| The microstrip patch antenna and the dielectric resonator antenna (DRA) are both highlysuitable for the development of modern wireless communications, whose main advantagesinclude their small size, light weight, low cost, high efficiency, and ease of excitation. As thecarrier frequencies of modern wireless systems progress upward, the conductor loss ofmetallic antennas becomes severe and the efficiency of the antennas is reduced significantly.Conversely, the DRA has negligible metallic loss, and the only loss for a DRA is that due tothe imperfect dielectric material, which can be very small in practice, making them verysuitable for millimeter-wave systems. Although DRAs received attention originally formillimeter-wave applications, they are also widely investigated at lower microwave frequency.In addition, DRAs are volume devices that offer designers more degrees of freedom than2-D-type antennas (e.g., microstrip antennas) or1-D-type antennas (e.g., monopole antennas).This dissertation is mainly concerned with the applications of DRAs on reconfigurablepatterns, multi-frequencies, wide-band and high-gain, and cognitive radio. Based on themulti-modes characteristic, the radiation characteristics of higher-modes of the cylindricalDRAs are analyzed and the methods to design high-gian, pattern-reconfigurable,multi-frequencies DRAs are proposed by using the higher-modes; Investigations on how todesign wideband high-gain DRAs are pursued; Wideband DRAs are syudied according totheir multi-modes operation. The major contributions of this dissertation are listed as follows:1. The modes of cylindrical DRAs are analyzed in detail, and high-gain cylindricalDRAs are achieved by using their higher-modes. The method to design pattern-reconfigurableDRAs is proposed by researching excitation mechanisms and radiation patterns of differenthigher-modes. A dual-band DRA and a tri-band high-gain DRA are designed by introducing aloaded annular patch and a metallic cylinder to a higher-mode cylindrical DRA.2. In-depth studies about wideband high-gain DRAs are carried out: The high-gain modeTM12of the annular patch is used to improve the gain of the cylindrical DRA, and a widebandhigh-gain DRA is obtained by using a tri-annular patch and a metallic cylinder. An existingEBG high-gain DRA is modified to achieve further higher gain and larger bandwidth. Thebandwidth and gain enhancement of stacked-structure DRAs are analyzed and the design flowof wideband high-gain stacked cylindrical DRAs is given. A wideband high-gain DRA isobtained by using the higher-modes of a stacked DRA and a metallic cylinder, and thefeasibility and effectiveness are validated by experimental studies.3. The concept that integrating wideband and narrow-band DRA according to the wideband and narrow-band features of DRAs is proposed. The mutual coupling reductionbetween antennas when integrating multiple antennas into a limit space is studied. Theintegration concept of using a printed monopole antenna with a relatively large metallizationaera as a ground plane for an additional antenna is proposed, making the integrated antennacompact.4. A wideband rectangular DRA excited by a bevel-shaped patch is discussed, and anintegrated wideband and narrow-band rectangular DRA used for cognitive radio applicationsis presented. To reduce the mutual coupling between the two ports, two symmetrical shortcircuited strips have been introduced. In this current work, the integrated DRA is modifiedand optimized to reduce the mutual coupling between the wideband and narrow-band ports.5. Antennas for rejecting the interference in the wideband antennas are studied. A newband-notched wideband rectangular DRA is proposed. Two modified configurations areproposed to form the notched band: two symmetrical short circuited strips and a slot etched inthe feeding patch. Design principles of the proposed methods are described in detail.Compared with other band-notched wideband antennas, the proposed antenna exhibits ahigher rejection level. |
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