Adaptive gain optimization of a C-Band reflectarray with phase tunable elements

Microstrip reflectarray antennas are currently considered for satellite missions requiring low cost, small stowage volume during launch and lightweight solutions. An essential characteristic of this kind of antenna is the possibility of having a steerable main beam due to the reflectarray´s phase-tunable elements. The tunable units could be made of varactors diodes, as described in (Riel and Laurin, 2005). Following this work, a planar array prototype of 5x6 elements was used to demonstrate beam steering capability, but unexpected differences of 2 dB or more were noted between the measured and expected gains. It was conjectured that this loss could be attributed to non-optimal phase profiles imposed on the elements, possibly resulting from variability in the diodes, non-constant angle of incidence, fabrication errors, etc. The object of this paper is to implement an adaptive gain optimization and determine to what level the unexpected losses can be compensated by tuning all the scattering cells.