Theory And Design Of Wideband Printed Monopole Antennas And Electro-magnetic Combined Dipole Antennas

In recent years, a series of printed disc- like monopole antenna have been proposed and intensively studied by focusing on its compact size and wideband radiation characteristics. However, most of these antennas have complicated structures and lack of general design principles. Thus, it is essential to deduce the common design guidelines and approaches of these antennas. In this thesis, by introducing the correlation function of the input impedance frequency responses, several printed monopole antennas are studied and compared with each other, and a common, general operation principle is concluded. Based on this idea, a loop- monopole combined antenna for wearable applications is designed and discussed. The main content of this thesis is organized as follows:1. A novel antenna performance evaluation method of planar wideband monopoles is proposed. The correlation function of the input impedance frequency responses for different disc-like monopole antennas is introduced at first. A classical, frequency- indepedent mono-conical antenna is utilized as a “template antenna” and compared with the planar monopoles. It is demonstrated printed, disc- like monopole antennas share a common operation mechanism with conical antennas. The wideband characteristics of the printed, disc- like monopoles are less dependent to their shapes. Therefore, the wideband characteristics of these antennas can be considered as the residue of the inherent frequency- independent characteristic of the ideally infinite, non-truncated conical antennas.2. On the basis of the former idea, a wideband loop- monopole combined unidirectional antenna with simple structure is discussed. An equivalent sources model is use to reveal the basic behavior of the antenna. Then, the parameters of the antenna are analyzed and optimized by using IE3 D and CST. The simulated impeda nce bandwidth is 2.76-8.13 GHz and the antenna exhibits a cardiac-shaped, stable unidirectional beam.3. Antenna performance in proximity to human body is simulated by using a numerical human arm model. The prototypes of the antenna are fabricated and meas ured by Agilent’s 8720 ET vector network analyzer and NSI 2000 far field antenna measurement system. The simulated and measured results agree well with each other. When it is worn on different persons, stable impedance from 1.8-5.6 GHz can be achieved. The interaction between the antenna and human body could be mitigated.