Research On A New Omnidirectional Conformal Ultra-short Wave Antenna

Ultrashort wave conformal antenna plays an important role in wireless communication.The flexibility,concealment and anti-jamming of UAV(Unmanned Aerial Vehicle)put forward higher requirements for the bandwidth,size and shape of airborne ultrashort wave antenna.Conformal antennas with low profile,horizontal polarization and omni-directional radiation have become research hotspot of airborne antenna.The traditional VHF(Very High Frequency)conformal antenna is of mainly vertical polarization,which suffer from high profile,large size and narrow bandwidth.In this paper,for the low profile miniaturized omni-directional horizontal polarized conformal antenna,the research is carried out from two aspects of loop antenna and dipole antenna array.The bandwidth is expanded by using the principle of double resonance combination and the ultrashort wave conformal antenna is designed.The loop antenna theory and omni-directional radiation theory are discussed,and the current condition of omni-directional radiation of arbitrary size loop antenna is explored.It is concluded that the homogeneous distribution of current on the loop antenna is the sufficient condition for realizing omnidirectional radiation.Based on the above conclusions,far-field radiation characteristics of conformal loop antenna and dipole antenna array are compared.Based on the omni-directional radiation condition of the loop antenna,circular,rectangular and conformal loop antennas are designed to achieve omnidirectional radiation.On this basis,the bandwidth of the planar conformal loop antenna is extended by the method of frequency band superposition and Q value reduction.The mutual inductance effect is equivalent to the coupling effect of the parasitic structure,and the equivalent circuit diagram of the double-layer loop antenna is given,which provides the basis for the analysis of the parasitic structure.Based on the circuit principle,a new bandwidth expansion method of multi resonant point combining is proposed.Six basic combinations of double resonant combining circuit are analyzed.Based on the series connection of parallel resonant circuit and series resonant circuit and the series connection of two parallel resonant circuits,the bandwidth of practical ultrashort wave omnidirectional conformal antenna is extended.Two methods are used to realize dual resonance point merging and bandwidth expansion which are the broadband matching network of the lumped elements and the distributed structure antenna.The test bandwidth of antennas with matching network structure is 42.69MHz-44.33MHz and the simulation result of distributed antennas is 44.14MHz-45.86MHz.Based on the theory of omni-directional radiation,a deformable dipole antenna array with horizontal polarization of ultra-short wave omni-directional radiation is studied and designed,and a LC broadband matching network is designed to double the bandwidth of the dipole array antenna with gain unchanged.The working frequency band of the antenna array is 39.97MHz-44.64MHz.