Analysis and design of planar slot antennas for RFID applications using characteristic mode theory

Radio Frequency Identi cation (RFID) systems are widely used for identification and tracking of objects. The system consists of an active reader that illuminates the room and reads information from a passive tag antenna. These systems have been implemented in the LF (12 {13 KHz), HF (13 MHz), UHF (860 { 960 MHz) frequency bands. Most RFID tags in the LF and HF use simple loop variants to achieve magnetic coupling between the reader and the tag and have limited range (1 m). Improved communication range of up to 6 m can be achieved in the UHF band. Most systems in the UHF band make use of planar antennas with good radiation characteristics to achieve electromagnetic coupling between the tag and the reader. Thin form factor, placement-insensitivity, small size and good radiation characteristics are essential qualities of planar RFID tag antennas operating in the UHF band. Traditional half-wavelength microstrip antennas become too large for target objects which are small in size. Such antennas become too large for useat UHF RFID frequencies. However, reduction in size leads to degradation of bandwidth and gain of planar antennas. Slot antennas can be used to achieve miniaturization and achieve good radiation characteristics from sub-resonant length antennas. In addition, edge treatment in the form of serrations can be used to improve the bandwidth and radiation properties of thin planar antennas. Although serrations offer a simple technique to improve radiation characteristics of a microstrip antenna, there are no design guidelines or analytical tools available in the literature that help establish the correlation between serration geometry and radiation characteristics. In this research, a thin planar antenna with serrations and spiral slot is presented. The antenna assembly is analyzed for improvement in bandwidth and radiation properties using the theory of characteristic modes. The modal analysis of the planar antenna is done in three separate parts: serrated plate, rectangular slot and spiral slot. By appropriately selecting the serration geometry, the lower order characteristic modes can be combined to yield wider bandwidth in planar antennas. By selecting appropriate feed location based on characteristic mode analysis, optimal feed location for co-axial type feed mechanism can be determined. However, even serrated planar antennas can become too large for RFID applications if traditional coaxial-type feeding mechanism is used. Slots can be used as feeding mechanism and to achieve miniaturization of planar antennas. The behavior of slots on finite ground planes can be predicted by studying the modal behavior of slots in an in finite ground plane and using duality of magnetic and electric characteristic modes. The research presented here can be applied to design planar antennas in two parts: design of planar serrated antennas and design of slot antennas on finite ground planes. Based on characteristic mode theory, design guidelines are presented for improving the bandwidth and radiation characteristics of planar antennas by using serrations. Characteristic mode analysis is also used to chose the optimal feed location for exciting lower order characteristic modes in planar antennas. Also, design guidelines are presented for improving the bandwidth of rectangular slots in a finite ground plane. Additionally, characteristic mode theory based design guidelines are developed for designing multi-band spiral slot antenna in a finite ground plane. The design procedure presented here can be adopted to achieve miniaturization of planar antennas. Based on the design procedure presented here, planar slot antennas can be designed for different frequency bands and applications in existing RFID systems and other applications.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Electrical & Computer Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2020

Author dc:creator

• Sharma, Pallavi

Contributors dc:contributor

• Bernhard, Jennifer T.
• Franke, Steven J.
• Schutt-Aine, Jose E.
• Gong, Songbin

• Characteristic mode analysis
• characteristic mode theory
• slot antenna
• RFID tag antenna
• RFID
• spiral antenna
• planar spiral antenna
• spiral slot
• serrations
• edge-treatment

Statement dc:rights

• Copyright 2020 Pallavi Sharma

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/108286

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/108286