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A novel compact fan-shaped folded waveguide resonator (FSFWGR) is proposed in this article. The resonator can reduce the size by 87.5% compared with the waveguide cavity while retaining a high unloaded quality ( $Q_{{u}})$ value (>1500). Due to these advantages, a high-quality (-Q) fourth-order bandpass filter centered at 6.0 GHz with a 6.67% bandwidth is designed first. Novel slots cross-coupling is presented to produce a pair of transmission zeros (TZs) while avoiding support structures that traditional metal probes often used. Then compact deformed folded antenna is designed to integrate with the filter. Compared with published works where the last resonator of the reference filter often needs to be detuned, all parameters here do not need to change by introducing a metal probe between the feeding point of the filter and antenna. Therefore, the integrating process is more straightforward. The integrated filter/antenna achieves the same filtering function as the reference filter and a high gain of 6.7 dBi. For experimental demonstration, metal 3-D printing technology was used to fabricate models with only two pieces that significantly reduced the assembly loss. The final measured results agreed well with simulated ones.

Radio frequency fingerprint (RFF) identification distinguishes wireless transmitters by exploiting their hardware imperfection that is inherent in typical radio frequency (RF) front ends. This can reduce the risks for the identities of legitimate devices being copied, or forged, which can also occur in conventional software-based identification systems. This paper analyzes the feasibility of device identification exploiting the unique non-linear memory effect of the transmitter RF chains consisting of matched pulse shaping filters and non-linear power amplifiers (PAs). This unique feature can be extracted from the received distorted constellation diagrams (CDs) with the help of image recognition-based classification algorithms. In order to validate the performance of the proposed RFF approach, experiments are carried out in cabled and over the air (OTA) scenarios. In the cabled experiment, the average classification accuracy among systems of 8 PAs (4 PAs of the same model and the other 4 of different models) is around 92% at signal to noise ratio (SNR) of 10 dB. For the OTA line-of-sight (LOS) scenario, the average classification accuracy is 90% at SNR of 10 dB; for the non-line-of-sight (NLOS) scenario, the average classification accuracy is 79% at SNR of 12 dB.

In this paper, we study the named entity recognition (NER) problem under distant supervision. Due to the incompleteness of the external dictionaries and/or knowledge bases, such distantly annotated training data usually suffer from a high false negative rate. To this end, we formulate the Distantly Supervised NER (DS-NER) problem via Multi-class Positive and Unlabeled (MPU) learning and propose a theoretically and practically novel CONFidence-based MPU (Conf-MPU) approach. To handle the incomplete annotations, Conf-MPU consists of two steps. First, a confidence score is estimated for each token of being an entity token. Then, the proposed Conf-MPU risk estimation is applied to train a multi-class classifier for the NER task. Thorough experiments on two benchmark datasets labeled by various external knowledge demonstrate the superiority of the proposed Conf-MPU over existing DS-NER methods., Accepted in ACL 2022

The design and operation of a compact antenna array offering circularly polarized (CP) radiation for picosat and other small satellites for communication applications is presented. The proposed array combines folded-shorted patches (FSPs) and meandering for antenna miniaturization. Realization of CP is achieved by a compact and planar feed circuit consisting of a network of meander-shaped 90- and 180-degree hybrid couplers which can provide quadrature feeding of the FSP elements and can be integrated onto the backside of the antenna ground plane which is only 5 cm by 5 cm. Agreement in terms of the simulations and measurements is observed with realized gain values of more than 3 dBic at 1.065 GHz and with an antenna size of ${0.17\lambda 0}$ by ${0.17\lambda 0}$ .

The development of radio frequency fingerprint (RFF) identification technique aims to identify and classify wireless devices by exploiting their unique radio frequency (RF) features. This paper proposes a wireless device RFF identification scheme, which relies on the non-linear memory effect resulting from the concatenation of two matched root-raised cosine (RRC) filters with a non-linear power amplifier (PA) inserted in-between. This unique feature can be extracted from the distorted constellation diagrams, which is processed into density trace figure. Classification algorithm based on image recognition method is developed to exploit the non-linear memory effect from the density trace figure. Simulation setup is carefully designed, and the results validated the effectiveness of our proposed RFF feature classification approach. In the range of SNR 1 dB to 25 dB, the overall identification accuracy rate exceeds 99%.

A compact and flexible coplanar waveguide-fed (CPW) monopole antenna is presented for operation at four different wireless bands. The antenna design is based on a simple rectangular patch which is then integrated with multiple L-shaped slots to enable multiband operation at 1.22, 1.56, 2.45 and 3.42 GHz, offering a reflection coefficient of -10 dB at these frequencies. Modeling is performed using FEKO, a commercial software, based on two approaches: the method of moments (MoM) and characteristic mode analysis (CMA). Results show satisfactory agreement of the predicted resonant frequencies. In addition, radiation efficiency, realized gain, bandwidth and current distributions are discussed in the paper. Finally, a systematic investigation of the bending effects for the proposed wearable antenna is also presented.

A compact circularly polarized (CP) antenna array is presented. The array utilizes folded-shorted patches (FSPs) and printed circuit board (PCB) technology for antenna miniaturization. Both techniques enable a size decrease of the quarter-wavelength shorted-patch by a factor of 1/N, where N is number of the layers above the ground plane while maintaining a quarter-wavelength resonant length. This results in a reduction of the antenna length by half or more. The feature of CP is achieved by a compact and planar feeding circuit defined by a network of meandered 90 and 180-degree hybrid couplers which can provide quadrature feeding of the FSP elements and can be integrated onto the backside of the antenna ground plane which is only 9 cm × 9 cm. To fine tune the resonant frequency of the FSP antenna, we select different relative permittivity values for the substrate. Agreement in terms of the simulations and measurements is observed for the compact antenna (size of 0.129λ × 0.129λ × 0.014λ) with realized gain, radiation beam patterns and axial ratio values reported at UHF frequencies (430 MHz).

This paper presents the design of a circularly polarized (CP) meshed patch antenna fully integrated within a solar panel for operation on CubeSats and other microsatellites. The structure has been designed to ensure optimal antenna performance at $S$ -band as well as to minimize any shadowing effects that can reduce the received power at the solar cells. To generate CP, the antenna is driven by two orthogonal feed points, penetrating through a transparent borosilicate glass layer, as well as a silicon and PCB substrate. Simulated and measured performances, on both a preliminary FR4 design and a fully integrated prototype, demonstrate a good impedance bandwidth, satisfactorily axial ratio, as well as stable radiation patterns and minimum shadowing levels. The proposed antenna can be useful for communications between satellites as well as with the ground station, and since the structure is compact and completely integrated, the design can be an alternative approach to new-phased arrays on solar panels and other beam-steering systems.

The design and operation of a miniaturized antenna array offering circularly polarized (CP) radiation for CubeSats and other micro-satellites is presented. The proposed antenna array combines folded-shorted patches (FSPs) and meandering for antenna miniaturization. Both techniques enable a decrease of the quarter-wavelength shorted patch while maintaining a quarter-wavelength resonant length. Realization of CP is achieved by an ultra-compact and planar feed circuit consisting of a network of meander-shaped 90° and 180° hybrid couplers, providing quadrature feeding of the FSP elements and for integration onto the backside of the antenna ground plane whose physical dimension is only 9 cm × 9 cm. Good CP performances are observed for the developed UHF-band antenna for the CubeSat standard and with a size of only $0.135 \lambda \times 0.135 \lambda$ considering the 450 MHz design frequency.