Research On Satellite Digital Multi-Beam Phased Array Antenna Key Techniques

Multi-beam antenna is a key technique to increase satellite communication system's capability and antenna coverage rate. With the development of digital signal processing device and microwave monolithic integrated circuit(MMIC) technology makes it impossible to using digital multi-beam phased array technique in LEO satellite mobile communication system. Multi-beam antenna beam shaping technology, radio frequency channels' amplitude and phase errors analysis and correction, as well as nonlinearity distortion analysis of power amplifiers are key techniques in design and analysis of satellite digital multi-beam phased array antenna system. In this paper, these key techniques have been studied.In LEO satellite communication system, "iso-flux" illumination and beam shaping are key techniques of improving antenna coverage rate and communication capability. Different from the receiving beam shaping , for the transmitting beam shaping, the effects of the amplitude weighted on power amplifiers' efficiency must be considered. In this paper, a transmitting beam shaping scheme with limited amplitude weighted values is presented. The array weighted vectors' optimization are implemented by a dual coding genetic algorithm. Phase and amplitude of array weighted vectors are encoded by real coding and finite bit length binary coding, respectively, which, reduces the amplitude dynamic range and improves the power amplifiers' efficiency . In order to overcome the prematurity and obtain better global optimization or quasi-global optimization, a new dual coding genetic algorithm based on "species diversity retention" strategy and adaptive crossover and mutation probability is presented. The presented method can gain the tradeoff between lower sidelobe and higher power amplifiers' efficiency.Amplitude and phase errors among radio frequency channels have always been a research focus and have a critical effect on DBF system's performance. Usually, the sidelobe level, beam pointing and pattern gain are considered. In recent years, error vector magnitude (EVM), which has been applied to many commercial standards, is used widely to evaluate and analyze the communication system performance and characterizes the error between the actual signal and reference signal. So in this paper, evaluating the effects of amplitude and phase errors on DBF system performance by EVM parameter is presented and validated by computer simulation. The research shows the introduction of EVM can fully describe the transmission signal's impairment due to amplitude and phase errors and simplify the testing complexity of DBF system.In changeable space environment, amplitude and phase errors among radio frequency channels need to be calibrated frequently and quickly since the errors easily occurs due to thermal characteristics of each radio frequency circuit. A satellite-ground loop calibration scheme based on m/WH composite orthogonal codes is presented. The result shows the method is more robust. The effect of additional path-loss in LEO satellite communication system on calibration accuracy is then further studied.For the satellite-ground calibration scheme, the calculation of calibration coefficient is easily affected by satellite-ground links' performance, to avoid the effect, a calibration method based on onboard processing is proposed. This method is conducted by receiving the sum of the output signal of all radio frequency channels, including the temporally multiplexed orthogonal codes injected from the base-band, the calibration factors for all radio frequency channels can be simultaneously obtained by temporal correlation of the orthogonal codes and the IDFT parallel processing technology. The simulation shows the proposed method can effectively calibrate the amplitude and phase errors among radio frequency channels.The power amplifiers , which are the most importmant component of the transmitting device in satellite digital multi-beam phased array antenna system, are the nonilinear distortion's main source, the in-band and out-band distortion produced affect the DBF system's performance greatly. In this paper, firstly, for the multi-beam system, a mathematic model is found to study the 3rd intermodulation beams. Then, through the ADS software, a system-level simulation model for DBF system is found. Combining with the CDMA and OFDM, this work researches out-band and in-band distortion behavior of DBF system and discusses the effect of final stage filter on DBF system's nonlinearity distortion characteristic. The results show the final stage filter's existence makes in-band distortion increase and out-band distortion decrease. System-level simulation can effectively evaluate the system's performance , reduce the risk of system design and give the reference for satellite DBF system's engineering implement.