Advanced RF/microwave Systems for Sensing and Communication Applications
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As the fifth generation (5G) and beyond networks as well as the Internet-of-things (IoT) continue to expand and become more prevalent in various industries, we will encounter connected devices almost everywhere. Consequently, antennas will be deployed in diverse indoor and outdoor environments. To pave the way for a new sensing and communication technology paradigm, it is necessary to equip antennas with additional sensing capabilities without compromising their wireless communication performance. Therefore, developing an advanced dual-functional system that can function as a wireless communication and a sensing device simultaneously, without interfering with each other, has become increasingly critical. Based on the above motivation, this Ph.D. work on advanced Radio frequency (RF)/microwave sensors for sensing and communication application is divided into three parts: The first part focuses on improving planar microwave sensors’ sensitivity and sensing ability; the second part focuses on integrating sensing and communication performance in a single-port standalone system; the third part deals on improving isolation of Multiple-Input Multiple-Output (MIMO) systems and its use for sensing applications. For the first part, different dielectric characterization techniques are investigated focusing on improving the sensitivity of a planar resonator by concentrating more electric field on the resonator. Then, an additional sensing parameter is proposed that can enhance the sensing abilities of microwave sensors by characterizing the dielectrics based on the frequency distance of the proposed sensor in the presence of a material under test (MUT). The resonance method is used to characterize materials based on the relative resonance frequency shift, which is inversely proportional to the unloaded resonance frequency (i.e., the sensor without MUT). Therefore, any variations in the unloaded resonance frequency caused by external factors can result in incorrect material characterization. The proposed additional parameter can provide an alternative solution to characterize the material without requiring the information on unloaded resonance frequency, saving time and power. In the second part, the main focus is kept on incorporating sensing and communication abilities in a single standalone system. This is motivated by the fact that incorporating dual functionality in an antenna system can enable a new paradigm. In addition, it also reduces the hardware resources used when compared to individual sensing and communication system. We started with designing a microstrip-based low-pass filter (LPF) and a high-pass filter with a different cut of frequencies. These filters are connected at the output paths of a T-junction to create the frequency selective multipath filter (FSMF). The FSMF has a common input port and two output ports. The purpose of the FSMF is to accommodate different RF/microwave devices at its output ports. The lumped-equivalent circuit model of the FSMF is designed using Keysight ADS. The microstrip model of FSMF is further optimized for better performance. To evaluate the performance of the FSMF, in the first set-up, a communicating antenna and a two-port resonator-based microwave sensor are connected at the output ports of the FSMF. The microwave sensor is used for the dielectric characterization of ethanol and water with gasoline. The proposed microwave sensor characterizes the MUTs based on the frequency distance of the reflection zeros. The numerical modeling of the frequencydependent properties of the binary mixtures is created using the Maxwell-garnett formula. A communicating antenna and antenna sensors are connected at the output ports of the novel FSMF in the second set-up. The communication antenna is designed to operate at 2.45 GHz, while the antenna sensor is designed to work over 4.5 GHz. The antenna sensor is tested for different dielectric with permittivity from 2.2 to 6.15. In addition, the proposed antenna sensor is also tested for ice and water detection. The proposed design shows that dual-functionality for sensing and communication can be achieved with the incorporation of the FSMF. The third part focus on the isolation enhancement of MIMO system and their use for sensing applications. Different parameters for evaluating the performance of a MIMO system are discussed. Design challenges associated with the MIMO systems are investigated, and the improvement of isolation using suitable techniques in a MIMO system is presented. A four-port multi-functional filtenna (antenna with filter) system with an isolation filter to reduce the mutual coupling is designed for sub-6 GHz applications. The proposed system includes a dual-operational filter in its feedline. In the first operation mode of the filter, the proposed system acts as a dual-band MIMO system; in its second operation mode, it acts as a single-band MIMO system. The proposed system is fabricated on Rogers RO 4003C printed circuit board. The measured results show good agreement with the simulations. Another 8-port quad band MIMO antenna system for mobile terminal applications is also presented. The design includes eight radiating elements placed in doublefolded symmetry and excited using offset-fed coaxial ports for multiband operation in the sub-6 GHz frequency range. An open-stub line-based isolation enhancement technique is used to improve the isolation between the radiating elements. The proposed approach can enhance the isolation between any two ports and can be repeated to reduce mutual coupling between several other ports. Hence, it can be suitable for mutual coupling reduction in an n-port MIMO system. Finally, using the isolation enhancement techniques mentioned before, a two-port MIMO antenna sensor is designed to identify and classify different liquids irrespective of their water contents. For numerical modeling of the liquids, their frequencydependent electrical properties are used. As compared to resonator-based sensors, the MIMO antenna sensor could be an alternative way with better penetration capabilities of the fields into the liquid material under test. The results achieved in this PhD work will pave the way for dual-functional antenna systems with sensing and communication capabilities. Playing a significant role in different applications, including environmental monitoring, dielectric characterization, biomedical applications, etc.