The method of this paper is based on change in the geometrical shape of the reflectarray plane which is similar to a concave shape and with this changing, it is tried to make the incident waves orthogonal as much as possible in order to remove the phase error caused by incident wave variation. The other benefit of this work is omitting frequency change error caused by path difference between reflectarray antenna bandwidth. Two types of reflectarray antennas operating at X-band frequency with a linear polarization are considered in this design: concave and flat reflectarray antennas with the diameter of 135 mm. elements which are used in this paper are variable-size patches. The proposed reflectarray antenna (concave) approximately has 25% 3-dB bandwidth which shows an increment in bandwidth about 18% compared to flat reflectarray antenna.
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