Study On Impedance Measurement System For HF Antennas

In China, with the rapid development of the wireless communication, the antenna industry has occupied an important position in China's national economy. But the development of HF antennas is relatively backward. Impedance measurement is the primary problem for HF antennas. It is difficult to measure the impedance of HF antenna via traditional measurement systems due to the fact that they have a large volume and are usually erected in field. Aiming at this problem, a simple and portable impedance measurement system is designed and constructed for HF antennas in this thesis. Specifically, the major contributions of this thesis are summarized as follows:1. At first, this paper deeply studied the basic knowledge of the antenna impedance, and on the basis of the analysis of the antenna impedance measurement four methods: measuring line, the reflection method, long sweep method, bridge method. According to the four kinds of antenna impedance measurement method, and through analysis on Agilent N5230 A network analyzer impedance measurement principle, giving full consideration to the measurement system mainly in the short wave band, the final decision based on the set of parameter double directional coupling of antenna impedance measurement system.2. A lumped-parameter bidirectional coupler in HF band is designed, simulated and measured. Firstly, the series-parallel coupling of voltage transformer is analyzed. Secondly, the theory of directional coupler is introduced briefly and a bidirectional coupler using three magnetic rings is designed. Thirdly, the bidirectional coupler is simulated and the value of the element is optimized by using the commercial software ADS2009. Lastly, the bidirectional coupled is designed and measured. The measured results show that the coupling of the coupler is 30 d B ± 0.5d B, the directivity is greater than 20 d B, the insertion loss is less than 0.3d B and port VSWR less than 1.25. The bidirectional coupler satisfies performance requirement.3. An impedance measurement system is built for HF antennas. Firstly, the operation principle of the system is analyzed deeply and the feasibility of the system is demonstrated. Secondly, signal source and detection chip is selected properly. The principle and function of the components of the system is introduced.