Date of Award

1-1-2012

Document Type

Campus Access Dissertation

Department

Electrical Engineering

First Advisor

Mohammod Ali

Abstract

The increasing demand for voice, video and data requires antennas in portable and wearable wireless devices with higher gain, lower exposure, and beam steering capabilities. While phased arrays can provide such solution their size, complexity and cost outweigh their potential benefits. The focus of this dissertation is to explore and utilize the concept of parasitic array radiators in order to allow beam steering in portable and wearable wireless devices. In this concept smaller footprint beam steering arrays can be developed using one or more driven antenna elements when accompanied by one or more parasitic elements. The beam steering angle is controlled by the feed impedances of the parasitic elements. This control is achieved using varactor diodes and PIN diode switches. The variation in the inter-element spacing and the feed impedance along with proper element geometry selection are key design parameters which are investigated in this work both in free space and in the presence of an anatomical human head and body model.

First, the limitations of conventional fixed beam antennas are elucidated by studying their exposure effects on the human head model. Second, a parasitic antenna array operating at 1900 MHz is designed, optimized, and developed for a handheld terminal where varactor diodes are used to steer the array beam within a specific angular region. Third, a body wearable beam steering antenna array is studied, designed, and implemented at 2450 MHz using PIN diode switches. The analyses and design methods are developed which identify the dependency of the various constituent elements on the bandwidth, gain, and beam angles. This particular array shows a peak gain of 8 dBi, a steering angular range of 65 degrees and electromagnetic exposure reduction of more than 70 percent. Finally, a body wearable 900 MHz parasitic antenna array is introduced which provides a peak gain of 5.7 dBi and an azimuth plane steering angular range of 90 degrees. The design methodology is developed to determine the effective capacitance terminations for beam steering at different angles. Array prototypes are fabricated and tested using copper, conductive fabric and conductive threads both in free space and in the presence of a human body.

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