Graduation Year

2025

Document Type

Thesis

Degree

M.S.E.E.

Degree Name

MS in Electrical Engineering (M.S.E.E.)

Degree Granting Department

Electrical Engineering

Major Professor

Stavros Vakalis, Ph.D.

Committee Member

Jing Wang, Ph.D.

Committee Member

Gokhan Mumcu, Ph.D.

Keywords

Antenna, Diode, Gain, Nonlinear, Radar

Abstract

Passive harmonic Radio Frequency (RF) tags are highly advantageous compared to theiractive counterparts due to their ability to operate effectively in environments that are cluttered or where access to the tag for battery maintenance is challenging, dangerous and/or time consuming. They are also resistant to the local oscillator (LO) phase noise in radar applications where the doppler frequency from slow moving targets is buried beneath the noise. One of the major constraints of passive harmonic RF tags, however, lies in their operating range and the significant amount of power required to overcome the conversion loss and activate the nonlinear device responsible for transmitting the harmonic of the incident signal.

This work introduces the concept of harmonic RF tag repeaters as a solution to extend the tag’s range while simultaneously increasing the power incident on the tag, which is necessary to activate the nonlinear device that generates the harmonic signal. This way, harmonic tags that are concealed can be excited from a far enough distance without transmitting enormous amount of power from the tag interrogator. The study employs a 2.4 GHz and 4.8 GHz bi-directional repeater, which is designed to amplify both the fundamental and harmonic signals between the transceiver source and the RF tag. The experimental results demonstrate that by incorporating repeaters, the range of the passive harmonic tag can be enhanced by a factor of 3 to 4, increasing from 2 meters to a minimum of 6 meters with just one repeater. Furthermore, the power required to activate the nonlinear device also improves as the distance increases, showing the effectiveness of the repeater in optimizing tag performance.

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