李柯伽，男，1999-2009， 北京大学本、硕、博。 目前就职于北京大学天文系，兼职中国科学院国家天文台。主要研究领域为脉冲星类天体的观测和理论研究，相关研究兴趣包含射频及高速数字电路，统计信号探测。In this talk, we will discuss the low-frequency array,21cma, upgrade work and the latest observation results. The team had upgraded 2,540 antennas and performs low-frequency pulsar observations. We will introduce the key components of the array, including the low-noise amplifier, analog beamformer, and calibration system. We will also share some lessons learned from the array upgrade. The pulsar observation results will also be included in this report.