In this paper, a compact wideband dual-decoupling technique is proposed for wideband microstrip patch antennas (WMPAs) at the X band. The wideband decoupling property is achieved by integrating the ...defected ground structure (DGS) and the coplanar inductance on the ground plane and patch layer, respectively. To validate the feasibility of the proposed method, both the aperture-coupled and probe-fed WMPAs with the proposed novel decoupling scheme are simulated, fabricated, and measured, respectively. An equivalent circuit and characteristic mode analysis (CMA) of this wideband decoupling scheme are developed to provide physical insight succinctly. Experimental results demonstrate that the poor isolation of the two proposed antennas has been improved from 6 dB to better than 20 dB with an extremely close edge-to-edge distance of 1 mm (0.033 λ 0 ). The achieved decoupled bandwidths are up to 17.6% and 22.2 % for the aperture-coupled and probe-fed schemes, respectively. In addition, the proposed method has also been extended to the decoupling of multi-element antenna arrays, demonstrating its potential for large-scale wideband massive multiple-input and multiple-out (MIMO) applications.
The motion sensing capability of millimeter-wave radar is significantly contingent upon its operating frequency. However, conventional techniques do not allow frequency modification once the radar ...hardware is completed. In this article, a novel frequency-reconfigurable technique is proposed to enable the operating frequency reconfiguration without any hardware modifications, enhancing the radar's capability to perceive displacement motions across various scales. This technique splits frequency-modulated continuous-wave (FMCW) beat signals into multiple sub-FMCW signals, yielding pairs of quadrature signals that are similar to those in continuous-wave radars. These quadrature signals are subsequently synthesized to quadrature signals at a new operating frequency. For weak motions of deep subwavelength scale, the proposed technique improves the detection sensitivity by reconstructing equivalent quadrature signals at a higher operating frequency, such as from 60 up to 480 GHz. For large-scale motions, this technique surpasses the radar's velocity limit by reconstructing that at a lower frequency, e.g., 60-1 GHz. Simulation results and theoretical analysis demonstrate the superiority of this technique for motion sensing. Experiments were also carried out to validate this technique in detecting the weak deep subwavelength, large-scale mechanical vibrations, and action gestures. Experimental results indicate that this technique exhibits approximately a three times accuracy improvement in detecting weak motions and about ten times accuracy improvement in detecting large-scale motions compared to the conventional technique.
Robust contactless Doppler cardiogram (DCG) detection in practical scenarios encounters challenges arising from radar hardware performance limitations and signal processing effectiveness. In this ...work, through an analysis of IQ mismatch signals, we proposed a novel vectors analytic demodulation (VAD) method, which employing the original radar signal to generate four basis vector signals, to linearly obtain the target's differential displacement signal. Simulation experiments confirm the efficacy of VAD algorithm in achieving efficient linear phase demodulation under IQ mismatch and time-varying dc offset, surpassing the performance of existing linear demodulation algorithms. Subsequently, based on the demodulated differential displacement signal, we develop a DCG-based QRS and T wave (DCG-RT) detector to enhance the characteristic waveforms corresponding to QRS-and T-wave for automatic cardiac timing like QRS-wave to QRS-wave (RR) interval and QRS-wave to T-wave (RT) interval calculation. This algorithm achieves easily identifiable cardiac feature waveforms with minimal computational resources. Using a 24-GHz Doppler radar and medical device, the synchronous acquisition experiments were conducted on five subjects. The comparative analysis of the enhanced signals extracted by the algorithm with PCG, ECG, and other signals reveals a remarkable 98% accuracy in cardiac timing detection.
