Reflectarray to Generate Four Adjacent Beams per Feed for Multispot Satellite Antennas

Abstract

This contribution describes a design concept of a reflectarray antenna to produce four adjacent beams per feed through the simultaneous use of polarization and frequency discrimination The feed position is computed to produce two adjacent beams in different frequencies accounting for the beam squint effect, which ensures a minimum phase variation between the phase distributions at the two frequencies. The other two beams in orthogonal polarization are generated by implementing in the reflectarray a different phase-shift for each polarization. This contribution presents the design, manufacturing and measurement of a 43-cm demonstrator that operates at transmit frequencies in Ka-band. The proposed concept can be suitable for multiple spot beam satellites in Ka-band, enabling a reduction in the number of antennas and feeds needed to provide the multi-spot coverage.

Multibeam Reflectarrays in Ka-Band for Efficient Antenna Farms Onboard Broadband Communication Satellites

“…The controlled application of the beam squint effect with frequency has been used to reduce the design complexity of the reflectarray antenna, as shown in [16]. The method to generate four spaced beams in four different colors per feed has been experimentally validated in [17] for a 43 cm reflectarray antenna. The prototype operates in linear polarization (LP), but the same design technique can be applied to produce the beams in CP by an appropriate selection of the reflectarray cells.…”

“…Figure 5 shows the 43 cm prototype in the anechoic chamber and the measured radiation patterns of the four spaced beams in four different colors, according to the normalized angular coordinates u = sinθ•cosφ, v = sinθ•sinφ. Two different approaches have been evaluated to produce a multispot coverage following the design technique developed in [17]: first, using a flat reflectarray as proposed in [10], and second, using a reflectarray with a parabolic surface. The two reflectarrays are expected to generate a four-color coverage for Tx in Ka-band using the feed cluster shown in Figure 3.…”

“…The two reflectarrays are expected to generate a four-color coverage for Tx in Ka-band using the feed cluster shown in Figure 3. Due to the symmetry of the antenna system, the simulations have considered the lines of feeds A, B, and C in Figure 3 (plotted with thicker lines in Figure 3), since there Two different approaches have been evaluated to produce a multispot coverage following the design technique developed in [17]: first, using a flat reflectarray as proposed in [10], and second, using a reflectarray with a parabolic surface. The two reflectarrays are expected to generate a four-color coverage for Tx in Ka-band using the feed cluster shown in Figure 3.…”

“…A flat reflectarray has been proposed to generate four spaced beams per feed according to the design technique shown in [17]. The reflectarray has a diameter of 1.8 m and it is formed by 44125 reflectarray cells arranged in a 239 × 235 lattice, the period of which has been set to 7.5 mm to avoid grating lobes.…”

“…The use of ideal reflectarray cells prevents an accurate characterization of the cross-polar radiation, which is mainly produced by the reflectarray elements and the offset antenna configuration. Previous reflectarray prototypes with offset configurations have provided XPD above 25 dB [17,18]. the radiation patterns in the plane v = 0 for the beams generated at both frequencies.…”