Design Of Dual-port Monopulse Antenna With High Isolation And Dual-band Wide-beam Circularly Polarized Antenna

The research works are made on the basis of scientific research projects.And the major research can be divided into two parts: The first part is the design of a dual-port monopulse antenna with high port-isolation.And the second part mainly focuses on the design process of a dual-band wide-beam circularly polarized antenna.The main contexts of the dissertation are outlined as follows:1.Design of the dual-port monopulse antenna with high port-isolationConsidering to the application scenes of monopulse antennas,the basic theories of target-detection and the current research state of monopulse antennas are introduced.On the basis of previous researches,the constrains like complicated feeding network and port-isolation are discussed.Furthermore,a simple dual-port monopulse antenna with high port-isolation is presented.The propose antenna is simulated using ANSYS HFSS,fabrication and measurements are carried out to validate the design.Measured results show that the antenna has a return loss less than-10 dB in the operating band.And port-isolation better than 50 dB is achieved in a wide band.Additionally,the antenna can produce a sum beam and a difference beam,in which case the antenna can be used in monopulse radar system to realize target detection.2.Design of dual-band wide-beam circularly polarized antennaAccording to the requirements of BeiDou satellite navigation system,relative concepts and current research state of wide-beam circularly polarized antennas are introduced firstly,and the difficulties to realize the characteristics of dual-band and circular polarization operation in a limited compact size are pointed out.In the end,the corresponding solutions are proposed including the design of the antenna and its feeding network.A quadrifilar helix antenna with two parallel radiation arms is proposed to realize the dual-band and circular polarization characteristics.Accordingly,a feeding network comprised of two stacked Wilkinson power dividers is designed to minimize the overall size.According to the simulation,the voltage standing wave ratio(VSWR)of the antenna is less than 1.92 in the whole operating band,and the 90°elevation gain is better than 4.5 dBic,the 90°~45°elevation gain is better than 1.8dBic.Meanwhile,the axial ratio(AR)along the +z axis is less than 3 dB.Simulated results prove that the antenna has a good performance of wide-beam and circular polarization,which makes it applicable for engineering.