Research And Design Of Spherical Helical Antennas

In military communications satellite system, circular polarized antennas are oftenused, especially small size, lightweight and wide-beam ones, because the polarizationcharacteristics of the electric field will change in the ionosphere. At present, we oftenuse the cylindrical helical antenna and the microstrip antenna in the communicationsystem,but these antennas all have a lot of shortcomings. When the cylindrical helicalantenna radiate in the axial mode,its beamwidth and impedance bandwidth are bothnarrow,and the number of turns are large,which will lead to an increase in antenna’svolume. The microstrip antenna is a kind of resonant antennas whose bandwidth arevery limited, so only in a narrow frequency band the microstrip antenna can realizecircular polarization. The radiation properties of the spherical helix are markedlydifferent from those of the conventional cylindrical helix.Of particular interest is that,over a certain bandwidth, the proposed helix is capable of providing circularpolarization over a broad beamwidth. This property and its compact size make thespherical helix attractive to mobile radio communication systems and global positioningsystem.We have made a lot of simulation and analysis of the spherical helical antenna byusing the commercial software Ansoft HFSS and FEKO. We also point out that for sucha helix there exists in general all the three modes of radiation as in the case of thecylindrical helix.Moreover, radiation properties of the spherical helical antennas havebeen discussed in detail in this paper.Finally,a two-arm hemispherical helical antenna operating at1~6GHz band ispresented.The reflection coefficient of this antenna is less than-10dB in operatingfrequency range and the antenna radiate circular polarized wave in the axial direction.