Adaptive antennas: the calibration problem

Adaptive antennas are recognized as a means of increasing the performance of communications systems. However, practical realization of such systems relies on suitable calibration of distortion effects caused by the circuitry and antenna structures. This work presents a detailed analysis of the classes of distortion that degrade the performance of adaptive antennas. This uses the results of an adaptive antenna testbed employing an eight-element circular array to illustrate the impact of temperature on performance. Design techniques that aid calibration are then described. In particular, digital downconversion, array design, harmonic sampling, sample clock dither, and clock management are discussed as a means of designing an adaptive array with the calibration problem in mind.