In short-range sensing, the frequency-modulated continuous-wave (FMCW) radar is subject to the leakage between the transmitter (Tx) and the receiver (Rx) and the stationary clutter reflections, which ...are difficult to deal with due to the proximity to the target. The proximity ghost image may not only interfere with the target but also pose limitations on the radar performance, such as the degradation of the signal-to-noise ratio (SNR). This article proposes a novel hybrid analog and digital compensation techniques, which mitigates the leakage and the stationary clutters by compensating with the prestored anti-interference signals in both analog and digital domains at the intermediate-frequency (IF) stage. A novel modulation signal-based synchronization (MBS) technique is developed to align the real-time IF signal with the anti-interference signal during the compensation process. By significantly suppressing both the Tx-Rx leakage and the stationary clutters, the proposed technique greatly improves the signal-to-interference ratio (SIR) of the IF beat signals and makes possible the detection of targets with weak reflections. Moreover, the analog compensation enables the full use of the dynamic range of the analog-to-digital converter (ADC), which will reduce the impact of quantization noise and, thus, improve the SNR. Experiments have been carried out to validate the performance of the proposed technique in leakage compensation, weak target detection, stationary clutter compensation, and gesture sensing. The experimental results show that the SIR and the SNR have been improved by around 38 and 10 dB, respectively.
In this article, a displacement motion sensing technique is proposed for Doppler radar with low-intermediate frequency (IF) architecture, which combines asynchronous bandpass sampling with a phase ...extraction (PE) technique. Asynchronous bandpass sampling is leveraged to reduce the sampling rate and ease the demands on analog-to-digital converters (ADCs). The PE technique can easily recover the signal phase information without the need for synchronization circuitry or carrier compensation circuitry, compared to the existing low-IF demodulation techniques. Moreover, the proposed technique is able to extract the phase evolution of a moving target from overmodulated IF signals without any distortion, which is superior to the state-of-the-art methods such as the envelope detection (ED) technique. The proposed extended PE technique eliminates the phase drift or jumps present in the PE process by using a multiperiod segmentation method. Experimental results demonstrate that the proposed technique can recover small displacement motions more accurately and has better sidelobe performance than the ED technique. For overmodulated IF signals caused by large displacement motions, the proposed technique can accurately extract the phase trajectory without distortion. Additionally, experiments demonstrate that the proposed technique can successfully capture physiological signals, such as respiration and heartbeat, while reducing the sampling rate to only 100 Hz for an IF of 1050 Hz. Finally, the effect of the extended phase extraction technique in eliminating phase drift or jumps is also verified by theoretical analysis and comparative experiments.
Noncontact vital sign detection based on microwave sensing has attracted much interest for its important application potential in many fields, especially in the field of healthcare. However, robust ...and accurate heart rate (HR) tracking remains a challenge due to the tricky and universal respiration harmonic interference in real scenarios. In this article, a novel method, called differential enhancement (DE), was proposed, which can effectively eliminate the effects of the respiration harmonic interference on HR estimation, including the likely adjacent harmonic interference. The basic idea underlying our proposed method is that the differential operation can significantly enhance the heartbeat components, especially high-order heartbeat harmonics, and it is very useful to locate the true value of HR by combining with the autocorrelation-based periodicity extraction technique. The detailed procedures for performing the DE method were described, which can be simply implemented and have low computational complexity. In addition, a rigorous mathematical analysis was provided for demonstrating the robustness and accuracy of the algorithm. Experimental results with various scenarios validated the performance of the proposed method, and we investigated the HR variability (HRV) monitoring capability of the DE method with a short sliding window length.
Radar interferometry is widely used for detecting versatile displacement motions. The conventional techniques for motion extraction depend on the quadrature <inline-formula> <tex-math ...notation="LaTeX">I/ Q </tex-math></inline-formula> signals, and the proper calibration of the <inline-formula> <tex-math notation="LaTeX">I/ Q </tex-math></inline-formula> signals is a necessary step to ensure accurate motion detection. However, the calibration process and the <inline-formula> <tex-math notation="LaTeX">I/ Q </tex-math></inline-formula> architecture inevitably add up to the system complexity. In this article, a novel single-channel-based phase demodulation (ScPD) technique is proposed to reconstruct the precise phase information of the displacement motions, which not only employs only one single receiver channel but also eliminates the <inline-formula> <tex-math notation="LaTeX">I/ Q </tex-math></inline-formula> signals calibration. In addition, the proposed technique is immune to the phase ambiguity issue. To detect versatile motions with both regular and irregular patterns, approaches including envelope unwrapping, null point rejection, and outlier elimination are proposed and integrated to increase the robustness of the proposed technique. Both simulation and experiments were carried out to validate the proposed technique. The experimental results show that the proposed ScPD technique can obtain both periodic and irregular motions with high accuracy of a root mean square error (RMSE) of 0.011 mm and strong robustness to low signal-to-noise ratio (SNR) and <inline-formula> <tex-math notation="LaTeX">I/ Q </tex-math></inline-formula> mismatch with an RMSE of 0.015 mm. Moreover, the proposed technique is superior in detecting subtle motions, e.g., 3-<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula> displacement motion with an RMSE of 0.43 <inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula>.
