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NOVEL METHOD TO CONTROL ANTENNA CURRENTS BASED ON THEORY OF CHARACTERISTIC MODES
Elghannai, Ezdeen Ahmed

2016, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.
Characteristic Mode Theory is one of the very few numerical methods
that provide a great deal of physical insight because it allows us to determine the
natural modes of the radiating structure. The key feature of these modes is that the
total induced antenna current, input impedance/admittance and radiation pattern
can be expressed as a linear weighted combination of individual modes. Using this
decomposition method, it is possible to study the behavior of the individual modes,
understand them and therefore control the antennas behavior; in other words, control
the currents induced on the antenna structure.
This dissertation advances the topic of antenna design by carefully controlling the
antenna currents over the desired frequency band to achieve the desired performance
specifications for a set of constraints. Here, a systematic method based on the Theory of Characteristic Modes (CM) and lumped reactive loading to achieve the goal
of current control is developed. The lumped reactive loads are determined based on
the desired behavior of the antenna currents. This technique can also be used to
impedance match the antenna to the source/generator connected to it. The technique is much more general than the traditional impedance matching. Generally, the
reactive loads that properly control the currents exhibit a combination of Foster and
non-Foster behavior. The former can be implemented with lumped passive reactive components, while the latter can be implemented with lumped non-Foster circuits
(NFC).
The concept of current control is applied to design antennas with a wide band
(impedance/pattern) behavior using reactive loads. We successfully applied this novel
technique to design multi band and wide band antennas for wireless applications. The
technique was developed to match the antenna to resistive and/or complex source
impedance and control the radiation pattern at these frequency bands, considering size and volume constraints. A wide band patch antenna was achieved using
the developed technique. In addition, the technique was applied to multi band wire
less Universal Serial Bus (USB) dongle antenna that serves for WLAN IEEE 802.11
a/b/g/n band applications and Radio Frequency Identification (RFID) tag antenna
for 915MHz band applications with superior performance compared to previous published results.

This dissertation also discusses the total Q of an antenna from the CM standpoint.
A new expression as well as additional physical information about each mode's
individual contribution to the total antenna Q are provided.
Finally, the theory is used to an analyze the antenna in both radiation and/or
scattering modes. In the antenna scattering mode, the field scattered by an antenna
contains a component that is the short circuit scattered field, and a second component
that is proportional to the radiation field. In this dissertation, an analytical study
of this phenomena from the CM standpoint is performed aiming to shed some light
on antenna scattering phenomenon where additional physical insight is obtained and
thus used to reach desire results.
Roberto Rojas, Prof (Advisor)
Fernando Teixeira, Prof (Committee Member)
Robert Burkholder, Prof (Committee Member)
162 p.

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Elghannai, E. (2016). NOVEL METHOD TO CONTROL ANTENNA CURRENTS BASED ON THEORY OF CHARACTERISTIC MODES. (Electronic Thesis or Dissertation). Retrieved from https://etd.ohiolink.edu/

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Elghannai, Ezdeen. "NOVEL METHOD TO CONTROL ANTENNA CURRENTS BASED ON THEORY OF CHARACTERISTIC MODES." Electronic Thesis or Dissertation. Ohio State University, 2016. OhioLINK Electronic Theses and Dissertations Center. 23 Nov 2017.

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Elghannai, Ezdeen "NOVEL METHOD TO CONTROL ANTENNA CURRENTS BASED ON THEORY OF CHARACTERISTIC MODES." Electronic Thesis or Dissertation. Ohio State University, 2016. https://etd.ohiolink.edu/

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Full text release has been delayed at the author's request until December 19, 2017