Capable of remote presentations of human heart activities, the Doppler cardiogram (DCG) can be detected by an agile Doppler radar sensor. However, as a recently developed technology, its performance needs sustained improvements for the future practical applications. In this work, a continuous-wave, ${V}$ -band Doppler radar sensor was implemented to improve the discrimination of the receiver, for detecting micrometer-level details of heartbeat motions conducted to the chest skin. Besides, new algorithms were derived to achieve high linearity, to demodulate the Doppler phases and retrieve the fine details of DCG waveforms. Experimental measurements to different subjects showed significantly enhanced robustness and accuracy. The obtained results imply a promising potential of DCGs in wide application scenarios such as medical wisdom and personal healthcare.

Microwave frequency-hopping signal generation is one of the backbone components in modern wireless communication system. In this paper, we propose a novel photoelectric integrated approach to implement broadband microwave frequency-hopping signal generation. The coherent dual optical combs are constituted by two Mach Zehnder modulators (MZMs) and one acousto-optic frequency modulator (AOM). By using dense wavelength division multiplexing (DWDM) and single-sideband modulation with carrier suppression, the proposed method extends the input signal's frequency hopping bandwidth by six times. Due to the photoelectric hybrid structure, the proposed method can achieve precise control for using electronic technology while also providing the advantages of high bandwidth and reconfigurability through photonics. In the experiment, the frequencies of generated signals can hop ranging from 0 to 6GHz. Meanwhile, the frequency hopping signals can maintain a well signal quality with the EVM lower than 6.4%.

In the past decades, continuous Doppler radar sensor-based bio-signal detections have attracted many research interests. A typical example is the Doppler heartbeat detection. While significant progresses have been achieved, reliable, time-domain accurate demodulation of bio-signals in the presence of unavoidable DC offsets remains a technical challenge. Aiming to overcome this difficulty, we propose in this paper a novel demodulation algorithm that does not need to trace and eliminate dynamic DC offsets based on approximating segmented arcs in a quadrature constellation of sampling data to directional chords. Assisted by the principal component analysis, such chords and their directions can be deterministically determined. Simulations and experimental validations showed fully recovery of micron-level pendulum movements and strongly noised human heartbeats, verifying the effectiveness and accuracy of the proposed approach.

This letter presents a low-cost third-harmonic mixer suitable for W-band retrodirective systems. Measured results show that when fixing the local oscillator (LO) frequency at 35 GHz, the conversion loss (CL) below 11 dB is achieved over the radio frequency (RF) range of 100–110 GHz with intermediate frequency (IF) from dc to 5 GHz, while for the RF range of 108 GHz, the minimum CL of 6.8 dB is obtained. Therefore, the presented mixer exhibits an excellent performance with low CL in comparison with that of a normal subharmonic mixer (SHM). The isolations of RF/LO and RF/IF are improved to the level of 35 and 38 dB, respectively. The simulated and measured isolations of LO/RF are 41 and 37 dB, respectively. This mixer has properties of low LO frequencies, high isolations, and low CL; therefore, it provides a high-performance and low-cost alternative solution for the applications of retrodirective systems.

Future communications will provide higher transmission rates and higher operating frequencies. In addition, agile beam tracking will be an inevitable trend

Microwave imaging under the illumination of randomized fields has demonstrated promising potential. Recent results showed that based on a phase-reconfigurable frequency-selective surface (PFSS), a cost-effective 24-GHz imager can be implemented, showing a wavelength-scale resolution. In this work, we further improve this imager by realizing duplexed random phase modulations. Numerical and experimental results showed that based on the same PFSS, the proposed duplex imager can significantly increase the number of available independent measurements (AIMs) and the sensing capacity. As the result, the error of the reconstructed image can be reduced by 49%, and the imaging resolution reaches 6.25 mm, that is, a half wavelength at 24 GHz. The aperture of the proposed duplex imager can be conveniently extended, exhibiting a promising potential in low-cost security scanning applications, especially for large objects such as human bodies.