Research And Design Of Ultrashort Wave Antenna Impedance Detection System

With the increasing demand for wireless communication systems in the market,wireless communication technology ushers in an unprecedented peak of growth and continues to mature.As an important branch of wireless communication technology,the antenna tuning system matches the antenna unit to 50 ohms,which effectively increases the transmitting efficiency of the power amplifier and avoids converting a large amount of power into useless heat.Antenna impedance detector,as an important component of antenna tuning system,provides accurate impedance data for antenna tuning.It is the main content of this paper.In this paper,the antenna impedance detector can measure the antenna impedance characteristics of 30MHz-60MHz bandwidth,and record the impedance of each frequency point to form the impedance meter which will output to the main control board as the basis for impedance matching.Through in-depth investigation of several impedance detection principles,a vector network analysis method which can obtain high accuracy in high frequency and low standing wave ratio is selected.This method can also provide standing wave monitoring circuit under the condition of measuring impedance.According to this method,the paper push the structure of the impedance detection system and design each module in detail.In the system,hardware such as phase locked loop signal source,directional coupler,power divider and mixer are realized,and software such as impedance measurement algorithm and calibration algorithm is prepared.The PLL frequency source can output the frequency source of 30MHz-60MHz with 1MHz as gradient scanning frequency;The directional coupler achieves the insertion loss within 0.5dB,and the coupling degree is 27dB,the isolation degree is about 34dB;The two sub type power divider's input and output port of the insertion loss is 3dB,the isolation of its two output ports is more than 15dB;The frequency of the signal is shifted to intermediate frequency by method of superheterodyne,and the modulation invariance is maintained.The impedance is calculated by spectral analysis of FFT,and the accurate antenna impedance is obtained by calibrating three groups of loads,namely open load,short load and 50 ohm load.After completing the debugging of each module of the system,these different modules are integrated to debug the performance of the overall system,finally reaching the required precision.The system upgrade twice to solve the problems exposed during the debugging process,and it gives ideas and means to further enhance the system performance at the end of the article.