Improved designs of antennas, power dividers and antenna arrays using modified Gielis curves

• Main Author: Vignesh, Shanmugam Bhaskar
• Other Authors: Tan Eng Leong
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Electrical and electronic engineering::Antennas, wave guides, microwaves, radar, radio
• Online Access: https://hdl.handle.net/10356/144824
• Institution: Nanyang Technological University

Planar antennas have been extensively used in many wireless applications due to their compact size, easy design, and low fabrication cost. Some planar arrays need power dividers with filtering properties, especially in applications involving harmonic suppression. The electrical behaviour of any conductor patch or slot in the design of an antenna or power divider can greatly influence its performance. Hence, sectorially modified Gielis curves (SMGCs) can be used to improve the performance characteristics of antennas or power dividers or antenna arrays, such as increased impedance bandwidth, increased gain, and reduced lower cut-off frequency. The SMGCs will provide additional degrees of freedom (DOF) in the design of most structures. Firstly, the SMGCs are applied to enhance the performance characteristics of single element antennas. A CPW-fed monopole antenna with parasitic strips for unidirectional pattern is designed using SMGCs for the shape of the patch with planar reflector, to reduce the cut-off frequency while the parasitic strips are used to enhance the directivity. A broadband printed CPW-fed slot antenna is designed by using SMGCs for the shape of the slot and the patch, to provide additional paths for the surface current along the edges. This SMGC-based edge profile can influence the impedance matching. A planar mushroom-shaped wideband monopole antenna is designed using SMGCs as they are capable of generating complex shape profiles for the conductor patch conveniently and to improve the bandwidth. An ultra-wideband (UWB) double-sided printed bowtie antenna using SMGCs is designed to improve the surface current, which in turn improves the impedance matching and the radiation gain. Moreover, a design of a wideband bowtie slot antenna using SMGCs is discussed. The SMGCs used for the slot profile shows considerable improvement in the bandwidth and the gain when compared to conventional bowtie slot antennas. Secondly, the SMGCs are used in the feeding network, i.e., the power divider (PD) that feeds the antenna arrays. A center-fed four-way PD with wideband harmonic suppression is proposed with stubs that are designed using SMGCs to provide more DOF. The harmonic suppression is improved due to the introduction of open stubs, short stubs, and stub-loaded coupled lines using SMGCs. Of the two stages, the first stage is a center-fed two-way power divider with open and short stubs, while the second stage is a modified two-way Wilkinson power divider with stub-loaded coupled-line structures. Thirdly, the SMGCs are used in the designs of antenna arrays. They are applied in array or periodic structures such as frequency selective surface structures, one-dimensional periodic leaky-wave antennas, and grid-slotted patch antennas with linear and circular polarization. A three-dimensional bandstop frequency selective structure (FSS) based on a loop resonator is designed using SMGCs for the full and half loop resonator, to obtain a reduction in operating frequency when compared to a circular profile for a fixed unit cell size. A periodic leaky-wave antenna with SMGC for patch element is designed to enhance the operating bandwidth and the gain of the leaky wave antenna. A bidirectional linearly polarized grid-slotted patch antenna with SMGCs for patch elements can slightly reduce the lower cut-off frequency. A same-sense circularly polarized grid-slotted patch antenna with wide axial ratio bandwidth is designed by using SMGCs to form the patch elements. The patch elements are excited through flipped Z-shaped slots pair using a stripline feed to generate same-sense circular polarization with a wide axial ratio bandwidth in the category of same-sense antennas. Hence, SMGCs can play a significant role in improving the performance characteristics of antennas, power dividers, or antenna arrays, since the geometry of the conductor patches or slots can directly affect the surface currents.