Research On Antenna Tunable Impedance Matching Network Based On Varactor

Antenna is an important part of the wireless communication system,and its impedance value varies with the environment changes.Therefore,the impedance matching network is needed to match the antenna to the signal source in real time.The distributed parameter matching network is more suitable for high frequency.This paper mainly studies the distribution parameter matching network of the antenna.The main work of the research is as follows:An improved particle swarm optimization algorithm with learning factors varying with weight coefficients is proposed.The effects of the number of particles,the number of termination iterations,the weight coefficient and the learning factor on the convergence effect of the algorithm are studied.It is known that the improved PSO can effectively avoid the algorithm falling into the local optimal solution.The improved PSO algorithm is used to optimize the parameters of the antenna double-branch impedance matching network.It can be seen that the improved PSO algorithm converges in the 30th generation,and the return loss of the antenna at 900MHz is-32.88dB after parameter optimization.Compared with the basic PSO algorithm,it converges 10 times earlier,and the value drops more.The performance of the improved PSO algorithm is better than the basic PSO algorithm,and the improved method is feasible.A single-stub matching network is studied,and a varactor is added at the open stub of the network to form a tunable single-stub matching network.The simulation results show that the impedance matching of the real part of the antenna impedance from 9.8 Q to 13.8 ? and the imaginary part in the range of-62 ? to-74 ? can be achieved by using the tunable single-branch matching network.When the voltage is 5V,the antenna resonates at 900MHz,S11 is-33.953dB;the VSWR of the original antenna fluctuates between 20.23 and 84.97.Through the physical test,when the bias voltage is 2V,the antenna resonates at 955MHz,S11 is-28.97dB;The antenna VSWR after loading the matching network fluctuates between 1.117 and 1.538,and the matching effect is good.The triple-stub matching network is studied,and varactor diodes are added at three open stubs to form a tunable triple-stub matching network.The simulation verifies that the matching network realizes impedance matching from 1.8 ? to 51.8 ? and the imaginary part from-50 ? to-100 ?.The matching range is much larger than the tunable single-stub matching network.When the bias voltages of the three varactors are 7V?2.5V and 2.5V,respectively,the simulation can obtain the antenna resonating at 900MHz,S11 is-36.463dB,and the VSWR of the original antenna fluctuates between 24.995and 26.937;The resonance at 980MHz,S11 is-28.997dB;The VSWR of the antenna fluctuates between 1.074 and 1.732 after loading the matching network.When the bias voltage changes,the measured and simulated frequency offset trends are approximately the same.