Theoretical Modelling on Substrate Integrated Impedance Surfaces Incorporated on Leaky Wave Antenna
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Date
2024
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Univrsity of Illinois at chicago (UIC)
Abstract
The operating frequency of electromagnetic devices, such as waveguides, cavities, resonators, and antennas, is generally determined by their physical dimensions. The purpose of this thesis is to propose a new concept of substrate-integrated impedance surface (SIIS), which is intended to enable the arbitrary control of the dimensions and operating cutoff frequency of electromagnetic waveguides, resonators, and antennas.
In this study, we validate the effectiveness of loading a substrate-integrated waveguide (SIW) with a capacitive SIIS (e.g., a blind-via array) to reduce its cutoff frequency. As a result, SIIS techniques may be useful in miniaturizing SIW-based components that operate at low frequencies. We adapt the non-local homogenization theory to build a solid approximation expression and derive an analytical model to assess and extract the surface capacitance of SIISs of different geometries using stochastic gradient descent (SGD) followed by the least square error (LSE) method to solve non-linear regression problems and fit exponential curves. To prove the concept, we conducted several experiments with SIIS-loaded SIWs set with different parameters to extract surface capacitance. As a result, we observe that the analytical and numerical results are in good agreement. Finally, we demonstrate that the capacitive SIIS incorporated with a half-mode substrate integrated waveguide (HMSIW) reconfigured as leaky wave antenna (LWA) expressed as HMSIW-LWA has the possibility to reconfigure and steer the radiation patterns. With the greatest hope, the research project findings may be of interest given the increasing importance of 5G millimeter-wave products and microwave quantum systems.
Description
Recently, capacitive substrate integrated-impedance surfaces (SIIS) have been successfully engineered to be integrated with antennas, where a one-dimensional array of blind vias embedded on substrate
integrated waveguides (SIW) provides additional reactive loading to change the characteristics of the antenna. SIIS has the possibility to both control the dimensions and interaction of EM fields inside materials, change the principal mechanism of operation, and select the appropriate performance. Therefore, SIIS has proven to be a potential candidate to realize miniaturized EM structures. For example, the bulky rectangular waveguides have a huge structure due to the demand for applications and operating frequencies, which could be easily replaced with substrate-integrated waveguides (SIW)
in addition to SIIS. To be more specific, the integration of SIW with SIIS slows changes in dispersion to reduce the bulky size of waveguides. This has been shown in proof, particularly in some published
works, and the results have already been taken into consideration as a direct urgency towards the deployment of antennas enabling them to operate in millimeter-wave wireless communication and
sensing systems. Although SIW-SIIS could save antenna size, it is evident that Half Mode Substrate-integrated Waveguide HMSIW-SIIS can provide an even smaller size, capturing on the above-mentioned advantages of SIW. However, unfortunately, the works published till date have not shown any analytical formulation that aids in predicting the equivalent impedance of capacitive SIIS and
extracting surface capacitance to make comparisons with numerical results. Moreover, the concept of reconfigurability using SIIS ignites ample interest in comparison with previous techniques. It has been
found that the variation in surface reactance could be used in beam steering, in contrast with existing methods to achieve the same integration of varactor diodes, changing material characteristics as in
ferrites. To overcome the challenges, this thesis attempts to address two major topics not yet published in the EM field: (1) the theoretical model of SIIS, which demonstrates a solid approximation of the
analytical model to predict the surface capacitance; (2) the reconfigurability concept of HMSIW loaded by SIIS.
Chapter 1 provides us with guidelines on SIW, its importance, possible applications, and future and current business trends, concluded by a comprehensive literature review on SIW.
Chapter 2 provides a significant demonstration comparing the theoretical model and numerical results to perfectly design the unit cell of SIW-LWA, which analytically enables the design of HMSIW. This
method indicates that our approach can be considered a roadmap in addition to further enhancement.
Chapter 3 introduces the concept of substrate-integrated impedance surface (SIIS). I apply homogenization theory, including the extraction of an equivalent model for SIIS and the study of mutual interconnection among meta-atoms. In this chapter, it has been verified that the proposed analytical result can intuitively predict the capacitive loaded-SIIS, interestingly drawing a relation to
cutoff frequency and dispersion, resulting in a successful fit with numerical curves and approximately minimizing the errors. This in turn results in an optimized HMSIW design with reduced size.
Chapter 4 proposes a new technique to integrate SIIS with HMSIW antennas. It has been expounded that the combination of HMSIW with SIIS results in a significant change in radiation pattern in addition
to adding liquid crystal (LC).
Chapter 5 adds valuable comments for both useful conclusions and future work considerations.
Keywords
substrate-integrated impedance surface (SIIS), substrate-integrated waveguide (SIW), stochastic gradient descent (SGD), least square error (LSE), leaky wave antenna (LWA)
Citation
IEEE