Study On Reconfigurable Airborne Short Wave Antenna Similar To Folded Monopole

The development of shortwave radio communication has a long history and excellent performance including long-range detection,strong survivability and no relay.Due to the special working environment of airborne shortwave antenna,it must meet the requirement of achieving higher gain and smaller size and weight in the working band.However,in low-band HF,the extremely low resistance of the traditional airborne shortwave antenna leads to tuning difficulties in partial frequency,high loss of matching network and low total efficiency of the antenna system.Using the reconfigurable antenna technology to make the airborne antenna has a variable electrical characteristics,which not only can reduce the size of the airborne equipment,but also improve the performance of the antenna system etc.The loop antenna is one form of airborne shortwave antenna located at the leading edge of the the vertical stabilizer with composite material and does not damage the aerodynamic performance of the aircraft.The design of airborne shortwave antenna requirements antenna size can not exceed 0.5m×0.5m×3m,the working bandwidth to be covered 2~30MHz,the VSWR is substantially smaller than 1.5 after tuning and gain as large as possible.In all cases when the aircraft is taking off,landing and in flight,in order to ensure reliable communications,the antenna pattern should not have deep blind spots on the flight path,and the horizontal pattern should be omnidirectional.A novel method is proposed in this thesis to improve the performance of shortwave loop antennas by reconfigurable antenna technology and folded monopole theory.And the reconfigurable airborne short wave antenna based on traditional airborne short wave loop antenna is designed.Based on the simulation of Ansoft HFSS and ADS,the impedance matching and efficiency of the antenna system are analyzed and greatly enhanced.The performance improvement of the reconfigurable shortwave antenna is verified by the results of test and this kind antenna meet the requirements to achieve remote high-quality communication on aeroplane.According to the the traditional airborne shortwave antenna and based on the folded monopole theory to analyze the antenna current and input impedance,we optimize it step-by-step by conduction bands loading and antenna reconfiguration.We loads specific conduction bands between the vertical conductor plates of the traditional loop antenna in order to change the current distribution.By means of changing the configurations of the switches to change the position and the number of the conduction bands at different frequency,then the transmission-line mode is resonant and the antenna mode mainly produces radiation power.It will increase the input impedance to enhance the efficiency of the antenna system after being tuned with the matching network,and the antenna can realize flexible working mode changes in a wide frequency band.Optimizing the size,number and position of the loaded conduction bands and the configurations of the switches,the design performance of the airborne shortwave antenna was obtained.The scaling test-piece of reconfigurable antenna is also fabricated and measured with the matching network circuit compared with the traditional airborne shortwave antenna.The measured results are basically same as the simulation results,and it proves that the performance improvement of the shortwave antenna and the rationality and feasibility of the program.