Applications of Optimization Techniques to Self-Structuring Electromagnetic Scatterers and Antenna Performance Enhancements
Date Issued
2012
Date
2012
Author(s)
Chen, Yen-Sheng
Abstract
In this dissertation, three innovative electromagnetic (EM) applications are
proposed to improve the efficiency and limitation of conventional employments. By
using the intelligence of optimization methodologies, including design of experiments
(DOE) and evolutionary algorithms, complex design processes and arduous synthesis
problems are simplified and solved, and the proposed applications exhibit powerful and
sophisticated capabilities which satisfy the original need.
The first application is a novel dual-antenna structure for passive radio-frequency
identification (RFID) tags. It is formed by two linearly tapered meander dipole antennas
that are perpendicular to each other and connected to the slightly modified tag chip. One
of the antennas is for receiving, while the other is for backscattering. The input
impedance of the receiving antenna is designed to be conjugate matched to the highly
capacitive chip impedance for the maximum power transfer. Meanwhile, the
backscattering antenna is alternatively terminated by an open or a short circuit to
modulate the backscattered field. By making the input impedance of the backscattering
antenna real-valued, the maximum differential radar cross section (RCS) may be
achieved leading to a longer read range and better reliability. With the aid of DOE, the
proposed dual-antenna structure is designed to fit within a compact area of 32.8 × 32.8
mm2 while keeping relatively low mutual coupling between the two antennas. The
impedance, receiving, and backscattering performances of the proposed dual-antenna
structure are measured and simulated, and they agree very well. Also, it is demonstrated
that the proposed dual-antenna structure outperforms the conventional single-antenna
tag design in every respect.
The second application is a competent antenna design tool based on the pixelized
design technique. Merely with only a roughly-formed solution domain, this pixelized
design tool is capable of automatically finding an antenna layout with performance
satisfying the design needs. The pixelized design tool integrates a full-wave simulator
and external optimization schemes, including various single-objective and
multiobjective evolutionary algorithms. The capability of multiobjective operations is
demonstrated by a multiple-input-multiple-output (MIMO) antenna system for handset
applications, where the impedance matching of each antenna should be optimized and
the mutual coupling between them should be minimized. In addition, an innovativeapproach for designing wide- and multi-band antennas within a small area is proposed
and incorporated into this tool. The proposed method is verified through a handset
antenna design, covering 698–960 MHz and 1710–2170 MHz. The simulated and
measured results confirm that the proposed method can find an antenna configuration
with satisfactorily wide bandwidth and outperforms the conventional approaches.
The third application is a self-structuring electromagnetic scatterer (SSES). The
SSES is the first intelligent reflective surface that can alter its electrical shape to fulfill
various operational objectives, such as RCS reduction or RCS enhancement. The SSES
template comprises segments of metallic thin strips interconnected via
voltage-controlled switches. By opening or closing the switches, the phase of the field
scattered by the strips changes, resulting in destructive or constructive interference in
the total scattered field. The RCS of the SSES can thus be controlled. An efficient
search algorithm based on the fractional factorial design of experiments (FFD) is
adopted to find a suitable switch configuration for the SSES system. A SSES prototype
was built and a series of RCS measurements were performed to demonstrate its
capability to adaptively control the RCS. It is shown that the bistatic RCS can be
significantly reduced in any specified direction and that the main beam maximum of the
RCS pattern can be enhanced and steered within an angular range of 30 degrees.
Subjects
Optimization techniques
Electromagnetic scattering
RFID
Antenna design
Type
thesis
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