Design of Membrane Based Unit Cell of Large Reflectarray Antenna for SAR System

In the modern Synthetic Aperture Radar (SAR) applications, reflect array antenna (RFA) is the primary choice because of its simple planar structure, low profile, ability to stow following easy deployment. However, the structure has a narrow bandwidth, which is due to the unit-element bandwidth and spatial path delays. In this paper, the designed unit-element is a crossed loop having a square shape and a membrane-based unit-cell element. The electrical performance has been evaluated against half wavelength and sub-wavelength spacing's at the center frequency of 9.6 GHz. The antenna achieves approximately 7% bandwidth at the center frequency of 9.6 GHz respectively. To improve the reflection phase, foam-based structure is placed in between the dielectric layer and the ground plane. This helps reduce the overall weight of the RFA. The simulation results for the half wavelength element spacing show that the reflection phase variation happens up to 450.and the 90 degrees phase difference. However, the phase error performance has been improved using sub-wavelength element spacing, which is <= 20 degrees with the reflection phase variation of <= 380 degrees. Moreover, incorporating the unit-cell in 1.2m large RFA gives 39dB gain with +/- 0.5 dB variation in a gain for desired band.