Graduation Year

2011

Document Type

Thesis

Degree

M.S.E.E.

Degree Granting Department

Electrical Engineering

Major Professor

Gokhan Mumcu

Keywords

AMC, Broadband Antenna, EBG, FSS, HIS

Abstract

Microstrip patch antennas are attractive for numerous military and commercial applications due to their advantages in terms of low-profile, broadside radiation, low-cost, low-weight and conformability. However, the inherent narrowband performance of patch antennas prohibits their use in systems that demand wideband radiation. To alleviate the issue, an existing approach is to combine multiple patch antennas within a log-periodic array configuration. These log-periodic patch antennas (LPMAs) are capable of providing large bandwidths (>50%) with stable broadside radiation patterns. However, they suffer from electrically large sizes. Therefore, their miniaturization without degrading the bandwidth performance holds promise for extending their use in applications that demand conformal and wideband installations.

In recent years, electromagnetic band gap structures have been proposed to enhance the radiation performances of printed antennas. These engineered surfaces consist of a periodic arrangement of unit cells having specific metallization patterns. At particular frequencies, they provide a zero-degree phase shift for reflected plane waves and effectively act as high impedance surfaces. Since, their band-limited electromagnetic field behavior is quite similar to a hypothetical magnetic conductor; they are also referred to as artificial magnetic conductors (AMCs). AMC structures were shown to allow lower antenna profile, larger bandwidth, higher gain, and good unidirectional radiation by alleviating the field cancellation effects observed in ground plane backed antenna configurations.

Previous research studies have already demonstrated that microstrip patch antennas can enjoy significant size reductions when placed above the AMC surfaces. This project, for the first time, investigates the application of AMCs to LPMA configurations. Specifically, the goal is to reduce the LPMA size while retaining its highly desired large bandwidth performance. To accomplish this, we employ various AMC surface configurations (e.g. uniform, log-periodic) under traditional LPMAs and investigate their performance in terms of miniaturization, bandwidth, gain, and radiation patterns.

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