The underlying mechanisms of multipactor between dielectric and metal and the discharge threshold of practical dielectric components have been investigated numerically and experimentally in this paper. The reduction in secondary electron yield (SEY) and the change in surface condition are achieved using the microstructure processing technology on both of ferrite dielectric and metal. Combined with the electromagnetic particle-in-cell method, the SEY model fit with the experimental data is utilized to simulate multipactor in three groups of ferrite circulators with different surface conditions. Simulation and experimental results demonstrate that the multipactor threshold of the circulator is increased by a factor of 2 through the SEY reduction on the ferrite and is increased by a factor of more than 8, from 380 W to more than 3400 W, through the SEY reduction on both of the ferrite and the metal. Different multipactor discharge mechanisms, including two-side multipactor with positive charge accumulation, singe-side multipactor with negative charge accumulation, and multipactor suppression effect, exist in circulators with the same physical structure and different surface conditions.

This article presents a waveguide with a pair of E -plane bends and two waveguide bandpass filters (BPFs) which operate in WR-3.4 band (220–330 GHz). These devices are fabricated by a micro metal additive manufacturing (M-MAM) technology on copper in one piece. Both filters are fifth order and operate at a center frequency of 280 GHz with a bandwidth of 8 GHz. Cylindrical resonators are employed for filter design. The standard feed waveguides are designed in bend structures, facilitating the measurements. The M-MAM technology is a layer-by-layer additive manufacturing process constructing the waveguide devices in five layers. Since the layout of the devices has a strong impact on the electrostatic field distributions and hence the electroforming quality, both full-wave electromagnetic (EM) simulations and electrostatic analysis are simultaneously considered in the device design. It eases the subsequent electroforming and polishing processes, effectively improving the performance of the devices. The insertion losses and return losses of the measured filters are lower than 1.65 dB and better than 15 dB. The center frequency shifts are less than 0.3%. The excellent results attribute to the delicate co-design method between EM and electrostatic analyses encountered both in the filter design and in the additive manufacturing process.

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.

With the development of industrial civilization, advanced manufacturing technology has attracted widespread concern, including in the aerospace industry. In this paper, we report the applications of ultra-thin atomic layer deposition nanofilm in the advanced aerospace manufacturing industry, including aluminum anti-oxidation and secondary electron suppression, which are critical in high-power and miniaturization development. The compact and uniform aluminum oxide film, which is formed by thermal atomic layer deposition (ALD), can prevent the deep surface oxidation of aluminum during storage, avoiding the waste of material and energy in repetitive production. The total secondary electron yield of the C/TiN component nanofilm, deposited through plasma-enhanced atomic layer deposition, decreases 25% compared with an uncoated surface. The suppression of secondary electron emission is of great importance in solving the multipactor for high-power microwave components in space. Moreover, the controllable, ultra-thin uniform composite nanofilm can be deposited directly on the complex surface of devices without any transfer process, which is critical for many different applications. The ALD nanofilm shows potential for promoting system performance and resource consumption in the advanced aerospace manufacturing industry.

This paper presents a D-band waveguide diplexer fabricated using micro metal additive manufacturing (M-MAM) technology. The diplexer features two sixth-order filters with passbands of 130-134 GHz and 141-148.5 GHz, respectively, for a crucial RF application band. Cylindrical resonators were employed in the filter design, and a 9-layer process was developed specifically for this frequency band, allowing the diplexer to be manufactured as a single piece. The process was optimized to minimize photo-resist deformation during repeated thermal cycles, so a larger waveguide can be fabricated. To ensure accurate measurements, a fixture equipped with a straight-through calibration channel was also designed and manufactured. The measured insertion losses and return losses of both channels are less than 2 dB and greater than 15 dB, respectively, and the center frequency shifts are negligible at less than 0.15%. The excellent correlation between simulations and measurements is a result of the carefully designed process and its high level of accuracy.