Investigations On Circular Polarization Broadband Antennas And Direction Of Arrival

Circularly polarized(CP)antennas can suppress rain and fog interference,reduce multipath reflections,and eliminate polarization mismatch.They are widely used in radar,satellite communications,military,and electronic countermeasures.Modern communications have many requirements for equipment miniaturization and broadband operation,so broadband CP antennas have great application requirements.Direction of Arrival(DOA)can get rid of the beam width,and locate the precise direction of targets.It is widely used in radar,communications,sonar,and other fields.Focusing on broadband CP antennas and DOA,the thesis mainly contains the following research work:1.Based on the Characteristic Mode Analysis(CMA),A broadband microstrip CP antenna was designed.Using CMA,a clock-shaped microstrip antenna with the potential of broadband CP radiation was designed without excitation,and then the optimal feed position was determined according to the minimum difference position of the desired characteristic currents.An improved coplanar waveguide was selected as the feed structure.Finally,the antenna realized CP radiation covering 2.4-3.73 GHz.2.Using the reciprocity of electric and magnetic dipoles,a broadband CP magneto-electric dipole antenna was designed.The antenna contains a pair of horizontal metal patches and a cavity,which are equivalent to an electric dipole and a magnetic dipole in parallel.The profile was reduced from 0.25 to 0.177 by introducing short-circuit walls( corresponds to the maximum operating wavelength).The measured result shows that the antenna achieves a 3d B axial ratio(AR)bandwidth of 67.2%(1.7-3.42 GHz).Besides,the antenna maintains a stable radiation pattern with a gain of 4.2-10.4d Bic over the entire 3d B AR band.3.Based on the substrate integrated waveguide(SIW)technology,a back cavity E-shaped patch CP antenna was designed.The antenna introduces disturbance by setting unequal length slots on the rectangular patch,which makes the symmetrical distribution of the surface current be disturbed and rotate clockwise to realize the left-handed CP radiation.By introducing synapses on the patch,the 3d B AR bandwidth was broaden to 16.5%(41.2-48.6 GHz).The antenna maintains a stable radiation pattern in the boresight direction over the entire operating band.4.Based on the DOA problem of dual-polarization radar array,a new atomic norm was defined,which transforms the DOA estimation problem into the sparse reconstruction problem in the continuous domain.Different from the traditional subspace algorithm,this algorithm is effective for dynamic targets.And,it also overcomes the mesh mismatch problem in the compressed sense method.Simulation results show that the proposed algorithm can significantly improve the DOA estimation performance of dual-polarization array compared with the popular algorithms.