Design Of Circularly Polarized Waveguide Slot Arrays

With the increasing requirements for Radar Anti-jamming Performance, thedevelopment of the pulsed Doppler radar and the applications of the visualmeteorological radar, antennas are required a narrow beam or shaped beam, and a lowor very low sidelobe performance. Waveguide slot antenna has been widely applied inthe missile-borne and airborne radar equipment, etc, for easy to control the orofacialdistribution, high radiation efficiency, compact structure, reliable performance, easy toimplement a low sidelobe narrow beam or Ultra-Low Sidelobe, and many otheradvantages. In addition, with the rapid development of modern communicationtechnology, the work environment has been becoming more and more complex, whichproposes higher requirements for circularly polarized antenna performance and itsanti-jamming capability. There are many theories and approaches for waveguide slotarray antenna design, but most of them are developed for linearly polarized arrays. Sohow to design a waveguide slot array antenna for circularly polarized radiation is thefocus of this paper.In the first part of this paper, the basic theories of waveguide slot array antenna areintroduced, including how to analyze the waveguide slot antenna equivalent circuit, howto obtain the equivalent conductance formulas and how to design the waveguide slotarray antenna. Then the polarization characteristics of the antenna are presented.Under guidance of the above theories, five waveguide slot elements are designedwhich have both circularly polarized radiation and good axial ratio characteristics. Andfor the feasibility for these elements to work as an antenna array, two of the waveguideslot modular forms are chosen to realize a broadside circularly polarized waveguide slotarray with98elements. According to the simulation results, the axial ratio bandwidthfor the antenna array with dipole-circular polarizer is narrow, less than50MHz. Whilethe axial ratio for the antenna array with waveguide-circular polarizer is less than2.5dBfrom9GHz to9.5GHz.,the main beam width is less than1.6°and the sidelobe is lessthan-25dB which meet the requirements. Finally, a waveguide slot planar array isdesigned and analyzed. the simulations results indicates the maximum value of the axialratio is2.17dB during the whole operate frequency, better than that of single waveguide.