Access Type

Open Access Dissertation

Date of Award

January 2019

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Electrical and Computer Engineering

First Advisor

Pai-Yen Chen

Abstract

Harmonic radar is a nonlinear detection technology that transmits and receives

radio-frequency (RF) signals at orthogonal frequencies, so as to suppress the undesired

clutters, echoes and electromagnetic interreferences due to multipath scattering.

Its implementation generally comprises a nonlinear tag (i.e, a harmonic transponder),

which picks the interrogation signal at specific fundamental frequency (f0) and converts

it into a high/sub-harmonic signal (nf0). Such a technology has been successfully

applied to tracking small insects and detection of electrically-small objects in

the rich-scattering environment. Similarly, a harmonic sensor is used to interrogate

electrically-small and passive sensors, of which the magnitude and peak frequency

of output harmonics (e.g., second harmonic) are functions of the parameter to be

sensed. A harmonic tag or sensor comprises one or multiple antennas, a frequency

modulator, a sensor, a microchip and matching networks. Here, we propose and

experimentally validate compact, low-cost, low-profile, and conformal hybrid-fed microstrip

antennas for the harmonics-based radar and sensor systems. The proposed

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microstrip antennas are based on a simple single-layered and hybrid-feed structure.

By optimizing the feed position and the geometry of microstrip patch, the fundamental

mode and particular higher-order modes can be excited at the fundamental

frequency and the second harmonic. We have derived the analytical expressions for

calculating the antennas’ resonant frequencies, which have been verified with numerical

simulations and measurements. Our results show that the proposed hybrid-feed,

single-layered microstrip antennas, although having a compact size and a low profile,

can achieve descent realized gain (1.2 – 3.5 dB), good impedance matching (return

loss < -15 dB), high isolation (<-20 dB), and favorable co/cross-polarization properties.

The proposed microstrip antennas may benefit various size-restricted harmonic

transponders used for harmonic radars, harmonic sensors, medical implants, passive

radio-frequency identification (RFID), and internet-of-things (IoT) applications.

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