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https://hdl.handle.net/2142/19741
Description
Title
Cavity-backed T-fed slot antenna
Author(s)
Gilbert, Roland Arthur
Issue Date
1990
Doctoral Committee Chair(s)
Lo, Yuen T.
Department of Study
Electrical and Computer Engineering
Discipline
Electrical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Language
eng
Abstract
Cavity-backed slot antennas are experiencing a revival because of the ever-increasing need for low-profile and conformal antennas which have a low radar cross section out of their operating frequency bands. Like thin microstrip patch antennas, cavity-backed slot antennas typically have a narrow impedance bandwidth of 1 to 6 percent of center frequency, which limits their usage. A new method of feeding a thin cavity slot antenna with a stripline leading to a T-bar, which lies beneath or in the slot, greatly enhances the impedance bandwidth over a range of 10 to 30 percent depending on the slot width.
In the past, the design parameters for the T-fed slot antenna were obtained empirically. A computer model is developed in this thesis to provide a vehicle for analyzing the antenna's performance prior to fabrication. Since the antenna cavity is thin, there is a complex interaction between the T-bar, slot, stripline feed, and modes of the cavity.
In the antenna model, all of the cavity apertures are closed with a perfect conductor, and the fields there and on the T-bar are replaced with equivalent currents. The analysis is simplified by the superposition principle to obtain the total fields in the cavity by summing all the fields produced independently by each equivalent current source in the closed cavity. A method of moments approach is used to find the coefficients of the unknown equivalent sources by matching the fields in the cavity and the stripline to the appropriate boundary conditions. From these values the impedance of the antenna is determined. To verify the model, T-fed slot antennas were fabricated and measured at X-band and S-band. The calculated and measured values are compared.
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