Millimeter-wave radar interferometry is superior in detecting small displacement motions owing to its short wavelength. However, it is subject to phase ambiguity as the target displacement may often ...exceed a quarter wavelength. In this article, a modified differentiate and cross-multiply (MDACM) technique is proposed to tackle the phase ambiguity issue for accurate reconstruction of the phase history in millimeter-wave interferometry. In addition, to resolve the imperfections of the interferometric radar system, an MDACM-based integral phase reconstruction approach is presented, which seamlessly integrates alternating current (ac)-coupling-induced distortion correction, <inline-formula> <tex-math notation="LaTeX">I/Q </tex-math></inline-formula> mismatch correction, and direct current (dc) offsets' calibration. Without causing any phase ambiguity, the proposed technique acts as a black box to take in the raw <inline-formula> <tex-math notation="LaTeX">I/Q </tex-math></inline-formula> signals and correct all the hardware imperfections, and it outputs the desired displacement motions with micrometer accuracy. The simulation results show that the proposed technique can not only linearly recover the displacement motions across a wide range in different noise conditions without any phase ambiguity but also improve the stability by 11 times under ac-coupling-induced distortion. With a custom-designed 120-GHz interferometric radar sensor, experiments were carried out to validate various scenarios including mechanical vibrations and gesture sensing. The experimental results show that the proposed technique can accurately track not only deep subwavelength motion of only <inline-formula> <tex-math notation="LaTeX">1~\mu \text{m} </tex-math></inline-formula> but also multiwavelength displacement of >40 times of the wavelength at 120 GHz.
Cardiogram is one of the most important factors for health assessment. As a new expression of cardiograms, the Doppler cardiograms (DCGs) detected remotely via Doppler radar sensor (DRS) provide rich ...details of the heart motion. However, the existing techniques for measurement of DCG requires that the subject holds his/her breath to avoid the disturbance caused by respiration. To realize the accurate detection of DCGs in the presence of respiration, a high-linearity <inline-formula> <tex-math notation="LaTeX">K </tex-math></inline-formula>-band dc-coupled continuous-wave (CW) DRS with digital dc-tuning function was custom-designed and a novel parameterized respiratory filter (PRF) algorithm was proposed to precisely remove the respiratory signal. Both simulation and experimental results show that the proposed PRF algorithm has better DCG extraction performance than the conventional methods. Furthermore, the experimental results in normal and clinical environments show that the grained differential DCG (D-DCG) has promising potential in professional heart rate variability (HRV) analysis and heart diseases diagnosis, which means the proposed DCGs detection has the potential to be a convenient, comfortable, and reliable way for daily and clinical heart health assessment.
Due to the noncontact and low-cost features of Doppler radar sensors, it has been adopted to detect physiological motion signals in variety applications. This paper introduces two portable Doppler ...radar sensor devices named as "iMotion radar" and "iMotion2 radar". The iMotion radar is a 2.4-GHz AC-coupled direct-conversion continuous-wave Doppler radar. The iMotion2 radar is designed with the same structure except this version adopts DC coupling method in order to sense motions at very low frequency without frequency-dependence distortions. An additional circuit is designed for iMotion2 to eliminate large DC offset. Both of the two radars have been used in different applications. The experimental results have demonstrated good reliability and flexibility. The details in hardware design are given in this paper and two applications, which are achieved by those radar devices, are reviewed.
