Research On High Performance Broadband Omnidirectional Antenna

Omnidirectional antennas can achieve omnidirectional radiation in a specific plane,so they are widely used in military communications,radio and television,radio frequency identification,mobile communications,indoor communications,wireless sensing and other fields.With the rapid development of modern wireless communication systems,people put forward more and more stringent requirements for high-speed transmission of large-scale digital information,so the design index of omnidirectional antennas will become more and more challenging.Combined with application background and technical requirements,this thesis designs and analyzes four high-performance omnidirectional antennas.The main contents of this thesis are as follows:1.A broadband monopole antenna based on coupling feeding is designed.The main structure of the antenna is printed on the dielectric substrate.By deforming the structure of the coupling feeding planar monopole antenna,and introducing top-loading disc and long branches,miniaturization and broadband of antennas are realized.The size of the antenna is0.072λ₁×0.031λ₁×0.146λ₁（λ₁is the wavelength corresponding to the lowest frequency）.The simulation results show that the VSWR of the antenna in the working frequency band is less than 3,the relative bandwidth of 115%is achieved,the horizontal gain is greater than-2.5d Bi,and the omnidirectional gain variation is less than 3d B.For fabrication and far-field test of the antenna,the actual measurement results show that the antenna simulation and tested VSWR are consistent,the tested average receiving level is higher than that of the comparison antenna,and the omnidirectional gain variation is less than 3d B.2.A broadband miniaturized planar monopole antenna is proposed.The antenna is deformed by the dielectric substrate structure of the above-mentioned coupled-feed broadband monopole antenna.On the basis of ensuring the original impedance bandwidth,Introducing a new dielectric substrate and loading open and short stubs to achieve planarization and miniaturization of the antenna.A reduced size of the antenna is 0.065λ₁×0.031λ₁×0.131λ₁.The simulation results show that the VSWR of the antenna in the frequency band is less than3,the relative bandwidth of 115%is achieved,the horizontal gain is greater than-5.7d Bi,and the omnidirectional gain variation is less than 3d B.The actual measurement results show that the trend of antenna simulation and the tested VSWR are consistent,the tested average receiving level is higher than that of the compared antenna,and the omnidirectional gain variation is less than 3d B.3.A horizontally polarized circular array filter antenna is designed.Based on the theory of small electric length loop antenna,it uses a broadband antenna unit,an interdigital filter and a power divider to form a four-element feed ring array.Therefore,the antenna has horizontally polarized omnidirectional and filtering characteristics.Only a single port can feed the antenna.The size of the antenna is 0.5λ₁×0.5λ₁×0.006λ₁,and the simulation shows that the antenna achieves a relative bandwidth of 25.2%in the working frequency band,the omnidirectional gain variation is less than 3d B,the average gain in the horizontal direction is between 0-1.7d Bi,and the beam width in the vertical direction is greater than 100°.The actual measurement shows that the antenna achieves a relative bandwidth of 26.8%,the omnidirectional gain variation is slightly greater than 3d B,the in-band horizontal gain is between-0.24-1.58d Bi,and the vertical beam width is greater than 100°.4.A low-profile broadband antenna with oblique radiation and vertical polarization is proposed.Based on the design idea of oblique radiation and vertical polarization,a miniaturized antenna unit and a power divider are designed to form a four-element circular array antenna.The size of the antenna is 0.788λ₀×0.788λ₀×0.018λ₀（λ₀is the wavelength corresponding to the center frequency）,the relative bandwidth of 19.1%is achieved in the frequency band,the omnidirectional gain variation is less than 3d B,the oblique gain is greater than 5.5d Bi,and the vertical beamwidth is greater than 24°.The size of the horizontally composed 2×2 MIMO array antenna is 1.907λ₀×1.907λ₀×0.018λ₀,which achieves a relative bandwidth of 18%within the frequency band,the isolation is less than 20d B,and the ECC is less than 0.01.The two antennas are fabricated and tested.Compared with the simulation,the curve trends of the VSWR,unit isolation,ECC and main polarized gain of the antenna test are consistent.