Design And Implementation Of Digital Radio Compass Antenna Simulator

The radio compass antenna simulator is widely used in the off-position detection and maintenance of radio compasses,and can simulate the radio compass antenna signal.Traditional radio compass antenna simulators are mainly electromechanical or analogue circuit structures,which are disturbed by the external environment,and have problems such as high cost,large size,complex structure,and cannot be operated off-line.Therefore,new antenna simulators with low cost,small size and digital structure need to be studied.In this thesis,a new digital radio compass antenna simulator system(NDRCAS)based on ARM and FPGA is designed to solve the above problems of the traditional radio compass antenna simulator.The NDRCAS system hardware mainly includes ARM and FPGA core circuit,signal synthesis circuit,signal selection circuit,filter circuit,signal attenuation circuit,signal acquisition circuit,human-machine interaction circuit and power supply circuit.A DACbased digital control attenuator is designed to control the amplitude of the output signal at the programmed attenuation,with low cost,wide range and small size.In the design of the lowpass filter module,the elliptical filter circuit with the best noise filtering performance was designed after comparison of the cut-off performance of four filter circuits.Meanwhile,the multiple test points and signal monitoring points are designed into the circuit for quick troubleshooting and maintenance.In order to improve the accuracy and purity of the signal output,this thesis analysed the DDS in the DRCAS system and used computer simulations of various DDS errors and methods of suppressing DDS errors.A novel fusion algorithm is proposed to suppress DDS errors,increasing the spurious-free dynamic range to 127.34 d B with a significant reduction in storage memory requirements.The NDRCAS software system is based on the new hardware and implements the software control functions of azimuth generation,DDS signal synthesis based on a novel fusion algorithm,signal acquisition and output attenuation.A new human-machine interaction is designed to solve the problems of the existing antenna simulator,which requires a host computer to control it.The system is also capable of signal source switching and output frequency calibration,and can be controlled by a host computer for basic automatic testing.The human-machine interaction,stability,signal and amplitude of the NDRCAS were tested.The results show that the human-machine interaction and the control function of the slave computer are normal,the frequency error is less than 0.1% over the whole required output range,and the amplitude can reach the required minimum and maximum values.Using a standard radio compass as the input device,the NDRCAS and the existing analogue circuit radio antenna compass simulator were compared and tested.The test results show that the NDRCAS can operate independently compared to the traditional radio compass antenna simulator and the azimuth orientation error is less than ±1° in the range of 0～360°,which is better than the design specification of less than ±2°,and can satisfy the testing and calibration requirements of the radio compass maintenance work.