Abstract
Two main factors limiting the reflectarray bandwidth are different phase slopes versus the frequency at every point on the aperture and the phase limitation of comprising elements at different frequencies. Considering these two factors, a novel design method is proposed to implement a dual-band, dual-polarized reflectarray antenna in X and Ku bands. An optimization algorithm is adopted to find the optimum phase for each unit cell on the reflectarray aperture. The best geometrical parameters of the phasing elements are suggested based on the phase variation of the element versus frequency and the element position with respect to the antenna feed. Many different classes of phasing elements with identical base structures are investigated to provide a lookup table for the optimization algorithm. The optimum phases are obtained so that two collimated beams are realized within the frequencies of 10.95 GHz to 11.7 GHz and 14 GHz to 14.5 GHz with vertical and horizontal polarizations, respectively. From the experimental results, the peak directivity of 27.1 dBi and 30.6 dBi, aperture efficiency of 42% and 67%, and cross-polarization level of less than –15 dB and –20 dB were obtained in the lower and upper bands, respectively.
Highlights
Reflectarray (RA) structures consist of flat platforms of phasing elements, which are arranged in a regular or irregular lattice
Apart from conventional reflector antennas, the aperture field distribution on the reflecting surface of an RA can be engineered only by tailoring the phasing elements. This leads to developing broadband, multiband, dual, and circular polarized RAs or advanced passive and active RA configurations with beam shaping, beam scanning, nonlinear, and beam switching capabilities, which are well suited for several applications [1,2,3,4,5,6,7,8,9,10]
As a factor of superiority compared to the phase array antennas, reflectarrays use the free space as a transmission medium between the feed and phasing elements and undoubtedly mitigate the feeding loss
Summary
Reflectarray (RA) structures consist of flat platforms of phasing elements, which are arranged in a regular or irregular lattice. It can be inferred that the phase compensation versus frequency is a strict function of F/D and the local position of the cell on the reflectarray aperture from the feed point of view, where F and D are the focal length and aperture size of the antenna, respectively This factor along with the frequency dispersion at extreme frequencies of the band, which is due to bandwidth limitation of the element, are the main reasons for the narrowband behavior of a reflectarray. An appropriate search algorithm is performed on the full-wave simulation results to get the best geometrical parameters for the elements according to the required phase responses This algorithm operates according to two criteria: the element positions with respect to the feed, which forces the required phase slope for that position, and the phase range of the element as the frequency is varied. The element in the design process is the modified one reported in [17] to achieves more bandwidth, in the upper band
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