Design of Reconfigurable Dielectric Resonator Antennas for Wireless Communication Systems

應用於無線通訊中的可重構介質諧振器天線設計

Student thesis: Doctoral Thesis

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Award date20 Sep 2018

Abstract

This thesis explores a series of novel approaches to realize a reconfigurable dielectric resonator antenna (DRA) with high radiation efficiency. Various functional DRAs have been achieved, such as a pattern-reconfigurable DRA, circular-polarization reconfigurable DRA, linear-polarization reconfigurable DRA and multi-polarization reconfigurable DRA. Several new methods are proposed, including using solid and liquid dielectric materials to reconfigure the resonant modes, using pure fluidic dielectric material to relocate the radiator, injecting liquid metal to disorder the electric-field distribution and integrating a p-i-n diode-based polarizer. The DRA is a reliable candidate for a wireless communication system due to its attractive features, such as its broadband frequency characteristics, high radiation efficiency and simple excitation. However, the advantages of DRAs, such as their high radiation efficiency and simple excitation were sacrificed to achieve the reconfiguration in most reported reconfigurable DRA designs. In this thesis, we propose several methods that not only contributed to the reconfiguration but also retained the advantages of the DRA.

First, a pattern-reconfigurable DRA is introduced using solid and liquid dielectric material to reconfigure the resonant modes of the DRA. The pattern-reconfigurable DRA maintained its high efficiency and simple excitation. The antenna is composed of two zones: the inner zone is a solid cylinder fabricated by K9 glass (εr = 6.85) and the outer zone is filled with a dielectric liquid — ethyl acetate (εr = 7.1). The liquid and solid material are packaged by a cylindrical container fabricated by 3-D printing technology and directly excited by a single axial probe. The broadside HE11δ mode is excited in the inner glass DRA when the liquid solution is absent while the conical TM01δ mode is excited in the hybrid cylindrical DRA when the liquid solution is pumped in. Consequently, a pattern-reconfiguration of broadside and conical radiation patterns is achieved across a wide impedance bandwidth of 35.5 % from 3.75 to 5.37 GHz.

Then, we developed a circular-polarization reconfigurable DRA using pure fluidic material to relocate the radiator. The resulting liquid DRA performed with a wide axial ratio (AR) bandwidth and high radiation efficiency. The liquid DRA is built by ethyl acetate and excited by a single axial probe. A 3-D printed container is designed with two zones to realize the CP reconfigurability. As a result, the proposed antenna obtains a CP reconfiguration with a flow-control of an ethyl acetate solution between the two zones. For demonstration, the liquid DRA is design at 2.4 GHz for RFID and WLAN application with a broad impedance bandwidth (SWR < 2) of 35.6 % fully covering the wide AR bandwidth (AR < 3 dB) of 16.3 %.

Further, we proposed a glass dielectric resonator antenna integrated with a liquid-metal polarizer for generating a polarization reconfiguration. We further improved the switch speed with high efficiency and simple excitation. The volume of the liquid flow-controlled by the pump was significantly reduced. The polarizer formed as a half-metallic loop is made by a type of liquid-metal alloy composed of gallium, indium, and tin. The electric-field distribution of the glass DRA can be altered through an injection of liquid metal into a glass DRA, resulting in different polarizations as well as polarization reconfiguration. We demonstrate the proposed technique that switch polarizations of a glass DRA between two states: a y-axis polarization (STATE 1) and a 45-degree polarization (STATE 2). The glass DRA is designed at 2.4 GHz with a wide effective bandwidth (overlapped impedance bandwidths of two states) of 18.4 % and high radiation efficiencies more than 80 %.

Finally, we initiated a p-i-n-diode-based polarizer integrated with a dielectric resonator antenna (DRA) to realize polarization reconfigurabilities. The p-i-n-diode-based polarizer finds effectively in altering the electromagnetic-field distribution of the DRA such that the polarization of the DRA can be actively changed. Unlike conventional p-i-n-diode-based reconfigurable antennas, the proposed active polarizer would not degrade radiation performance to the DRA. In this way, the antenna retains the high radiation efficiency with its simple excitation. The proposed antenna uses a simple and agile-switching mechanism to provide three switchable polarizations to the DRA including: a y-axis polarization (STATE 1), a + 45-degree polarization (STATE 2), and a – 45-degree polarization (STATE 3) across a wide effective bandwidth (overlapped bands of three states) of 15.0%. The radiation efficiencies maintain 65 -79 % in each state throughout the effective operating band.

    Research areas

  • Reconfigurable antenna, Dielectric resonator antenna, Liquid antenna