Skip to Main Content
 

Global Search Box

 
 
 
 

Files

File List


PhD Dissertation_V5.pdf (20.71 MB)

ETD Abstract Container

Abstract Header

Novel Characteristic-Mode-Based Synthesis and Analysis Method for Reflectarray Antennas

Maalik, Abdul
http://orcid.org/0000-0002-5517-9250
http://rave.ohiolink.edu/etdc/view?acc_num=osu1593684814222685

Abstract Details

2020, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.
Characteristic Mode (CM) Theory has been receiving great attention over the past decade or so due to its ability to give physical insight into antenna design. There are great many methods, some very complex, and some not so, that are used in the design and analysis of antennas, but none gives better physical understanding of antenna radiation as CM theory does. The present research describes CM theory for periodic structures and then applies it to the analysis and optimization of reflectarrays in order to improve their performance. By defining a new frequency variable, the so-called generalized frequency, CM theory is applied to periodic structures. The generalized frequency embeds in it the periodic phase-shift between individual elements of the periodic structure. Modal tracking is then performed along generalized frequency. In order to apply CM theory to a quasi-periodic structure like reflectarray antenna, the total reflected field of reflectarray was decomposed into characteristic modal fields. Undesired mode(s) were then identified as the one that gave bad reflection-phase response and/or undesired radiation characteristics. The undesired modes were then be suppressed by reactive loading of the reflectarray. Since CM analysis is computationally an expensive task, it becomes prohibitive to analyze a large finite array using CM theory. In order to analyze a large finite reflectarray using CM theory, a zone-based approached is used, where zone 1 represents all the array elements except the outermost two rows (columns), zone 2 represents the elements in outermost two rows (columns) except the four corner-elements, and zone 3 represents the corner elements. CM theory for infinite structure is used to analyze zone 1, while CM theory for single element (or finite structure) is used to analyze zone 2 and 3. To validate that modal-decomposition of reflected field is correct, scattering pattern of a patch array is synthesized using the characteristic modal-patterns, and it matched quite well to the actual scattering pattern. A good reflectarray design requires that the phase-changing transmission-line-stubs should be impedance-matched to the connecting point on the reflecting (re-radiating) structure. Traditionally, the input impedance of reflecting structure is found by assuming the structure in direct-radiating mode (as is in phased-array). This input impedance only accounts for antenna modes. On the other hand, the scatterer or reflector has two kinds of modes generated in it, the antenna modes, and the scattering modes. The correct input impedance in case of reflectarray would be the one that takes into account both these modes. We present a method that computes the active input-impedance in scattering case. Transmission-Line Stubs are then designed based on this impedance, thereby reducing the spurious radiations and hence improving the radiation pattern of reflectarray. Finally, two different reflectarrays are designed to prove the validity of this research. First, a Ku-band patch-reflectarray is designed using conventional method. It is then analysed and optimized using CM theory. Improvement is seen in gain, side-lobe, and cross-pol performance. Pattern bandwidth of over 20% is achieved using single-layer design. Another array at X-band, based on a novel structure composed of hexagonal printed-loops and arranged in honeycomb fashion, is designed. Due to its inherent symmetry, this structure is a good choice for beam-scanning of reflectarray. A wide-angle scanning and a wide-bandwidth is achieved due to a combination of the novel structure and the CM theory. Scanning up to 600 in both principle and diagonal planes is demonstrated with acceptable scan-loss and cross-pol level, and the accompanying bandwidth is 33%. Both the arrays are fabricated and measured. Good agreement is found between simulated and measured results. This research will prove useful in the analysis and optimization of antenna arrays for the emerging 5G and satellite applications. CM-based analysis and optimization can prove good alternative to various brute-force optimization methods used in antenna array design.
Roberto Rojas (Advisor)
Robert Burkholder (Committee Member)
Patrick Roblin (Committee Member)
230 p.
Electrical Engineering; Electromagnetics
Characteristic Modes, Modal Analysis of Periodic Structures, Wideband Reflectarray, Wide-Angle Scanning Reflectarray, Characteristic-Mode-Based Optimization of Reflectarray, CM Analysis of Large Finite Array of Patches

Recommended Citations

Citations

  • Maalik, A. (2020). Novel Characteristic-Mode-Based Synthesis and Analysis Method for Reflectarray Antennas [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1593684814222685

    APA Style (7th edition)

  • Maalik, Abdul. Novel Characteristic-Mode-Based Synthesis and Analysis Method for Reflectarray Antennas. 2020. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1593684814222685.

    MLA Style (8th edition)

  • Maalik, Abdul. "Novel Characteristic-Mode-Based Synthesis and Analysis Method for Reflectarray Antennas." Doctoral dissertation, Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1593684814222685

    Chicago Manual of Style (17th edition)

osu1593684814222685
301
© 2020, all rights reserved.
This open access ETD is published by The Ohio State University and OhioLINK.