In this communication, 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 (CI) 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 λ0). The achieved decoupled bandwidths (BWs) are up to 17.6% and 22.2% for the aperture-coupled and probe-fed schemes, respectively. In addition, the proposed method has been extended to the decoupling of multielement antenna arrays, demonstrating its potential for large-scale wideband massive multiple-input and multiple-out (MIMO) applications. © 1963-2012 IEEE.

This article presents a novel 5.8-GHz ISM-band dual-circularly polarized (CP) simultaneous transmit and receive (STAR) common-aperture antenna array (CAAA) for integrated sensing and communication (ISAC) in Internet of Things (IoT). A new near-field cancellation technique based on differential feeding and geometrical symmetry is proposed for dual-CP to realize high TX/RX isolation. In addition, a high-impedance surface is introduced to further improve the TX/RX isolation. Furthermore, the parasitic patches are added to enhance the gain and isolation bandwidth (BW). The simulation results demonstrate that the proposed CAAA possesses the merits of high isolation (up to 67 dB), wide isolation BW (better than 40 dB for 240 MHz BW), high gains (up to 10/10.5 dB for right-hand CP (RHCP)/left-hand CP (LHCP)), wide 1-dB gain BWs (better than 230/350 MHz BW for RHCP/LHCP), and low-axial ratios (lower than 1.4 dB). The designed CAAAs are fully characterized and the experimental results meet the simulation very well. For the first time, systematic validations for both wireless communication and radar sensing have been thoroughly carried out by integrating the proposed CAAA in the custom-designed full-duplex radio system. The experimental results not only prove the validity of the design methodology but also the feasibility of employing the proposed CAAA for ISAC, which indicates potential applications in IoT era.

The ranging accuracy and range resolution in linear-frequency-modulated continuous-wave (LFMCW) radars are vulnerable to the nonlinearity of the transmitted frequency ramp. The frequency ramp nonlinearity (FRN) leads to the degradation of accuracy in range estimation and deteriorates the range resolution in LFMCW radars, which becomes even worse as the target range increases. The uncertainty of the type of FRN makes the problem more complicated. This article proposes a new range-dependent resolution model and a new range-dependent accuracy model based on the theoretical analysis and experimental evaluations, which characterizes the impact of different types of FRN on the range resolution and accuracy in LFMCW radars. The proposed models have established the quantitative relationship between the FRN, the target distance, and the range accuracy and resolution. A nonlinearity index is utilized in the analysis to quantify the extent of FRN. Moreover, a novel design methodology is also proposed, which may guide the design of LFMCW radars under the influence of FRN. Four typical types of FRN that are reasonable in practical LFMCW radars are taken into consideration in both simulations and experiments to validate the proposed theory and methodology.

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 K-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.

A novel 4-D gesture sensing technique using reconfigurable virtual array method with a 60-GHz frequency-modulated continuous wave (FMCW) radar is presented. The 4-D sensing includes the 3-D spatial positioning and the 1-D motion tracking, which combines detection in both spatial and temporal domains. The proposed technique can be used for gesture sensing for both macro gestures such as handwriting letters and numbers, hand drawing different patterns in space and micro gestures such as the fingers' actions of virtual slider, finger tap, and finger wave. Moreover, this work presents a method to reconfigure the working modes of different transmitting and receiving channels in the multiple input and multiple output (MIMO) architecture, which effectively increases the sensing range of the radar sensor and the signal-to-noise ratio (SNR) of the beat signal. For various gestures at different distances or in different environments, the proposed technique can adaptively achieve the best detection by reconstructing the virtual array of the MIMO radar. A series of experiments are carried out in both microwave anechoic chamber and office environments to validate the proposed technique. The experimental results show that the proposed technique performs well in sensing a variety of both macro gestures and millimeter-level micro gestures. Compared with the conventional MIMO method, the proposed technique increases the sensing range by 3.5 times, and the SNR is also greatly improved by 12 dB when the radar performs gesture sensing at the distance of 0.65 m.

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.