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Design of an all-metal reflectarray antenna for Ku-band DTV applications

Summary form only given. This paper is motived by the increasing popularity of satellite DTV applications at high frequency bands (such as at Ku- and Ka- bands), where the antennas with high directive radiations are desired to provide sufficient gains. In contrast to the popular antenna candidates of reflector antennas and phased array antennas, which suffer from either a bulky size or high energy loss in the beam forming networks (BFN), the reflectarray antennas have a flat, low profile while reducing the BFN complexity by using a space feed to illuminate the reflectarray structure. However, the current approach of implementing the reflectarray elements usually employs the PCB technology and prints the reflecting elements on the surfaces of dielectric substrates for the easy implementation with low cost. At high frequency, especially in the Ku- and Ka-bands, the dielectric loss still cause a degradation of radiation efficiency, where a 3dB gain loss has been observed in our experience. In this paper, we will present the development of a reflectarray antenna by using a metal structure, where the reflecting elements are realized by cutting slits from a rectangular metal cube in a rectangular grid. Since all structures are metal, the efficiency can be assured. In this design, reflecting elements are periodically spaced by 0.68 wavelengths at 12.45GHz. Slits with a width of 0.17 wavelengths are cut in this rectangular grid so that the reflecting elements become rectangular posts. The phases of reflecting elements are controlled by varying the depths of slits, which are simulated by considering a plane wave incident over an infinite array with a same slit depth. The phase change with respect to the variation of slits' depths is recorded. Interpolation is employed to find the required depth for the desired phase at a selected element when the array is illuminated by the radiation of feed. In this case, a horn antenna operating at Ku-band is used as the feed to illuminate the reflectarray. In the demonstrating design, a gain of more than 30 dBi at Ku-band (12.25~12.7GHz) is pursued. The feed is located below the bottom of reflectarray to avoid the blockage to the scattering from the reflectarray. This configuration will resemble the scenario of an offset reflector antenna with a flat surface. In the current study, both numerical simulation and experimental measurement over a prototype are performed. In particular, the measured data shows a gain of 31.86dBi with a 3.02 degree of -3dB beamwidth at 12.45GHz for a left-hand circularly polarized feed. The radiation efficiency is 84.88%, which is at the same efficiency level of conventional reflector antennas.