Research On Ultra-Wideband Spiral Antenna

With the rapid development of wireless communication technology,the performance of wireless communication system,such as radar systems,anti-jamming systems,terminal communication systems,is improved continuously,so the requirements for the design of antennas at the transmitter and receiver are becoming more and more demanding.In this thesis,the power beamwidth,the axial ratio beamwidth and the efficiency of the ultra-wideband spiral antenna are been explored and studied.Firstly,the theory of the spiral antenna is been expounded,including the classification,the radiation characteristics,the frequency bandwidth and the impedance characteristics.Then,the performance of the planar and the conical spiral antenna loaded with a reflective cavity is compared under the same size condition,and the conical spiral antenna has advantages of the wider power beamwidth and the higher efficiency.Based on the original structure,two conical spiral arms are been bent and wrapped by loading the sine function to extend the path of the radiated current,which could improve the axial ratio characteristics in the high frequency band.Loaded a small metallic plate above the reflective cavity,the electromagnetic energy radiated downward can be reflected in the high frequency band.As a result,the axis ratio is been further decreased and the radiation efficiency is significantly improved in the high frequency band.The representative exponentially tapered micro-strip balun is been analyzed and the open transmission structure has the problem of electromagnetic energy leakage,which has a little impact on the axial ratio in the z-direction,however,results in a significant decrease of the axial ratio beamwidth.In this design,the transverse dimensions of the blaun are reduced,which can alleviate the problem of the energy leakage.In order to simulate the carrier platform of the conical spiral antenna,a large metallic ground is added underneath,and the reason of the performance deterioration caused by the ground is analyzed.Placing a ring-shaped absorbing material above the ground could reduce the influence of the large ground.At last,0d B power beamwidth and 4d B axial ratio beamwidth of the designed conical spiral antenna both achieve 100° in the operating band of 6～18GH,with the diameter of 25 mm and the profile of 14 mm.Finally,the proposed conical spiral antenna was fabricated and measured,and the measured and simulated results were compared and summarized.