Research On Multi-frequency Square Loop Based Antennas With Circular Polarization And Broad Beamwidth

Modern communication requires antennas with more properties, such as multi-frequency, circular polarization, broad beamwidth and etc. In the dissertation. based on the analysis of square loop antenna, the design of the loop antenna with multi-frequency, broad beamwidth and circular polarization is proposed.The first chapter gives a brief introduction of the situation of the research on loop antennas with circular polarization, multi-frequency and broad beamwidth, respectively.In the second chapter, the principle, that square loop antenna with traveling wave current distribution can radiate circularly polarized electromagnetic wave, has been firstly analyzed. Then loops loaded with gap or opened stub have been designed to realize traveling wave current distribution, which can radiate circularly polarized electromagnetic wave. Compared to gap-loaded loop antenna, loop antenna with opened stub loaded is smaller and shows better circularly-polarized radiation.Based on the work above, an integrated structure with four circularly polarized square-loop antennas has been designed in the third chapter, in which the four square-loop antennas are stacked from lower to upper according to their working wavelengths. A novel fed configuration of "?" is proposed, which can provide a good matching for four loops. Simulated and measured results coincide well, which verify a validity of the present design.In the fourth chapter, the aperture-bound method (ABM) is employed. By introducing a square grounded wall around the loop antenna, the radiation beamwidth of the loop antenna can be broadened.In the fifth chapter, an antenna with four working frequencies and circular polarization and broad beamwidth has been designed, fabricated and measured. Four circularly polarized square-loop antennas, each with an opened stub loaded, are stacked from lower to upper according to their working wavelengths. The fed configuration of "?" is used to feed all four loop antennas while a metal grounded wall is introduced to enclose the present structure. Simulated and measured results are in good concordance except axial ratio, which can be attributed to the difference of dielectric constant of the loading foam.