Abstract
Since the carrier frequencies of modern wireless systems have gradually progressed up to the millimeter-wave (mm-wave) band, mm-wave antenna has become an important topic. In this dissertation, new open-cavity (OC) antennas for mm-wave mobile application are investigated. The OC antennas operate at either the resonance frequency of Fabry-Perot resonator (FPR) or the resonance frequency of feeding slot. Compared with other broad-beam/fan-beam antennas such as microstrip patch antenna and dielectric resonator antenna, the proposed antennas have larger dimensions and are therefore less sensitive to fabrication tolerances. This is important especially at mm-wave frequencies wherein the wavelengths are small.A novel planar-mirror Fabry-Perot resonator antenna fed by an L-probe is proposed. It consists of two parallel metallic plates that are perpendicular to the ground plane. Its resonance frequency is controlled by changing the separation between the parallel plates, similar to Fabry-Perot etalons. However, unlike Fabry-Perot etalons, the two parallel plates of this FPR antenna are totally reflective. Consequently, the radiation pattern of the proposed FPR antenna is different from those of existing FPR antennas, and a fan beam is obtained. A probe resonance near the FPR mode is utilized to broaden the impedance bandwidth. To reduce cross polarization, a modified version with a groove introduced on each inner surface of the plates is also investigated.
In addition, differential planar-mirror FPR antennas with fan beams are studied. The differential feeding enables direct integration with differential circuits and suppresses cross-polarized fields. The basic antenna structure consists of two parallel metallic plates that are perpendicular to the ground plane, similar to the single-fed planar-mirror FPR antenna. To reduce the side lobes, a modified antenna with a pair of parallel ridges on the side edges of the plates is introduced. Furthermore, to suppress backward radiation, another modified antenna with a ridge on the top of each metallic plate is proposed.
L-probe-fed FPR antennas with concave mirrors (cylindrical and spherical) are also investigated. The performances of these antennas are studied and compared with those of their planar-mirror counterpart. Cylindrical-mirror and spherical-mirror FPR antennas are more stable than the planar-mirror antennas. The formulae of the resonance frequencies for the proposed antennas are given to facilitate the design.
Finally, an inclined resonant slot is combined with an open cavity to produce circularly polarized (CP) fields. The open cavity has an FPR-like structure, which is formed by two parallel plates. Inside the cavity, two orthogonal modes are simultaneously excited by the inclined slot. A design procedure is described and demonstrated by the basic parallel-plate (PP) antenna with rectangular plates. However, the radiation pattern of the basic PP antenna is not axially symmetrical, and strong cross-polarized fields in near-boresight directions can be observed. The problems can be solved by replacing the rectangular plates with semicircular ones. The CP PP antennas can be designed remarkably easily because their polarization and impedance matching can be controlled independently.
In this study, the proposed antennas are simulated using the commercial software ANSYS HFSS. The reflection coefficients, radiation patterns, axial ratios, and gains of the antennas are studied and verified by our measurements. Parametric studies are also carried out to characterize the antennas.
| Date of Award | Aug 2012 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Kwok Wa LEUNG (Supervisor) |