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Title: Designing of Enhanced Gain Aperture Coupled Dielectric Resonator Antenna
Authors: Batra, Deepak
Supervisor: Sharma, Sanjay
Kohli, Amit Kumar
Issue Date: 4-Nov-2016
Abstract: Recent advances in the wireless communications have resulted in the development of antennas, which can be embedded into wireless products. For the last three decades, two classes of antennas i.e., the microstrip patch antenna (MPA) and the dielectric resonator antenna (DRA) have been under investigation for the modern wireless communication applications. MPA consists of a radiating patch on one side of the dielectric substrate with a ground plane on other side. MPAs are attractive due to their light-weight, low-profile planar configuration, conformability and low-cost as compared to the conventional antennas. These are highly compatible with embedded antennas in the handheld wireless devices, such as cellular phones and pagers etc. Another area, where the patch antennas have been used successfully, is satellite communication. MPAs radiate primarily because of the fringing fields between the patch edge and ground plane. For appropriate antenna performance, a thick dielectric substrate having a low dielectric constant is used to provide better efficiency, larger bandwidth (BW), and better radiation. But, such a configuration leads to a large antenna size. However, in order to design a compact MPA, higher dielectric constants are used, which are less efficient and result in narrower bandwidth. Moreover, MPAs have various limitations like narrow bandwidth, more metal losses (ohmic losses), low-gain, surface-wave excitation and poor polarization purity etc. Most of the limitations of patch antenna are removed in DRAs. Dielectric resonator antenna consists of the dielectric materials in its radiating patch (also called as dielectric resonators) on one side of the substrate and has a ground plane (metal) on the other side. These DRA configurations have received great interest in the recent years for its potential applications in the microwave and millimeter-wave communication systems. These have been widely used as a tuning component in the shielded microwave circuits, such as filters, oscillators and cavity resonators. With an appropriate feed arrangement, these can also be used as antennas, which offer efficient radiation patterns. These are easy to fabricate and offer more degree of freedom to control the resonant frequency as well as quality factor. These offer much wider impedance BW as compared to MPA because microstrip antenna radiates only through two narrow radiation slots, whereas DRAs radiates through its whole surface except the ground part. DRAs can have various three dimensional (3-D) shapes, but cylindrical, hemispherical, and rectangular DRAs (RDRAs) are the most commonly used. In this research work, we first propose a combination of the slot antenna and the dielectric resonator antenna, which leads to the design of a dual-band dielectric resonator antenna. The resonance of slot and that of dielectric structure gets merged to obtain wide bandwidth over which the antenna polarization and the radiation patterns are preserved. In this design, neither the miniaturization nor the efficiency is compromised. However, the main focus is on the gain as well as bandwidth of the proposed antenna, while preserving the antenna polarization and radiation pattern. The antenna structure is simulated using Ansoft high frequency structure simulator (HFSS). The simulation and experimental results are presented to demonstrate that the proposed RDRA resonates at two frequencies, 5.8Giga Hertz (GHz) and 8.0 GHz. It exhibits gain advantages of approximately 8.1 dBi and 9.05 dBi and the impedance BW of approximately 340 Mega Hertz (MHz) and 420 MHz, at the two resonance frequencies, 5.8 GHz and 8.0 GHz respectively. In addition, the effects of the size of slot on the radiation characteristics and antenna efficiency are also observed through simulation as well as experimentation. The proposed dual-band DRA has found applications in C- and X-band satellite wireless communication systems. RDRAs have enormous advantages over the conventional DRA structures. These offer a second degree of freedom, which is one more than cylindrical shape and two more than hemispherical shape, and these also facilitate the designer to have a greater design flexibility to achieve the desired profile and bandwidth characteristics for a given resonance frequency and dielectric constant. Therefore, these are preferred at millimeter-wave frequencies because of its simplicity in comparison to the cylindrical and hemispherical DRAs. However, the high-profile RDRAs with length-to-height ratio less than two have restricted low-profile applications, as these antennas exhibit low bandwidth as well as gain. We next propose a high-gain dual-band DRA mounted with horn, which provides higher gain in comparison to the conventional DRA. Horn is an aperture type of antenna, which is excited by the proposed DRA in the presented work. By using the horn (fabricated usingsilver metal), the gain of the conventional RDRA isincreased at the same resonance frequency, with reduced return loss. The simulation and experimental results are investigated to depict that the gain advantages of the proposed RDRA mounted with horn are approximately 8.95 dBi and 10.65 dBi and the impedance BWvalues are approximately 315 MHz and 375 MHz at the two resonance frequencies, 5.8 GHz and 8.0 GHz respectively. Therefore, the combination of surface mounted horn and DRA, results in the gain enhancement of approximately 0.85 dBi at 5.8 GHz frequency and approximately 1.6 dBi at 8.0 GHz frequency. However, the usage of horn results in increased cost of antenna fabrication. Therefore, other antenna configurations can also be investigated as an alternative. We further present the DRA using the electromagnetic band-gap (EBG) technology. The EBG technology is based on the total internal reflection phenomenon of photonic crystal, which is realized by using the periodic structures. EBGs combat surface-waves in the printed antenna boards. A significant amount of energy gets trapped into the substrate resulting in the unwanted surface-wave loss, which if controlled can boost the gain of antenna. However, EBG blocks the surface-waves from propagating in a certain band-gap. These do not allow the surface-waves to be reflected and interfere with desired radiated waves by grounding such spurious waves. The incorporation of EBG structure in DRA can substantially boost the gain and impedance BW. The simulation results are presented, to illustrate that the proposed hemispherical DRA resonates at 4.39 GHz, which provides a gain of 6.9 dBi and operates at a bandwidth of approximately 250 MHz. The simulation results also show that the hemispherical DRA with EBG structure provides improvement in the gain by approximately 3.7 dB (due to the suppression of related surface-waves). The bandwidth is also increased due to incorporation of EBG structure. The efficiency and the efficacy of the aforementioned DRAs can be utilized by incorporating these structures in the modern broadband wireless communication systems. Future work includes the testing and performance evaluation of proposed DRA structures in the practical multiple input multiple output (MIMO) and fourth generation mobile communication systems.
Description: PhD Thesis, ECED, TU, Patiala
Appears in Collections:Doctoral Theses@ECED

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