Research Of Impedance Matching Network And Tuning Algorithm Of Antenna Tuner

The input impedance of antenna is variable with frequency seriously in short-wave communication system, so an impedance matching network with fixed parameters can not accomplish the task of antenna impedance matching. The general solution is to use an impedance matching network with variable parameters such as antenna tuner. The control circuits of matching network in traditional antenna tuner are almost based on micro controller unit (MCU), and in tuning algorithms the values of netwoek elements are adjusted gradually to accomplish the impedance matching. So the tuning speed and accuracy are low. Accompanied with the appearance of the antenna technology based on vector impedance detection, the development of tuning algorithms with high speed and accuracy used in antenna tuner become a new research project.The application and development of antenna tuner are reviewed at first in this paper, then the major targets, the tuning elements and the tuning methods of antenna tuner are introduced. The basical principles of MCU and parameter detector unit are analyzed and the antenna technology based on vector impedance detection is introduced as the last development achievement of antenna tuner.After that the properties ofГ-section matching network are analyzed, and the analyze method is extended to T-section andП-section matching network. The tuning methods of every kind of matching network are elaborated. Then a 4m whip antenna is considered to design the impedance matching network of antenna tuner based on the typicalП-section matching network. The ranges of values of elements array are estimated tentatively and the matchable domains of matching network are analyzed through simulation with different accuracies, frequencies and numbers of element. In the design of tuning algorithm, the tuning algorithm based on direct calculation is used to obtain the high speed of tuning. The performances of algorithm and network are analyzed through simulation with a 4m whip antenna and the good performance is obtained. The matching accuracy, calculation inaccuracy and how to find the best solution are analyzed. Then the nearest neighbor searching algorithm is proposed to improve the performance. Based on the analysis have done, the elements deployment of network are adjusted to obtain better performance in the same algorithm.At last, the element deployments of network are adjusted further in order to match the long antenna and the problem of matching is transformed to the optimize problem of elements combination, namely to select appropriate elements to minimize the voltage standing wave ratio (VSWR). The genetic algorithm is proposed to solve the typical problem of combinatorial optimization. The basical flow of genetic algorithm is elaborated. The element arrays are coded by binary code and the minimization of reflectance is as the function of fitness. Then a 4m whip antenna is considered and good performance is obtained. As enlightened by direct calculation and nearest neighbor searching, the tuning algorithm based on genetic algorithm is simplified. The number of variable and the space of searching are reduced, so the tuning speed and accuracy are improved obviously. It is proved by simulate that the genetic algorithm can be used as an antenna tuning algorithm.