Research On VHF/UHF Antenna Array

With the rapid development of wireless communication systems and technologies,there is increasing demands on the performances of communication antennas such as bandwidth,gain,and directionality in military and civilian fields.It is particularly important that the antenna provides good electrical performance in a complex electromagnetic environment.This thesis focuses on the array elements to achieve high-efficiency,miniaturization,and low-profile,as well as the beamforming technology of the corresponding circular array in VHF/UHF.The thesis proposes three feasible array elements and does in-depth researches.Firstly,an improved dipole antenna is presented.The bandwidth of the antenna is broadened significantly thanks to the combination of a tapered connection surface and electromagnetic coupling feeding method.The improved broadband dipole antenna has wide bandwidth and omnidirectional radiation patterns in the horizontal plane.Secondly,a low-profile monopole antenna is investigated,which obtains wide bandwidth by combining the inverted cone feeding structure with the coupling feed mechanism.The low profile characteristic of the antenna is also achieved by adding the loading capacitance and shorting pins.The profile of the antenna is approximately 1/10 free space wavelengths at the low frequency point.Finally,a wideband sleeve antenna is studied.The height of the antenna is effectively reduced by the top loading.The gradual change of the outer sleeve ensures the broad bandwidth of the antenna.The antenna presents good impedance matching performance with VSWR<2 within the whole frequency band,moreover,the antenna achieves uniform omnidirectional radiation patterns with a lower than 0.27 d B gain variation and a gain of higher than 1.3 d Bi in the horizontal plane.Furthermore,the beamforming technology of an uniform circular array in VHF/UHF is also investigated based on the aforementioned sleeve antenna.The array antenna obtains good gain characteristics as well as the directionally adjustable beams in the horizontal plane by optimizing array elements' amplitude and phase distribution and the diameter of the circular array.