Fixed multi beam offset spherical reflector antenna at 28 GHZ

Abstract

Multi beam antenna system is one of the requirements at the base station for fifth-generation (5G) mobile communication. These days, the implementation of array antenna to produce multiple beams by using digital beamforming technology (DBF) is often seen at the base station pole in urban district. However, this technology comes with expensive cost and high complexity. Therefore, multi beam reflector antenna with fixed multi beam operation is chosen as the alternative cheaper configuration for 5G base station at 28 GHz. Multi beam reflector antenna is prominent in producing high gain for long distance communication remarkably in satellite communications as the satellite mount antennas to achieve the specific area illumination on the Earth. Among the types of reflector antennas like parabola, shaped and spherical reflector, the spherical reflector antenna is superior in producing the same radiation patterns for multi beam performances. Despite that, the reliable design method to analyze the spherical reflector by identifying the effective aperture area and the best feed positions for high antenna efficiency and good multi beam radiation characteristics was not made clear. In this research, analysis of the spherical reflector by ray tracing method was developed for various incoming rays’ direction. The algorithm of the focal region ray tracing equations of spherical reflector for horizontal and slant incident rays were developed and illustrated by MATLAB program to obtain the reflected rays at the focal region. From the focal region ray tracing results at slant incident rays, the effective reflector aperture area that contributed to the small focusing region were clarified. Subsequently, an offset spherical reflector antenna configuration was formed due the effective reflector area, and the feed positions for targeted multi beam in angular region 0 degree to 30 degree were calculated. The multi beam performance of offset spherical reflector was then verified in the electromagnetic simulations of FEKO simulator. Good multi beam radiation patterns and high antenna efficiency which exceeded 70% were ensured at the angular region of 10 degree to 30 degree. In conclusion, it is shown that the offset spherical reflector can achieve high gain and good multi beam characteristic in a wide radiation angle region. The proposed design of this offset spherical reflector configuration is an excellent multi beam reflector antenna and it also provides the industry with a guide in manufacturing accurate reflectors for high gain performance.