On Wideband Impedance Matching Network For HF Antennas

Antenna plays a significant role in a wireless communication system. The input impedance of the antenna varies with the operating frequency and surrounding environment which will result in a mismatch between the transmitter and the antenna. The state of the impedance matching determines the amount of the power transmited from the input circuit to the output circuit. The circuit will obtain maximum power transfer when it achieves impedance matching. Therefore, impedance matching is extremely important to antenna design. Using broadband matching network a HF antenna can realize broadband characteristic. However, traditional broadband matching networks which work in HF band are usually have a poor matching performance and low efficiency. Aiming at this problem, a broadband matching network is designed for HF antennas. The impedance range is divided into several parts. And narrow band matching networks are designed for each sub-frequency band. Broadband impedance matching is realized by combining those narrow band matcing networks with switches according to the desired working frequency band. Specifically, the major contributions of this thesis are summarized as follows:1.In accordance with the agreement of matching network topology, a common topology is designed. By using the genetic optimization algorithm, a broadband matching network is designed. Firstly, the input impedance of a 3-meter antenna is measured,the band of poor impedance characteristics is chosed for matching network designing.By simulation and physical experiments, shows that the low-band impedance characteristics of the antenna.is effectively improved.2.The value of the component for the matching network is determined by interpolation method. Based on the results of the optimization, we suspect that the values of the same component satisfy a functional relationship. The center frequency as the interpolation point, the component value as the valus of the function, An approximate function is constructed to calculate the matching network component values of other bands. Through the interpolation of each component, come to the matching network of an arbitrary center frequency.The correctness of the theory is verified by Advanced Design System.