| With the large-scale deployment,development and application of 5G millimeter wave band,phased array transceiver systems such as millimeter wave MIMO have gradually become the main trend because of their obvious advantages in beamforming and less power consumption.However,with the increasing number of channels of phased array transceiver system and the mass requirements for real-time and portability of phased array channel calibration,the calibration and measurement using instruments such as vector network analyzer in an anechoic chamber,usually not meet the requirements.Under this background,a broadband fast amplitude and phase calibration system with small size,fast scanning speed and high measurement accuracy is studied in this paper.Combined with the analog part architecture of vector network analyzer and the digital signal processing method in spectrum analyzer,the amplitude phase calibration system consist of the RF signal sources.LO signal generation unit,test ports,receiving channels and digital signal processing part.Firstly,the architecture and components of vector network analyzer and spectrum analyzer are compared and analyzed.The theory,performance,measurement accuracy,error source and calibration method of the instruments are analyzed and described in detail,which provides theoretical guidance for the system circuit design.Secondly,the architecture of vector network analyzer is simplified and improved.According to the requirements and performance of the system,the overall hardware circuit is designed,and the reliability and feasibility of the scheme are simulated and demonstrated.Under ideal conditions,the input 1dB compression point of the whole system can reach 20 dBm,and the output signal power is 0dBm,with no more than 3dB ripple and 13 dB adjustment range in the working frequency band.Besides,a novel broadband tightly coupled directional coupler is innovatively designed for the frequency band of 8-22 GHz.The upper-lower coupled stripline has the characteristics of small size,high coupling coefficient and large bandwidth.At the same time,the transition structure between stripline and microstrip line is designed to facilitate connection with printed circuit board.The measured return loss of the coupler is less than-9dB,the coupling amount is not less than 15 dB,and the performance is good.At the same time,in order to suppress the harmonic of the RF signal,the frequency band is divided into 15GHz-18 GHz and 18GHz-22 GHz.The third-order interdigital filter is designed for the two frequency bands respectively.The measured return loss of the filter is less than-15 dB,the insertion loss is less than 3dB,and the suppression of the stopband is greater than 25 dB.In addition,aiming at the homology of LO signals,a 8GHz-22 GHz Wilkinson power divider is designed.The measured return loss is less than-13 dB and the insertion loss is about 5dB,which meets the experimental requirements.Finally,the designed broadband fast amplitude and phase calibration system is realized.The overall size of the system is 262 mm * 107 mm * 9mm,which has the advantages of low power consumption and small size.The whole system is tested.The test results show that the input 1dB compression point of the receiver is 21 dBm,the spurious suppression of the IF signal reaches 70 dBc,the SNR after digital signal processing can reach 108.2dB when the ADC’s input is close to full range,the phase calculation uncertainty of the single tone signal is about ± 1 °,the amplitude calculation error does not exceed 1%,and the whole system has good performance. |
