Design and Analysis of Low-cost Reconfigurable Antennas

低成本可重構天線的設計與分析

Student thesis: Doctoral Thesis

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Award date24 Aug 2018

Abstract

This thesis presents the designs of low-cost reconfigurable antennas for wireless communications. In particular, several polarization reconfigurable designs based on the complementary antenna and the Fabry-Perot resonator antenna using cost-effective reconfigurable mechanisms such as the PIN-diode-control method and the mechanical-tuning method, respectively, have been proposed. In the described works, efforts have been devoted to realizing desired antenna performances and optimal configurations including more states of polarization control, wider common bandwidth, higher antenna efficiency, simpler biasing circuit and less feeding ports.
Firstly, a circular polarization reconfigurable design based on the circularly polarized (CP) complementary antenna concept has been investigated as a reference for evaluating the bandwidth and efficiency. This omnidirectional CP antenna features a compact form and simple structure by obtaining the magnetic dipole response from a planar patch and the electric dipole response using meandering lines. However, its bandwidth and antenna efficiency may not be that competitive. We then proceed to develop a high-efficiency reconfigurable magneto-electric (ME) dipole antenna that exhibits a wide common impedance and axial ratio (AR) bandwidth for three possible polarization states including one linear polarization and two orthogonal circular polarizations. The wide bandwidth and high antenna efficiency are ensured by combining a new excitation technique and low-loss reconfigurable perturbations. The measurement of the antenna prototype shows an common bandwidth of 7.9% (22.6% in simulation, degradation mainly caused by misalignment during antenna assembly), an antenna efficiency approaches 80~90% and a back radiation level lower than -20dB for all states. 
Secondly, to explore the possibility of achieving both linear and circular polarization diversities with only one feeding port, reconfigurable ME dipoles with switchable operation frequency band for two possible linear polarizations and up to four states of polarization control (two orthogonal linear polarizations and two orthogonal circular polarizations) are designed by incorporating a cross dipole structure as the feeding structure. The idea of adopting a cross-dipole to excite the ME dipole allows us to separate the control for linear and circular polarizations and further simplifies the whole antenna structure. Furthermore, in this quad-polarization diversity reconfigurable design, the operation frequency of the two linear polarizations can be switched between two adjacent bands utilizing the same reconfigurable perturbations initially aimed to launch circular polarizations. Measurements conducted depict an overlapped return loss bandwidth (S11< -10 dB) of 21.5% for the two linear polarization states, and 17.8% for the two circular polarization states, and a measured overlapped 3-dB AR bandwidth about 3.6% is observed.
Finally, we extend our study on polarization reconfigurability to a type of medium to high gain antenna, i.e., the Fabry-Perot resonator antenna (FPRA). We have successfully developed an unconventional gain bandwidth broaden technique for the FPRA based on the open resonator theory, as well as demonstrated a new way to generate CP beam using a hybrid-metamaterial-loaded cavity. A mechanically polarization reconfigurable FPRA that can reconfigure its polarization between two orthogonal circular polarization states and one linear polarization state is proposed standing on the two aforementioned methods. A 3D-printed all-dielectric metamaterial structure is designed either as a cavity-integrated polarizer to produce CP beam or to enhance the gain bandwidth for the linearly polarized (LP) state when it is mechanically rotated by different angle with respect to the feed antenna. This new configuration of achieving CP radiation and altering the polarization of the FPRA results in a measured common bandwidth of 6.7% for 10-dB return loss and 3-dB AR in the CP states and demonstrates a wide 2-dB gain bandwidth of 11.5% in one of the LP cases.