Delay Insensitive Signal-Injection Calibration for Large Antenna Arrays Using Passive Hierarchical Networks

Efficient beamforming of phased-array antennas requires that the phase delay of each channel is accurately known. One technique for achieving this is to distribute a calibration or local-oscillator reference signal through a delay-insensitive signal distribution network. In this paper, we propose using passive hierarchical signal distribution networks to distribute such signals, a method that scales significantly better with the size of the array than existing signal distribution methods. We analyze the impact of impedance variations within the network on the phase accuracy and propose a calibration front-end architecture. This front end also enables the return loss and coupling between antennas to be monitored for diagnostic purposes. We present an implementation of this front end that was applied to a small prototype antenna array, and show that this implementation exhibited low sensitivity to delays within the calibration network, reduced the temperature-dependent phase error of the front ends substantially, and can be used for performing antenna return-loss measurements.