Design and measurement of channel calibration for digital array with orthogonal codes

In order to realize an accurate multi-beam forming for Digital Array Radar (DAR) system, a calibration method-the Unitary Transform Encoding (UTE)-for revising the amplitude/phase imbalance among transmitting channels is proposed. This method employs set of orthogonal codes that are sequentially applied to all channels, allowing elements to be measured in-situ simultaneously by receiving a sum signal. Intermediate Frequency (IF) signal processing has turned into its key technique because it determines the precision of calibration factors. In this paper, for testing the effectiveness of UTE method on engineering application, we design a hardware circuit platform that adopts IF software radio architecture based on FPGA. The platform integrated digital-analog converters (DAC) and analogdigital converters (ADC) so that we can realize the UTE encoded-decoded processing to obtain the calibration factors. The results of measurement show that the UTE method is a fairly effective to calibrate amplitude/phase imbalance for multi-beam DAR system and the beam pattern is considerably close to ideal beam pattern after calibration.