Design and investigation on substrate integrated waveguide fed dielectric resonator antennas for d-band applications.

Abstract

This thesis is devoted to the design of substrate integrated waveguide (SIW) fed dielectric resonator antennas (DRAs) for D-band applications. These antennas are necessary to establish high-speed communication links in wireless communication networks so as to support the emerging broadband applications such as the internet of things (IoTs), smart cities, virtual reality among others. Some of these applications demand for networks that can support high data rates and low latencies that exceed the capabilities of 5G networks. Consequently, communication systems are projected to operate in the millimeter wave (mm-wave) and terahertz (THz) frequencies. The D-band frequency spectrum is attractive for utilization in 6G communication systems owing to its vast bandwidths and is capable of very high data rates up to terabits per second (Tbps). However, this band suffers the limitations of short propagation distances due to the increased path losses at high frequencies. These effects can be mitigated by efficient antenna designs characterized by broad bandwidths and high-gains with low-loss interconnect networks. In addition, antenna structures with low profiles are attractive for ease of integration with other front-end devices. In this work, the substrate integrated waveguide fed dielectric resonator antenna is the preferred topology for the antenna design. Three different wideband antenna designs are presented and analyzed. The wideband operation of the presented designs is achieved through the higher-order mode (HOM) excitation of the dielectric resonator (DR) element to achieve multiple resonances in this frequency band. Adjacent resonances are merged together using various impedance matching techniques to enhance the antenna bandwidth. These designs investigate on different impedance matching techniques such as the use of defected ground structures (DGS), inductive metal vias (posts), cross-slots among others for antenna bandwidth enhancement and gain improvement. This work extends further the design of single element antenna to multiple-input multiple-output (MIMO) antenna design. A technique for mutual coupling reduction in closely packed antenna elements, which is based on metamaterial polarization rotation is presented and investigated. The investigation on the performance of the antennas is carried out using the commercial CST Microwave Studio full-wave electromagnetic simulator. The simulation results are analyzed in terms of the bandwidth, gain, radiation efficiency and radiation characteristics. The first design presents a SIW-DRA operating between 122.58 GHz and 139.51 GHz. The antenna exhibits multiple resonances at 123.64 GHz, 125.76 GHz, 127.4 GHz, 129.9 GHz, 134.9 GHz and 137.7 GHz. The design investigates the use of DGS and iristype discontinuity techniques for impedance matching improvement of a multi-resonant antenna. Simulation results show that the applied techniques are effective in merging together the adjacent bands of a multiband antenna for bandwidth enhancement. The antenna achieves a -10 dB impedance bandwidth of 13.4%, a peak gain of 12.3 dBi maximum directivity of 13.14 dBi and a high radiation efficiency of 84%. In addition, the antenna possesses stable broadband radiation patterns across the frequency band of operation. The second design presents a novel approach for the transformation of a dual-band SIW-DRA to a broadband antenna design. The design proposes systematic and sequential application of impedance matching techniques to improve the impedance matching in the stop band of the dual-band antenna without deterioration of its performance in the passbands. In the development of this approach, two preliminary designs are presented and investigated. The first preliminary design investigates the use of inductive metal vias in the SIW feeding structure for bandwidth enhancement. The effects of incorporating inductive via and DGS on the SIW feed structure of a dual-band antenna operating between 140.82 GHz - 145.24 GHz and 147.27 GHz - 151.02 GHz with a relatively narrow stop band of 2.03 GHz are investigated. The simulated results show that the inductive via and DGS effectively merge together the passbands of a dual-band antenna to achieve a wideband response of 138.27 GHz - 150.95 GHz. The second preliminary design presents a dual-band antenna operating between 126.95 GHz - 136.5 GHz and 139.67 GHz - 149.48 GHz in the lower and upper-frequency bands. The antenna is optimized for dual-band operation through the modification of the feeding slot to an I-shape to achieve a bandwidth 9.55 GHz and 9.81 GHz, representing fractional bandwidths of 7.2% and 6.78% in the lower and upper-frequency bands respectively. The impedance matching in the relatively wide stop band can be improved to merge together the passbands of the dual-band antenna to achieve a wideband response. This transformation is achieved through the use of inductive via, matching stub and DRA offset techniques in the dual-band antenna design. These techniques are systematically applied to the dual-band design and the parameters optimized to achieve a high-gain and wide bandwidth SIW-DRA. The antenna operates between 123.97 GHz and 152.13 GHz, with a -10 dB impedance bandwidth of 20.39% at the center frequency of 138.05 GHz, exhibiting a high gain of 11.67 dBi, directivity of 13.36 dBi and maximum total radiation efficiency of 79%. The radiation characteristics of the higher-order resonances excited at 124.38 GHz, 125.22 GHz, 130.28 GHz, 140.72 GHz, 141.59 GHz, 143.47 GHz, 149.7 GHz and 151.17 GHz show broadside radiation patterns. The research also focuses on the design of a wideband and low-isolation 2 × 2 SIWDRA based MIMO antenna. Initially, a single-element SIW-DRA is designed based on higher-order mode excitation with the antenna exhibiting multiple resonances. Different impedance matching techniques involving the embedding of inductive metal vias in the SIW feed, cross-slot feed and stepped-impedance sections are employed to minimize reflections and to achieve a good impedance matching between 136.68 GHz – 166.28 GHz. A -10 dB bandwidth performance of 19.5%, a gain of 11.06 dBi and a high radiation efficiency of 84% is achieved. Two antenna elements are linearly arranged with zero interelement distance in a 2 × 2 MIMO configuration to achieve high integration of antenna elements in a given space. A metamaterial-based decoupling network is investigated for isolation enhancement in the 2 × 2 MIMO configuration. The decoupling network is designed as a metamaterial polarization rotator (MTMPR) wall to rotate the polarization state of the electromagnetic wave transmitting through it. The MTMPR wall is integrated with the MIMO antenna for mutual coupling reduction. The Simulation results show that the MTMPR wall does not degrade the bandwidth performance of the MIMO antenna, and the presented design achieves an isolation performance greater than 21.16 dB across the entire bandwidth of operation. Besides the isolation, the antenna is analyzed by evaluating its diversity metrics. MIMO diversity metrics such as the envelope correlation coefficient (ECC), diversity gain (DG), mean effective gain (MEG), channel capacity loss (CCL) and the total active reflection coefficient (TARC) are evaluated. The MIMO design achieves an ECC of 0.008, DG > 9.9 between the two ports, MEG < 3 dB, TARC close to -10 dB for different phase angles of the input excitation and a CCL below 0.4 bits/s/Hz. The performances of the presented SIW-DRA designs are compared with published results and confirmed to meet the established minimum criteria for the appraisal of the presented designs. The results show that the presented designs are suitable for application in future 6G wireless systems.