Investigation On Wideband High Gain Fabry-Perot Resonator Antennas

With the development of modern wireless communication technologies, the demand forantennas with specific performances is becoming more and more stringent. Among them,wideband high gain antennas or arrays have attracted lots of attentions in the worldwide. TheFabry-Perot resonator antenna is a kind of highly directive antenna which is based on theelectromagnetic band gap (EBG) technique. A conventional Fabry-Perot resonator antenna isformed by placing an EBG structure as a partially reflective surface (PRS) at a proper distancefrom a primary radiator with a ground plane. It has several merits, such as ease of fabrication,configuration simplicity, and achieving a high radiation gain without a complexbeam-forming network which is essential in an array system leading to serious metal anddielectric losses. However, an inherently narrow bandwidth (including the impedancebandwidth and the gain bandwidth) due to narrowband characteristics of both the resonantcavity and the EBG structure severely inhibits its use for many applications. In thisdissertation, to overcome this disadvantage, numerous investigations are carried out andseveral approaches are proposed for the design of wideband high gain Fabry-Perot resonatorantennas. The major contributions of this dissertation are listed as follows:1. The Fabry-Perot antenna is analyzed with a ray-tracing model and the mainparameters are concisely derived which are helpful for understanding the operating principle.Then impacts of characteristics of the PRS and structure dimensions on the performance ofthe resonator antenna are carefully studied. Moreover, slot-coupled patch antennas areselected to feed the resonator antenna, and it is air-loaded between the patch and the slot tosuppress the excitation of surface waves, which can be introduced to the cavity and degradethe performance of the resonator antenna.2. Instead of using the method of full-wave simulation, the transmission-line theory andSmith Chart are applied in the design of the PRS. EBG structures are firstly modeled asequivalent circuits and then analyzed with Smith Chart. This method greatly simplifies thedesign process of the PRS and provides a better understanding of the physical insight.3. The condition for the Fabry-Perot resonator antenna to produce a wideband resonanceis obtained by analyzing the ray-tracing model. A new EBG structure is proposed as the PRS,which is constructed by using two layers of dielectric slabs with electrical thicknesses of1/4dielectric wavelength and1/2dielectric wavelength, respectively, and can approximatelysatisfy the wideband-resonance condition. This EBG structure can be used to enhance the gain bandwidth and impedance bandwidth of the Fabry-Perot resonator antenna, which is validatedby a practical antenna design and corresponding experiments.4. An approach of using electrically thin dielectric slabs to realize wideband high gainFabry-Perot resonator antennas is proposed. In traditional Fabry-Perot resonator antennadesigns, thicknesses of the substrates constructing the PRS are required to be around1/4dielectric wavelength or more. This limitation seriously reduces the design flexibility andincreases the cost because there are not a variety of thicknesses to be selected, and substrateswith large thicknesses are not easily available, particularly in low frequencies. To avoid thisdrawback, an approach is proposed to realize wideband high gain Fabry-Perot resonatorantennas with electrically thin dielectric substrates while keeping the enhanced gainbandwidth and impedance bandwidth.5. Printed double-layered frequency selective surfaces (FSSs) are applied to the design ofwideband high gain Fabry-Perot resonator antennas. To understand the working principle ofthe FSS structure well, it is further modeled as an equivalent circuit and analyzed using SmithChart step by step. The design of printed FSS is more flexible. It replaces the EBG structureconstructed by dielectric substrates as a PRS, generally eliminating the effects of dielectricconstants and thicknesses of the substrates on the performance of the Fabry-Perot resonatorantenna, and greatly increasing the degree of freedom of the design. Through theoreticalsimulations and experimental studies, the design method has been well demonstrated.Summarily, this dissertation presents a series of work aiming at improving the bandwidth,simplifying the design procedure, increasing the applicability of wideband high gainFabry-Perot resonator antennas.