Research On Conical Beam Antenna

Conical beam antennas have received considerable attention in recent years in satellite-based communications serving road vehicles, wireless local network applications and guidance and tracking system due to their beam-slant, wide beam coverage and polarization radial-symmetry characteristics. This dissertation focuses on the analysis and design of the conical beam antennas with large beam-pointing angel, low side lobe level, low profile, circular polarization, single/dual band single/dual beam-pointing angle performances. Details are as follows.(1) Conical beam with large beam-pointing angle and low side lobe level performance is realized by using multisection circular waveguide. Two circular waveguide steps are introduced to control the aperture distribution of the antenna for the purpose of realizing the required beam pattern and impedance matching. The mode matching method is employed to predict the return loss and radiation pattern of the proposed multisection circular waveguide aperture antenna. The designed antenna exhibits good return loss, side lobe level, flare angle, and gain performance in the-lOdB impedance bandwidth of550MHz at the central frequency of35GHz.(2) A wideband circular aperture antenna with conical beam is analyzed. Printed ring slots are employed to improve the bandwidth of the aperture antenna up to12.2%at the centre frequency35GHz. This structure of low profile is very suitable for many applications and is also easy to fabricate at millimeter-wave frequencies. The mode matching method is employed to predict the return loss and radiation pattern of the proposed circular aperture antenna. In the bandwidth of32.8GHz to37.1GHz where the return loss is better than-lOdB, the peak gains at the elevation angles are from8dB to9.3dB, the elevation angles are from24degrees to31degrees, respectively.(3) Beam-switching technique is used to obtain the conical beam pattern with wide elevation angle coverage. The elevation angle of conical beam pattern radiated by circular patch antenna can be varied within a wide angular range by exciting the patch at different higher order modes. Therefore, equivalent wide coverage elevation angle can be achieved using two circular patch exited at different higher order modes switched by a high-speed SPDT switch. In order to obtain wide impedance bandwidth, two stacked circular microstrip antennas have been employed. (4) Axis-symmetric TM01and TE01modes in a circular aperture are employed as the orthogonal modes to produce the circularly polarized conical beam pattern. A printed four sequentially-rotated hook-shaped arms are employed to excite the TE01mode in a circular waveguide, while a coaxial waveguide has been used to excite the TM01mode in the same circular waveguide. Experimental results demonstrate that it can achieve a flare angle of29degrees,7.6dB gain for left-hand circularly polarized wave,600MHz impedance and axial ratio bandwidths.(5) Three novel nested horn antennas with conical beams are presented. They are used for X band dual beam-pointing angle, X/Ka band single beam-pointing angle and X/Ka band dual beam-pointing angle. Coaxial waveguide horn and circular waveguide horn are employed to generate the conical beam patterns. The inner conductor of the coaxial waveguide has been replaced by the circular waveguide horn. A TE01mode rectangular waveguide to TEM mode coaxial waveguide transition has been used to excite the coaxial waveguide horn. A radial-line waveguide4-way power divider with four SMA connectors has been employed to feed the outer nested horn maintaining the circularly symmetric excitation. The inner nested horn is fed by a simple SMA connector. This structure can make full use of the antenna aperture to obtain higher aperture efficiency and is also easy to fabricate at X/Ka band.