Design And Optimization Of Planar Array Antenna

With the rapid development of wireless communication systems,planar antenna is popular with its advantages of low profile,high gain,and miniaturization.As a kind of planar antenna,the waveguide slot antenna is the mainstream trend.Such kind of antenna has a compact structure,high radiation efficiency,and is easy to achieve low sidelobe and low crosspolarization characteristics,which is widely used in airborne Fire control radar,mobile satellite communication system,vehicle collision avoidance radar and weather radar.Substrate integrated waveguide(SIW)is an evolution of traditional metal waveguide.It has similar transmission characteristics to traditional ones.It is light in weight,low in manufacturing cost,and easy to integrate with planar circuits,which further broadens the application range of waveguide-like planar array antennas.Based on the application in radar field,this thesis focuses on ridge waveguide slot array antennas and SIW slot array antenna with 45° linear polarization.The major work of this thesis includes the following parts:Firstly,the design method of the X-band miniaturized ridge waveguide slot array antenna is studied in this thesis.The cross-sectional size of the standard waveguide is too large to meet the array spacing requirements of the phased array for large-angle scanning.This thesis uses the finite element method to accurately calculate the cut-off wavelength based on the transmission phase of the ridge waveguide.Under the condition of ensuring good transmission and radiation characteristics,the cross-sectional area of the ridge waveguide is reduced to 41.1% of the standard waveguide in the same frequency band.Then,a miniaturized ridge waveguide slot array antenna with low sidelobe characteristics is designed in this thesis.Taking the coupling among the slots into consideration,the conductance and slot parameters of the wide-side bias slot of the ridge waveguide are extracted based on the 8-slot sub-array.Two important curves of conductance-resonance length and resonant length-offset distance of the radiation slot are established by curve fitting method,and then a preliminary ridge waveguide slot antenna simulation model is established based on the theoretical conductance distribution curve.Besides,several optimization methods for the sidelobe level of the waveguide slot array antenna are listed,and the sidelobe level is optimized by the near-field approximation method.For the practical test,a ridge waveguide-to-coax transition and a matching load are designed.Finally,the X-band ridge waveguide slot array antenna has been fabricated and measured,and the measured and simulated results are in good agreement.Lastly,this thesis also designs a low sidelobe SIW slot array antenna with 45° linear polarization.The radiating element of this antenna is a pair of slots consisting of two oblique45° rectangular slots with different length,which are equivalent to capacitive and inductive loads,respectively.By selecting the appropriate length of the slots based on the extracted parameters of the slot,the slots spacing one-half the wavelength can be excited approximately in phase,thereby radiating 45°-inclined linear polarization.On the basis of the 45°-inclined SIW slot array antenna with constant amplitude excitation,the tapered distribution of the excitation amplitude of the linear array is realized by controlling the axial displacement of the inductive oblique slot,so as to realize the low sidelobe 45° linear polarization SIW slot array antenna.The simulation results show that the final designed 8×1645° linearly polarized SIW planar array antenna working in the millimeter wave band has the sidelobe less than-25 d B and the aperture utilization rate up to 73.9%.