An agile high-frequency radar used for ionospheric research - Erratum

The Super Dual Radar Network (SuperDARN) is an international high-frequency (HF) radar network used to study plasma convection in the upper atmosphere. An agile SuperDARN radar (AgileDARN radar) was deployed to join the network in Jiamusi, China. The AgileDARN radar is a digital phased array radar equipped with an field-programmable gate array (FPGA)-based digital processing unit (DPU). It can operate as a standard SuperDARN radar or a multiple-input-multiple-out (MIMO) radar. Each channel can be controlled and processed separately. Digital beam forming (DBF) is used to make beam steering flexible and beam switching fast. Multiple sub-beam forming for receiving can be implemented on FPGA or computer to improve position accuracy. Additionally, internal calibration and external calibration are carried out to improve the performance of beam forming. The internal calibration is a self-calibration without any external connections. Calibration signals are produced by the generators in DPU. The gain and phase of transmitters/receivers are read and compared to the based transmitter/receiver. Then the differences are recorded to compensate for the imbalances. During the external calibration, meteor trails are used as calibration sources to detect the imbalance between antennas (including cables). The imbalances are compensated in the same way as the internal calibration. By calibration, the amplitude and phase imbalances between channels are reduced significantly.