Third-order nonlinear radar design and Its applications

Date

2020-12

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Abstract

The electronic circuits exhibit nonlinear behavior due to the presence of nonlinear components such as diodes, transistors, etc. This nonlinear behavior is very important for circuit operation. A mixer which is one of the most important building blocks of the radar utilizes the nonlinear behavior for up/down conversion. Similarly, the nonlinear behavior of the diode finds its use for rectifying signals. This dissertation discusses the design of nonlinear radar systems and the system validation of the nonlinear radar for short-range localization, clutter rejection, and life tracking. In the traditional tracking system, the clutter surrounding the target shows up in the measurement result, making it difficult to distinguish the clutter from the target. Compared to the traditional tracking system, the nonlinear based tracking system, the clutter which is mostly naturally occurring objects can be suppressed, filtered out, and discarded in the measurement result based on the nature of their backscattered response. The challenges faced while designing the nonlinear radar are the negative impact of high power density on the target, maintaining high linearity, and dynamic range of the receiver to capture weak nonlinear responses backscattered by the target. Many groups have designed the nonlinear radars based on 2nd order harmonic response. In these radars, a single frequency tone was transmitted out and their 2nd order harmonic response was utilized for detecting the nonlinear targets. This dissertation discusses the design of two different nonlinear radars i.e., 3rd order harmonic based and 3rd order intermodulation based nonlinear radars. A portable nonlinear radar, utilizing 3rd order harmonic response was designed and measurements were performed to validate the clutter rejection ability of the radar. Other than 3rd order harmonic response, 3rd order intermodulation response was also utilized for clutter motion rejection, vital signs monitoring, and target localization. The 3rd order intermodulation based nonlinear radar was operated in Doppler, frequency-shift-keying (FSK), and frequency modulated probing signal (FMPS) modes to various applications. In the Doppler mode, the motion generated by the target was recorded while the motion generated by the clutter was rejected. In this mode, the weak vital sign signals also were amplified. In the FSK mode, the localization of the target was performed based on the phase difference of the Doppler frequency. In the FMPS mode, the target localization and ranging were performed in the presence of large naturally occurring clutter objects. The dissertation also discusses the potential utilization of 3rd order intermodulation response for device authentication purposes.


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Keywords

Clutter rejection, Harmonic radar, Intermodulation radar, Nonlinear radar, Third order nonlinear response, Target tracking, Vital signs monitoring

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