Modeling of compact antennas for wireless communication in complex environment.

摘要

Demand for low-profile and compact antennas has greatly increased due to miniaturization of electronic devices. High performance for these antennas is also desired. The conflicting nature of the requirements of high performance and compact size makes the design of these antennas challenging. The primary focus of this dissertation is to investigate and enhance the performance of various compact and low-profile antennas for wireless communications.; Two dual band antennas for handheld telephones have been designed for the operation in AMPS and PCS bands and investigated in presence of the user's head. Antenna performance is evaluated in terms of VSWR, far-field radiation patterns, and the specific absorption rate (SAR) of energy in the user's head. A finite difference time domain (FDTD) code has been used for the modeling of antennas and user's head.; Two wide band circularly polarized patch antennas have also been analyzed using an FDTD code. A Moment Method based code (Ensemble) has been used to verify the performance of the antennas. Excitation of surface waves within the substrate of patch antennas is one of the main reasons for their low efficiency. Recently developed 2D planar photonic band gap (PBG) structures can be used to prevent the propagation of these unwanted surface waves within a particular frequency band. An analytical model has been developed for two existing PBG structures that predicts the band gaps for these structures. A new PBG structure with lower operating frequency and multiple stop bands has also been developed and modeled using the proposed analytical model. The analytical results have been compared with FDTD computed results and a good agreement has been found. Finally, a wide band circularly polarized patch has been further analyzed and integrated with a PBG structure. A significant improvement in the antenna performance is obtained with the use of PBG structure. The numerical results obtained are in excellent agreement with the measured data.