Electronic Theses and Dissertations

Title

Reconfigurable Wideband Circulalry Polarized Microstrip Antenna for Wireless Applications

Author

Ahmed Khidre

Date of Award

2012

Document Type

Dissertation

Degree Name

M.S. in Engineering Science

First Advisor

Atef Z. Elsherbeni

Second Advisor

Alexander B. Yakovlev

Third Advisor

Fan Yang

Abstract

In this thesis, developments of rectangular microstrip patch antenna to have circular polarization agility with wideband performance, for wireless applications are presented. First, a new technique to achieve circularly polarized (CP) probe feed single-layer microstrip patch antenna with wideband characteristics is proposed. The antenna is a modified form of the popular E-shaped patch, used to broaden the impedance bandwidth of a basic rectangular patch antenna. This is established by letting the two parallel slots of the E-patch unequal. Thus, by introducing asymmetry two orthogonal currents on the patch are excited and circularly polarized fields are realized. The proposed technique exhibits the advantage of the simplicity inherent in the E-shaped patch design. It requires only slot lengths, widths, and position parameters to be determined. Also, it is suitable for later adding the reconfigurable capability. With the aid of full-wave simulator Ansoft HFSS, investigations on the effect of various dimensions of the antenna have been carried out via parametric analysis. Based on these investigations, a design procedure for a CP E-shaped patch is summarized. Various design examples with different substrate thicknesses and material types are presented and compared, with CP U-slot patch antennas, recently proposed in the literature. A prototype has been constructed following the suggested design procedure to cover the IEEE 802.11b/g WLAN band. The performance of the fabricated antenna was measured and compared with the simulation results for the reflection coefficient, axial ratio, radiation pattern, and antenna gain. Good agreement is achieved between simulation and measured results demonstrating a high gain and wideband performance. Second, a polarization reconfigurable single feed E-shaped patch antenna with wideband performance is proposed. The antenna is capable of switching from right-hand circular polarization (RHCP) to left-hand circular polarization (LHCP) and vice versa, with the aid of two RF PIN diodes that act as RF switches. The proposed structure which is simple; consists of a single-layer single fed radiating E-shaped patch and RF switch placed on each of its slots at an appropriate location. The design targets WLAN IEEE 802.11b/g frequency band (2.4- 2.5 GHz) as one example of the wireless applications. The idea is based on the first proposed design. In other words, if one of the switches is ON and the other is OFF, the two slot lengths will become effectively unequal and circular polarization will be obtained. If the states of the two switches are reversed, circular polarization with opposite orientation will be obtained at the same frequency band. Full-wave simulator Ansoft HFSS is again used for the analysis. Complete detailed DC biasing circuit of the switches for integration with the antenna is presented. Also, characterizations of the microwave components used in the biasing circuit are discussed. Antenna prototype has been fabricated and tested. Simulation results along with the measured one, for the reflection coefficient, axial ratio, radiation pattern, and antenna gain agree well, showing wide bandwidth and high gain for the two circularly polarized modes.

Concentration/Emphasis

Electrical Engineering

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