Analysis of Impairments, Error Correction and Evaluation of Adaptive Antenna Arrays Based on Vector Modulators Beamforming ICs

This paper describes the impairments, calibration, evaluation and integration of core ICs for antenna beamforming using vector modulators. The analysis of the main sources of degradation in vector modulators such as amplitude and phase imbalances, quantization noise, isolation, and phase variations with amplitude control are presented. The impact of limited isolation on the system phase margin and the accuracy of phase and amplitude is also discussed. A 4-TX and 4-RX channels vector modulator core IC with 8-bit phase resolution has been fabricated. A 2-step calibration method for phase and amplitude was employed. The phase calibration is initially performed directly at the phase measurements of the core IC with a second step for amplitude calibration carried out at the antenna array. By reducing the errors associated with the quantization noise and applying 2-step calibration for the phase and amplitude, very low sidelobe levels were obtained. New applications in the area of antenna beam forming which traditionally suffered from limited suppression of the interference due to the high sidelobe levels can be explored by realizing vector modulator core ICs with having low error sources and using separate phase and amplitude calibration techniques.