Development Of High Precision Digital Vector Modulator

As the core components of interference canceller, vector modulator can attenuate signal to a certain amplitude and phase shift modulate signal at any angle, making the modulated signal and the interference signal are equal in amplitude and opposite in phase, to achieve offset against interfering signals. It is mainly used in interference cancellation technology to solve the problem of co-channel blocking interference. With the development trend of miniaturization of systems, when a transmitter and a receiver are at the same platform, it will may cause serious interference because of the isolation between transmit and receive antennas usually does not meet the requirements.Since in VHF / UHF bands, digital vector modulator for domestic engineering applications is basically a blank state, so this paper is intend to complete the development of high-precision digital vector modulator prototype which will meet the engineering applications’ requirements.This paper firstly introduces the theoretical model and the modulation process of vector modulator, analyzing the reason for low precision of traditional vector modulators from two aspects of core components and theoretical models, proposing a high-precision vector modulator scheme. It is considered in this paper that the control method using analog signal vector modulator is not suitable for practical application, thus a kind of control system with high-precision vector modulator based on FPGA is designed and developed to solve the problem of complexity of traditional vector modulator.Then, according to the proposed high-precision vector modulator scheme, this paper completed the development of high-precision digital vector modulator prototype including structural design, control system design, hardware circuit design and other aspects. Since the application environment of high-precision digital vector modulator itself is serious full of electromagnetic interference, we used the divided-space shielding technology in structure design. And when designing the control system, combined with the research objectives of this paper, we did a detail design in control scheme and data format, so that we could calculate the amounts of attenuation of bipolar attenuators in I-channel and Q-channel modulations according to the expected amount of amplitude modulation and phase modulation of the signal to be modulated. Further, since the attenuator is controlled by the voltage, we could conclude the specific relationship between control information and control voltage. Thus, the design of control voltage generated circuit and the control circuit had been achieved in hardware circuit designing.Because of the errors in system, all the control voltages of attenuators in each expected attenuating state must be debugged to get the accurate values. In order to solve the problem that the period of artificial debugging was too long to satisfy the engineering application requirements which was caused by huge workload and complex debug process, we built a automatic debugging platform based on automatic debugging system, and designed efficient automatic calibration algorithm, finally completed the debugging work of the high-precision digital vector modulator. The quotas of the developed high-precision digital vector modulator prototype all meet the design objectives.