Reconfigurable Dielectric Resonator Antennas for Wireless Communications


Student thesis: Doctoral Thesis

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Award date24 Aug 2021


Reconfigurable antennas are in high demand for use in modern wireless communication systems, because their radiating features, including frequency, polarization, and pattern, can be dynamically changed. Recently, dielectric resonator (DR) antennas (DRAs) have been extensively studied owing to their high efficiency, low cost, ease of excitation, and high degree of design flexibility. This thesis investigates the reconfigurable DRAs for wireless communications and is divided into three parts.

First, a novel filtering DRA that requires no filtering circuits is proposed, followed by a frequency-reconfigurable version. The basic filtering DRA deploys a rectangular DR and three slots fabricated in the ground. It is excited in the TEy1δ1 DRA mode and two slot modes. By using these modes, the antenna produces two tunable radiation nulls, providing filtering effects. Varactors are included in the basic design to extend it to a frequency-reconfigurable filtering DRA, and the antenna stopband is extended to the third harmonic. The antenna frequency is tuned by varying the voltages across the varactors, and the antenna has a continuous frequency-tuning range of 27.7% (2.15–2.84 GHz), with almost the same harmonic suppression level. Moreover, the antenna has a gain of ~5.0 dBi and a rejection level of over 16.1 dB across the stopband of up to 7.0 GHz.

Second, a compact horizontally polarized omnidirectional DRA excited in the TE011+δ mode is presented, followed by a polarization-reconfigurable design. The basic horizontally polarized DRA deploys a planar feed, consisting of a cross-shaped feed line, four coupled strips, and four curved arms with end-shorted stubs. The TE011+δ mode of the DRA is excited by the curved arms. The antenna’s intrinsic narrow bandwidth is broadened by the coupled strips, and the cross-polar field is suppressed by the end-shorted stubs. The antenna has a −10 dB impedance bandwidth of 18.1% with cross-polar levels lower than 15 dB. This basic DRA was used to design the first polarization-reconfigurable omnidirectional DRA. By controlling the diode states, one can switch the DRA between the TE011+δ and TM01δ modes, obtaining horizontal and vertical polarizations, respectively. The reconfigurable antenna has −10 dB impedance bandwidths of 16.8% (2.18–2.58 GHz) and 16.0% (2.25–2.64 GHz) in the TE011+δ and TM01δ modes, respectively. In both states, it has stable omnidirectional radiation patterns.

Third, a pattern- and polarization-reconfigurable DRA is presented. The antenna consists of a switchable feeding network and a cylindrical DR. In the feeding network, four slots are etched in the ground. Through the tuning of the phase distributions in the slots, three DR modes, including one TM01δ and two degenerated HEM113 modes, can be excited. The TM01δ mode has an omnidirectional radiation pattern, whereas the two HEM113 modes have boresight patterns with orthogonal polarizations (x- and y-polarizations). These modes are designed to operate at the same frequency, enabling both pattern and polarization reconfigurability. To verify the ideas, a reconfigurable DRA operating in the 2.4 GHz ISM band was designed.

Overall, the three studied types of reconfigurable DRAs in this thesis can meet various requirements in different application scenarios.