrical height of the horn is 0.17?l.Experimental results show that the impedance bandwidth and the average gain of the array antenna are 106%and 9dBi,respectively.The half-power beamwidth of H-plane radiation pattern is also stable and back-lobe level of E-plane radiation pattern is below-10.7dBi.3.Study of ultra-wideband(UWB)wide-coverage sector horns:In order to meet the requirement of ultra-wideband vehicular antennas,two kinds of ultra-wideband wide-coverage semi-circular sector horns fed by a coaxial probe loaded with a plate are proposed.The feeding structures of a coaxial probe loaded with a rectangular and semi-elliptical plate are adopted to improve the impedance matching at higher frequencies,and the achieved ratios of the impedance bandwidths are 4:1 and 6:1,respectively.The electrical heights of the antennas are 0.21 ?l and 0.18?l,respectively.The measured operating frequency bands are 2.75?11.8GHz and 1.67-10.7GHz covering the UWB band.The measured half-power beamwidth of H-plane radiation patterns are stable and the gains are higher than 3dBi.4.Study of microstrip series-feeding magnetic dipole array antennas:In order to meet the requirement of ultra-low-profile vehicular antennas,two kinds of microstrip series-fed magnetic dipole array antennas are proposed based on the element with low profile,vertical polarization and endfire radiation.The microstrip series-feeding structure is adopted to excite the microstrip magnetic dipoles with a different sizes at different frequencies to achieve wideband and dual-band performances.The electrical heights of the antennas are 0.03?l and 0.017?l,respectively.The measured operating frequency bands are from 5.0?6.7GHz for wideband,from 3.28?3.65GHz and 4.7?5.05GHz for dual-bands.The measured average gains in both cases are higher than 10dBi.