Gradient index and metamaterial based circuits for microwave transceiver systems

• Main Author: Chandrasekaran, Karthik Thothathri
• Other Authors: Arokiaswami Alphones
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Electrical and electronic engineering::Antennas, wave guides, microwaves, radar, radio
• Online Access: https://hdl.handle.net/10356/156194
• Institution: Nanyang Technological University

Wideband radio frequency (RF) transceiver systems capable of 3D holographic imaging are suitable for multiple applications, including infrastructure inspection on infrastructure for non-destructive testing and evaluation, in biomedical applications to detect tumorstumours, and in surveillance/security applications. In this work, microwave passive components with enhanced performance characteristics ideal for realizing such transceiver systems are proposed. The performance characteristics of standard microwave passive guided-wave components and radiated wave components are enhanced by novel methodologies such as introducing gradient refractive index (GRIN) substrates and metamaterial-based concepts as double periodic composite right/left-handed (CRLH) structures. The passive guided-wave components that are designed include the following: GRIN Substrate Integrated Waveguide (GRINSIW) based directional coupler with complementary split-ring resonators (CSRRs) realizing enhanced bandwidth of 13.52% compared to conventional Substrate Integrated Waveguide (SIW) based directional couplers and improved stop-band rejection > 20 dB, GRINSIW based hybrid ring coupler with arbitrary power splitting ratio of 3 dB and 6 dB, square complementary omega (SCO) backed SIW based wideband phase shifter that has an operating bandwidth ranging from 8 to 14 GHz (55%) with a phase tolerance of ±5◦, and GRINSIW based wideband six-port receiver incorporating the wideband directional couplers, phase shifters, and power dividers. The radiated wave components designed to realize beamforming and beam-focusing include the following: Single periodic and double periodic composite right/left hand (CRLH) based wideband leaky-wave antenna capable of continuous backward to forward beam-scanning and a GRINSIW based non-uniform linear leaky-wave lens for beam-focusing. The double periodic leaky wave antenna has three distinct operating regions. The first RH leaky-wave region extends from 5.7 to 6.73 GHz with a scanning range extending from 30◦ to 65◦. The LH leaky-wave region extends from 7.6 to 10.37 GHz with a scanning range extending from −55◦ to 0◦ and gain > 5 dBi. The RH leaky-wave region extends from 10.37 to 13.87 GHz with a scanning range extending from 0◦ to 40◦ and gain > 8 dBi. The slope of the main beam direction in the LH region and RH region is 20.37(◦/GHz) and 28.57(◦/GHz). The non-uniform leaky wave lens is designed by introducing air-holes of varying radii to modify the permittivity of the medium so as to obtain the desired phase constant and leakage constant. It operates at f=10 GHz and achieves focusing with 90% radiation efficiency at the required spatial coordinates. The integration of various components realizes a wideband transceiver system, and the system is used for holographic 3D SAR imaging, and the results are reported. The guided wave components are integrated together with other active RF components and circuitry for control and data acquisition to realize a high dynamic range, low-cost, wideband transceiver system suitable for 3D holographic imaging. The system is used to perform 3D imaging using traditional synthetic aperture radar (SAR) algorithm and variations of SAR algorithm suitable for multi-layered media for different targets/scenarios, and the results are presented.