Open Access Dissertation
Date of Award
Electrical and Computer Engineering
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
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.
Alkhaldi, Nasser, "Design And Practical Implementation Of Harmonic-Transponder Sensors" (2019). Wayne State University Dissertations. 2136.