DESIGN AND FABRICATION OF MICROSTRIP REFLECTARRAY USING PATCHES OF VARIABLE SIZE

Abstract

In recent years there has been an increasing demand for reduced mass, small volume and, at the same time, high gain antenna systems in radar, telecommunications and space-borne applications. Reflectarray has emerged as a suitable candidate to meet these requirements of modern antenna systems. A reflectarray consists of an aperture of elementary antennas placed on a grid and illuminated by a feed. The reflectarray feed illuminates the elementary antennas which in turn are designed to scatter or reradiate the incident field with a planar phase front in a designated direction. The elementary antennas can be of various types. However, due to manufacturing simplicity and requirements of light weight and low profile, microstrip antennas are the dominant type of elementary antennas in reflectarrays. This combination of microstrip elementary antennas and reflectarray is named a “Microstrip Reflectarray”. In this work, complete design procedure of a microstrip reflectarray using variablesized patches as elementary antennas is studied. A progressive phase distribution on aperture of reflectarray has been achieved by adjusting the dimensions of the microstrip patches. Required phase on each unit cell of reflectarray is obtained through mathematical analysis while length of microstrip patches corresponding to these phases is obtained by employing infinite array approach and waveguide simulator approach in commercially available full wave EM simulation softwares. A 29x29 center-fed broadside reflectarray at 16 GHz, using FR-4 substrate, has been designed and fabricated to validate the design procedure. Measured gain from reflectarray was 22.2 dB as opposed to a simulated gain of 24.7 dB. Close agreement between measured and simulated radiation patterns confirmed the described design procedure of reflectarray. Based on this confirmed design process, reflectarray using Rogers RT5870 substrate has been designed and simulated which shows an improvement of about 4 dB in gain as opposed to reflectarray with FR-4 substrate. Using the same design process, reflectarray with different aperture shapes has been designed and simulated. Reflectarray with circular aperture gives an improvement of about 4 dB while reflectarray with hexagonal aperture gives an improvement of about 2 dB in side lobe level as compared to reflectarray with square aperture. Also, based on described design process, reflectarray with different grid settings of elementary iv _______________________________________________________________ Design and Fabrication of Microstrip Reflectarray using Patches of Variable Size antennas on its aperture has been designed and simulated. Significant improvements in grating lobes have been observed in simulated radiation patterns of reflectarray with different grid settings of elementary antennas on its aperture. Greatest improvements in grating lobes have been observed for circular reflectarray with circular grid as opposed to circular reflectarray with rectangular grid.