Research On High Gain Characteristics Of Luneburg Lens Antenna And Magnetic Short-wave Antenna

The antenna gain is the main indicator of an antenna system,and the higher the antenna gain,the stronger the anti-jamming ability and the farther the communication distance.Therefore,high gain antennas are widely applied in many fields such as modern radar,mobile communication and satellite communication.The aperture efficiency and radiation efficiency of the antenna are important factors affecting the antenna gain,so the aperture efficiency of the Luneburg lens antenna and the radiation efficiency of the magnetic short-wave antenna are studied and analyzed in this dissertation.1.Effects of the permittivity distribution of the lens and the radiation pattern of the feed on the gain of the Luneburg lens antenna(1)Based on the transformation optics(TO)theory and the focusing property of the generalized Luneburg lens(GLL),a design of a flat GLL antenna with the performances of high gain and low profile is proposed.Simulation results show that the present flat GLL antenna not only has a gain(18.4dB)of 0.6 dB higher than that(17.8dB)of the flat traditional Luneburg lens(TLL)antenna,but also has a profile of 15%lower than that of the flat TLL antenna.(2)Based on geometric optics(GO)and aperture antennas theory,the effect of the radiation pattern of the feed on the gain of the TLL antenna is analyzed in detail.The formula of the optimal radiation pattern of the feed is theoretically derived,required to maximize the gain of the TLL antenna.The theoretical and simulated results show that the gain of the TLL antenna first increases and then decreases as the half-power beamwidth(HPBW)of the feed increases,which is independent of the antenna types.Especially,the gain of the TLL antenna is the highest when the HPBW of the feed is about 68°.Several different feed antennas and a prototype of Luneburg lens are designed and fabricated.The measured results are in good agreement with the theoretical and simulated results.2.Radiation efficiency of the magnetic short-wave antennaTo improve the traveling wave transmission,the length of the traditional helix antenna should be much longer than its working wavelength,which is to cancel the generated field each other and lower the radiation efficiency.Here,an alternately rewinding method to construct the helix coils is proposed to overcome the problem.An antenna composed of six sets of ferrite helix coils is designed based on the alternately rewinding method.The adjacent two sets of ferrite helix coils are implemented by opposite winding methods,thus the fields generated by each set of the ferrite spiral coil in space are superimposed on each other.Simulation results show that the radiation efficiency of the electrically small short-wave antenna designed using the alternately rewinding method is much higher than that of electrically short-wave antenna designed using the original winding method.