Adjoint Optimization of Reflectarray Antennas in the Presence of Failures

Reflectarrays (RA) are frequently being deployed in place of traditional phased arrays due to their advantages of spatial feeding, high gain, and low power consumption. Compared with phased arrays, RA performance is more dependent on the unit cells comprising the array. Thus, it is important to understand the impact that both environmental and systematic failures have on individual unit cells and how these effects translate to reduced array performance. A primary technique to mitigate these failures and extend the lifetime of the array is to retune the remaining working elements to recover the lost performance. A variety of recovery techniques have been investigated and successfully applied to phased arrays using array factor analysis. However, more complex RAs composed of hundreds of elements may not accurately be represented with an array factor. To overcome these complications, we propose the use of adjoint optimization paired with full-wave simulations to efficiently retune RAs affected by random phase failures. We demonstrate an exemplary case that applies this approach to a 625-element offset fed reflector to recover 0.9 dB of 2.9 dB lost from a 24% element failure.