This paper proposes a system for detecting and classifying realistic electronic devices in the presence of linear clutter objects based on a frequency-modulated con-tinuous-wave (FMCW) nonlinear radar. For classification, the proposed system utilizes statistical features of the time-segmented baseband signal envelope of the second har-monic responses from targets, which contain nonlinear co-efficients of targets, and a support vector machine (SVM) is used as the classifier. The system is validated using an ex-perimental apparatus in an anechoic chamber, and a mini-mum allowable SNR is set to ensure accurate target classi-fication in the presence of a linear clutter object. The trans-mit frequency band of the FMCW nonlinear radar used for the experiment is 3.0-3.2 GHz, and the receive frequency band is 6-6.4 GHz, which is the second harmonic of the transmit band. The experimental results show that the proposed system can detect and classify targets with a detection rate of 85.5 % and classification accuracy of 89.2%. The pro-posed system has the potential to provide an effective solution for detecting and classifying unauthorized electronic devices in various scenarios.

This paper presents the design and performance evaluation of a fully integrated digital phased array-based nonlinear radar system. The proposed system employs a bi-static structure, where the transmitter and receiver are physically separated. The transmitter operates at 3–3.2 GHz, while the receiver is designed to capture the second harmonic responses at 6–6.4 GHz. The system consists of 64 channels for both transmission and reception, enabling electronic beam steering through phase shift control. To enhance the beamforming accuracy, a novel transmitter calibration method utilizing an oscilloscope instead of a network analyzer was implemented. The method simplifies synchronization requirements while maintaining precise phase alignment. Performance evaluation of the radar system was conducted through experimental validation in both free-space and concealed conditions, using arbitrary commercial electronic devices as targets. The experimental validation results demonstrated an average range error of 32.3 cm with a range resolution of 37.5 cm. Additionally, multi-target detection was performed using beamforming techniques. In free-space conditions, the radar achieved accurate target localization with angular errors below 1°. In concealed conditions, nonlinear reflections introduced minor localization errors due to clutter. Despite these challenges, the system successfully detected multiple targets by employing a clustering method. To the best of our knowledge, the system presented here is the first demonstration of a fully integrated digital phased array-based nonlinear radar in the open literature.

As the applications utilizing harmonic backscattering continue to expand, the works on analyzing the radar cross section (RCS) through harmonic radar equation have also gained attention. Although various approaches exist for deriving harmonic RCS, there remains a gap in the theoretical derivation and experimental validation of the radar equation that accurately accommodates the specific harmonic responses of a given nonlinear target. This paper introduces a comprehensive radar modeling approach designed for practical harmonic radar system development. A mathematical model of reference harmonic radar system is proposed, which precisely takes into account the harmonic responses from a reference target engineered with a circuit simulation. To validate the effectiveness of this approach, two experimental scenarios are conducted, demonstrating that the proposed approach can be applied to harmonic radar models. Furthermore, this method enables the radar designers to systematically adjust radar parameters based on specific target characteristics and operational requirements.

This paper proposes a compact K-band dual-circularly polarized antenna that can be implemented on a non-linear tag based on third-order intermodulation (IM3) for bio-sensing applications. The proposed antenna has the characteristics of being low-profile and lightweight, with opposite circular polarizations (CP) between ports. The non-linear tag-based bio-sensing scenario utilizes K-band millimeter wave frequencies, which allows for compact non-linear tags for attachment to the body. Also, the proposed antenna features dual-CP, which are for the reception and re-radiation of incident transmit signals and the IM3 responses, respectively. To this end, a two-port traveling-wave series-fed patch array with coplanar proximity coupling is designed. Here, to minimize the size of the antenna, we use only four circular patch elements with a modified diamond-shaped microstrip feedline. Through simulation and measurement, we demonstrate that the proposed antenna has an axial ratio of less than 3 dB from 23.25 GHz to 24.1 GHz, with the reflection coefficients below −10 dB and port-to-port coupling below −15 dB. These results indicate the potential utility of the proposed antenna as a tag antenna for non-linear detection-based bio-sensing applications.

한국전자파학회논문지 (The Journal of Korean Institute of Electromagnetic Engineering and Science)

한국전자파학회논문지 (The Journal of Korean Institute of Electromagnetic Engineering and Science)