Research On Planning And Shaping Of Digital Multi-beam Antenna Array

The thesis studies the digital multi-beam antenna technology for low-orbit satellites,focusing on the beam planning method based on equal flux coverage and the beamforming method based on particle swarm optimization algorithm.The path loss of low-orbit satellites at different angles is quite different.In order to make the transmit and receive power between the satellite and different positions on the ground consistent and reduce signal interference,an equal-flux coverage design is usually adopted.It requires small near-end gain and large far-end gain,which is a design principle to be considered when planning and shaping beams.The thesis first introduces the working principle of digital multi-beam antenna.And on the basis of the sum calculation method of antenna array pattern,the thesis deduces the calculation method of fast Fourier pattern suitable for planar rectangular array or triangular array.According to the design objective of multi-beam coverage of low-orbit satellites and the characteristics of satellite antennas,a regular hexagonal array composed of 91 microstrip antenna elements is designed.Next,a model of beam-forming optimization problem for low-orbit satellites is established,which is a multi-objective optimization problem,and then the particle swarm optimization algorithm is adopted to solve the problem.In addition,in order to improve the solution efficiency of particle swarm optimization,a sequential optimization strategy is introduced,which divides the Optimization process into parts.On the basis of the optimization results of the previous part,the next part increases the optimization goal and continues to optimize.In this thesis,the effectiveness of the strategy in improving the efficiency of particle swarm optimization is verified by a series of simulations.According to the characteristics of low-orbit satellite beam coverage,the thesis proposes a planning method based on equal flux coverage,which can accurately obtain the number and size of beam cells covering a designated area.Aiming at the beam coverage problem in this thesis,a three-layer beam coverage scheme is designed and beamforming is performed.Under the condition that the main lobe gain is met,the side lobe level is well controlled,and the transmit beam side lobe level is lower than-10 d B,the receive beam side lobe level is lower than-15 d B.Finally,based on the beamforming results,the carrier-to-interference(C/I)ratio of frequency reuse is optimized,the C/I values are all greater than 16 d B.