Synchronous Synthesis of Microwave Modulated Signal: Spectrum Purity Control & Analysis

The issues of control and analysis the noise parameters of the spectrum during synchronous synthesis of a quadrature phase shift keying (QPSK) signal directly in the microwave range at a carrier frequency of 3.2GHz with a information speed of 200 Mbit/s are investigated. The cascade structure of the modulated signal former is considered: a serially connected a frequency synthesizer of the indirect synthesis method and a synchronous QPSK signal modulator, which are built on the basis of a phase-locked loop (PLL) system optimized for speed - a globally linearized synchronization system (GLSS). The issue of choosing the optimal loop gain coefficient of the GLSS frequency synthesizer for given noise parameters of the reference oscillator and the voltage-controlled oscillator (VCO) in the frequency synthesizer is considered in order to minimize the phase noise level in the spectrum of the GLSS frequency synthesizer signal. The simulation results demonstrate the unique features of the architecture of synchronous synthesis of modulated microwave signals: control of the phase position of the VCO in the modulator and simultaneous suppression of spectral VCO noise in the loop band of the modulator to the noise level of the spectrum of the reference microwave oscillation generated by the GLSS frequency synthesizer.