Design And Research Of Adaptive Tuning Function Of Spaceborne Low-frequency Stepper Radar Antenna

As one of the key technologies of wireless communication equipment,antenna tuning(impedance matching)is not only related to the transmission efficiency of communication signals,but also an effective way to reduce the reflected current of the transmission line and ensure the normal operation of the system.The spaceborne low-frequency frequency stepping radar is a low-power,ultra-wideband space plasma detection system,using a 500-meter dipole antenna,covering the transmit frequency range of 30 k Hz to 3 MHz in 5% steps.At most frequency points,the fixed-size dipole antenna is in a state of impedance mismatch,which seriously affects the quality of signal transmission and the stability of the system.On the other hand,the antenna is in a constantly changing space plasma environment,and the plasma medium will couple with the antenna,change the input impedance of the antenna,and further aggravate the impedance mismatch of the antenna.Therefore,the traditional broadband impedance matching network with fixed parameters is not suitable for the tuning of spaceborne antennas.Aiming at the 500-meter dipole antenna of spaceborne low frequency frequency stepping radar,combined with the existing antenna tuning theory and technology,the design concept of antenna adaptive tuning function is proposed to solve the impedance mismatch problem of the antenna in the space plasma environment.In this method,the Langmuir probe is used to obtain the plasma-related parameters in the space environment,and the onoff state of the matching network is adjusted by querying the parameter table of the impedance matching network optimized based on the particle swarm algorithm to complete the adaptive tuning of the spaceborne antenna.The principle of antenna adaptive tuning is introduced,and the working principle of each component module of the adaptive tuning system is analyzed.Through theoretical derivation,the parameters of the impedance matching network with different structures such as L-type and Ⅱ-type and the expression of the corresponding standing wave ratio parameters are given..The principles of two classic adaptive tuning optimization algorithms,genetic algorithm and particle swarm optimization algorithm,are briefly summarized.For the simulation data of some frequency points with large imaginary part of input impedance and high matching difficulty of 500-meter dipole antenna of spaceborne radar,based on Genetic algorithm and particle swarm algorithm optimize the parameters of impedance matching network.The characteristics and differences of the two algorithms in the optimization of adaptive tuning impedance matching parameters are compared and analyzed through simulation.Aiming at the premature convergence problem of the standard particle swarm optimization algorithm,the optimization accuracy of the particle swarm optimization algorithm is further improved by adjusting the relevant parameters to make them adaptively change with the algorithm iteration process.The design of the adaptive tuning related module of the spaceborne radar antenna is carried out.Based on the spatial plasma electron density distribution detection data,the impedance characteristics of the 500-meter dipole antenna in the plasma environment were simulated through theoretical derivation and electromagnetic simulation.Combined with the simulation data,the Ⅱ-type tunable impedance matching network was optimized and designed by particle swarm algorithm.,and summarizes the parameter table of the adjustable components of the matching network when the VSWR requirements are met under different operating frequencies and different plasma frequencies,and further optimizes the adaptive tuning speed by looking up the table.Aiming at the inconsistency between the actual value and the calibrated value of the matching network inductance and capacitance elements in the practical application,the influence of the error between the actual value and the calibrated value of the components on the antenna matching VSWR is quantitatively analyzed.On the basis of the structure of the 500-meter dipole antenna of spaceborne radar,and by appropriately reducing the size of the antenna,a 2-meter and 12-meter monopole antenna with an octagonal wire grounding structure was designed and fabricated,and used as the transmitting antenna.,Combined with the USRP software radio platform,some frequency point signal transmission and reception test experiments were carried out to verify the feasibility of the monopole antenna design of this structure,and to provide a certain reference for the subsequent engineering design of spaceborne radar antennas.