In orbit active array calibration for NASA's LightSAR

The proposed NASA LightSAR mission will use a synthetic aperture radar (SAR) to obtain high resolution images of the Earth. This paper proposes a technique for calibrating the NASA LightSAR active phased array antenna while in orbit. An encoding and decoding technique is used to perform simultaneous measurements of all the array elements thus obtaining an estimate of the relative phases and amplitudes in less than one second. A remote ground calibration station is used to receive the encoded and Doppler shifted signal from which the element phase and amplitudes are recovered. Post processing techniques are used to determine electrical and mechanical distortion errors from the phase measurements. Remote calibration shows potential as a method that may allow mechanical designers to relax mechanical deployment and tolerance specifications for the phased array antenna. The capacity to relax mechanical requirements may result in a simpler mechanical design which reduces cost and mass of the antenna system.