Research On High Precision Microwave Amplitude-phase Control Technology And Broadband Digital Attenuator

Microwave and millimeter wave amplitude-phase control technology is the key technology in modern phased array radars,communication systems and test instruments.The control precision,faltness of amplitude-frequency response,and insertion loss of the amplitude-phase control circuit have important influences on the performance and function of the system.With the continuous development of new electronic systems such as phased array radars and 5G communication,higher and higher requirements are put forward for the amplitude-phase control circuits with high precision,flat amplitude-frequency response and low insertion loss characteristics.In this paper,aiming at realizing high-performance amplitude-phase control components,by utilizing the broadband voltagecontrolled attenuator chips and vector modulator chips,key technology of high-precision amplitudephase control based on high-precision digital-to-analog converter(DAC)are intensively studied.It is applied to the development of 1.0-30.0GHz ultra-wideband high-precision program-controlled attenuator and UHF-band high-precision phase shifter hardware module;In order to improve the amplitude-frequency response characteristics of commercial digital attenuator chips,the broadband amplitude equalization technology is used to develop the ultra-wideband digital attenuator with flat amplitude-frequency response and low insertion loss characteristics in the frequency range of 1.0-27.0GHz.The main research progress of this paper includes the following five aspects:1.Based on Linear’s LTC2664CUH16 digital-to-analog converter chip,the design scheme of the high-precision DAC control module is worked out,in which high-precision DAC chips are combined with dual operational amplifiers connected in parallel to enhance output current.The DAC module with 1m V output voltage accuracy under a maximum load current of 20 m A is developed to provides a key control module for realizing high-precision amplitude-phase control circuits based on digital control technology.Using ADI’s precision operational amplifier ADA4077,a current amplifier with high input impedance is designed to solve the problem that the general DAC output voltage is easily pulled by the load to worse the voltage accuracy.The communication control circuit between the DAC chips and the host computer is designed by using TI’s MSP430F2132 microcontroller,and the control program is written.Based on the platform of Microsoft Visual Studio,the host computer software is developed in the C# language,and the GUI graphical interface is designed to achieve the simple control method of the high-precision DAC module.Meanwhile,in order to realize the requirement of system cascading to expand the dynamic range,a multiple output high-precision DAC module is developed on the basis of the above-mentioned DAC module and lay the foundation for multi-channel amplitude and phase precise control.2.By making use of Tri Qunit’s TGL4203 broadband voltage-controlled attenuator chip combined with the above-mentioned multiple output DAC module,a broadband high-precision program-controlled attenuator in the frequency range of 1.0-30.0GHz is developed.Simulation of the circuit of the switching T-type structure attenuation network based on the Ga As FET has been carried out by using ADS software.The relationship between the different two groups of gate voltages and the value of network attenuation is verified,which shows that the attenuation control accuracy of0.2d B can be realized by using the gate control voltage.Based on TI’s MSP430F149 microcomputer,the SPI communication circuit and the host computer control circuit are designed.Meanwhile,the look-up table circuit is designed with the flash chip W25Q64,and the gate control voltage relation data corresponding to different attenuations is stored in the look-up table to realize the rapid analysis and query of the host computer instructions.After completing the program calibration and optimizing the broadband matching circuit,the experimental results show that the broadband program-controlled attenuator based on DAC developed in this paper has an attenuation accuracy of 0.2d B and a dynamic range of 34 d B in the frequency range of 1.0-30.0GHz.It effectively improves the control precision of the general digital attenuator of 0.5d B step.3.Based on ADI’s HMC630 vector modulator chip,combined with the above-mentioned DAC module,a high-precision phase shifter in the UHF band is developed.The phase shifter with vector modulation structure is simulated and analyzed by ADS software,and the relationship between the phase shift value and the I/Q control voltage is verified,which shows that the phase shift accuracy of1° is achieved by the I/Q control voltage.After optimizing the performance of the RF circuit,the experimental results show that the UHF band high-precision phase shifter based on DAC developed in this paper achieves a phase shift accuracy of 1° and a phase shift range of 360° in the frequency range of 800-1000 MHz.Compared with the 5.625° step of the traditional 6-bit digital phase shifter,the phase control accuracy is improved significantly.4.Based on the broadband amplitude equalization technology,a digital attenuator with flat amplitude-frequency response characteristics in the frequency range of 1.0-27.0GHz is developed by using the ADRF5730 attenuator chips of ADI.The commonly used broadband digital attenuator chips generally have the problem of excessive insertion loss at the high frequency end.In order to improve the amplitude-frequency response characteristics over the whole working frequency band,the broadband amplitude equalization technology is applied to compensate the excessive insertion loss of ADRF5730 digital attenuator chip and so as to realize a broadband digital attenuator with flat amplitude-frequency response characteristics.After optimizing the parasitic resonance and broadband matching network,the experimental results show that when the attenuation is set in the range of 0-46.0d B,the amplitude-frequency response flatness of the digital attenuator developed in this paper is better than ±1.5 d B in the frequency range of 1.0-27.0GHz.Compared with the 6.7d B before equalization,the excellent amplitude-frequency response characteristics is achieved.5.In order to solve the problem that the digital attenuator has a considerable basic insertion loss as high as 14 d B,a broadband power amplifier with appropriate gain is designed to compensate for its basic insertion loss,and the two parts are integrated to achieve digital attenuator with flat amplitudefrequency response and low insertion loss.After overcoming the parasitic resonance and optimizing the performance of the circuit,the experimental results show that the typical insertion loss of the digital attenuator developed in this paper is around 0d B in the frequency range of 1.0-27.0GHz.Compared to the insertion loss of 14 d B before compensation,it has a significant improvement and achieves the low insertion loss characteristics.When the attenuation is set in the range of 0.0 to60.0d B,the amplitude-frequency response flatness of the digital attenuator is better than ±2.5d B.It has excellent amplitude-frequency response characteristics and is suitable for broadband phased array radars and microwave/millimeter-wave testing systems.