Research On Broadband Millimeter Wave Hollow Beam Antenna

As the Conical Beam Antenna (CBA) has omni-direction characteristic in azimuth, it is easy to realize a large beam coverage area. In this context, CBAs are widely applied in navigational tracking system, fuze system and vehicle satellite communication. In this paper, two kinds of wideband CBAs at Ka-band are researched to resolve the problem of relatively narrow impedance. One antenna is waveguide structure, which has wide band, high efficiency and high gain characters. Another antenna is a microstrip array strucure, which has the advantages of wide band, low profile and high gain.Firstly, the basics and design principles of the antenna are introduced. A maximum directivity formula is derived for ideal uniform aperture field distribution by the following.Secondly, a new waveguide structure of broadband conical beam antenna at Ka waveband is designed. Adding four triangular ridge structure to the circular waveguide is proposed as the first time. By this method the coaxial waveguide is successfully transition to the open circular waveguide. As consequence, the bandwidth has extended five times compared to the traditional non-ridge structure. By simulation we can know, a flare angle of 30 degree, a impedance bandwidth of 16% in terms of VSWR less than 1.5, a gain of lOdBi at operating frequency, a relative aperture efficiency of 87%, and -3dB beam width is 27 degree, and the side lobe level is less than-10dB. Measured results are in good agreement with simulation ones, which verify the correctness of the design method.Finally, a new microstrip array of broadband conical beam antenna at Ka waveband is designed. The radiation characteristics of circular patch and the bandwidth broadening method are studied. The effects of the cell structure, pitch, and H-type slot coupling for the antenna performance are discussed. By simulation we can know, a flare angle of 30 degree, a impedance bandwidth of 17% in terms of reflection less than-10dB, a gain of 9dBi at operating frequency, and -3dB beam width is 27 degree, and the side lobe level is less than-10dB.In this paper, the two kinds of conical beam antennas can realize wideband and high gain, and have great value in engineering application.