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As an essential climate variable, soil moisture (SM) exerts an indispensable influence on numerous disciplines. However, various degrees of data gaps exist in current microwave SM products. Therefore, this article proposed a spatiotemporal attention-based residual deep network (STARN) to reconstruct gaps of the daily SM data from the Climate Change Initiative program of the European Space Agency (ESA CCI) over the Qinghai–Tibet Plateau (QTP) during unfrozen seasons (May to September) from 2001 to 2021. The developed model is an end-to-end residual network embedded with three attention modules to comprehensively consider the potential relationship between SM and surface variables. Evaluation results revealed that the proposed model could well reconstruct SM gaps with an overall median R and unbiased RMSE (ubRMSE) values of 0.52 and 0.054 m3/m3, while the overall median R and ubRMSE values for the ESA CCI SM were 0.41 and 0.058 m3/m3. Besides, comparison with five baseline methods (e.g., the artificial neural network, convolutional neural network, extreme gradient boosting, long-short term memory, and DCT-PLS model) indicated that the STARN model had certain advantages over the five baseline models with higher correlation and more reasonable distribution patterns. The R/ubRMSE values for the five models were 0.38/0.057, 0.34/0.058, 0.40/0.058, 0.41/0.056, and 0.41/0.058, respectively. The pretraining using the ERA5-Land SM data could further improve the accuracy of generated seamless SM data since the ERA5-Land and ESA CCI SM complemented each other to a certain extent on the QTP. In summary, by leveraging the spatiotemporal information and attention modules, the STARN model showed great potentials in SM gap filling.

In this letter, an all-metallized wideband dual circularly polarized antenna with endfire radiation is proposed for fifth-generation (5G) millimeter-wave applications. By introducing two rectangular notches on the side walls of open-ended waveguide, the vertical components are increased and close to the horizontal components in the broadband range so that the axial ratio (AR) bandwidth is enhanced. The simulated results show that the proposed antenna excited by wave port has 63.9% operation bandwidth (22.7–44.0 GHz), where reflection coefficients less than −10 dB, isolations greater than 20 dB, and AR less than 3 dB are achieved. To verify the design, the proposed antenna excited by coaxial connectors is fabricated and measured. Based on the measurement results, the reflection coefficients less than −10 dB, isolations greater than 20 dB, and AR less than 3 dB are achieved from 23.0–40.0 GHz, the endfire gain varies from 5.1 to 8.5 dBic at the frequencies mentioned above. [ABSTRACT FROM AUTHOR]

BGP-Multipath (BGP-M) is a multipath routing technique for load balancing. Distinct from other techniques deployed at a router inside an Autonomous System (AS), BGP-M is deployed at a border router that has installed multiple inter-domain border links to a neighbor AS. It uses the equal-cost multi-path (ECMP) function of a border router to share traffic to a destination prefix on different border links. Despite recent research interests in multipath routing, there is little study on BGP-M. Here we provide the first measurement and a comprehensive analysis of BGP-M routing in the Internet. We extracted information on BGP-M from query data collected from Looking Glass (LG) servers. We revealed that BGP-M has already been extensively deployed and used in the Internet. A particular example is Hurricane Electric (AS6939), a Tier-1 network operator, which has implemented >1,000 cases of BGP-M at 69 of its border routers to prefixes in 611 of its neighbor ASes, including many hyper-giant ASes and large content providers, on both IPv4 and IPv6 Internet. We examined the distribution and operation of BGP-M. We also ran traceroute using RIPE Atlas to infer the routing paths, the schemes of traffic allocation, and the delay on border links. This study provided the state-of-the-art knowledge on BGP-M with novel insights into the unique features and the distinct advantages of BGP-M as an effective and readily available technique for load balancing. [ABSTRACT FROM AUTHOR]

This article proposes a synthesis method of orthogonal beamforming networks (BFNs) with arbitrary ports. The proposed method is based on matrix decomposition theory and breakthrough the synthesized BFN number to arbitrary. It has been theoretically demonstrated that the BFN with cascading 180° hybrid couplers can synthesize shaped beams. Therefore, a BFN synthesis method that combines the QR decomposition theory and the optimization algorithm is introduced. With the help of an optimization program, a specific power ratio of each 180° hybrid coupler in the BFN is determined. The proposed synthesis method is verified by experiments with an orthogonal $6\times2$ BFN with flat-topped radiation patterns. Through optimization, five 180° hybrid couplers with different power ratios synthesize the proposed BFN. Results show that two flat-topped beams with a beamwidth of (32° ± 0.3°), gain ripples less than 2.5 dB, and a sidelobe level less than 12 dB are achieved. The proposed method has the advantages of high accuracy and efficiency and a simple structure, which makes it convenient for multi-beam antenna arrays in multiple-input–multiple-output (MIMO) systems. [ABSTRACT FROM AUTHOR]

In this letter, a wideband high-efficiency 1-bit 16 × 16 reconfigurable reflectarray antenna (RRA) is proposed. First, a wideband and low loss 1-bit RRA element is designed. It consists of double-layer patches printed on two dielectric substrates, respectively, forming a multiresonant behavior to expand the bandwidth.Due to the relatively thin thickness of the double-layer dielectric substrate (0.05 λ0), the element has low reflection loss. Therefore, the high efficiency and wide bandwidth performances can be obtained simultaneously. The phase difference between the two states of the RRA element is stable within 180 ± 20° in the frequency range of 12.9–16.5 GHz. Based on the broadband RRA element, a 16 × 16 RRA was fabricated and measured. Tested results show that the proposed RRA achieves 22.5% of 1 dB gain bandwidth and 25% of maximum aperture efficiency. [ABSTRACT FROM AUTHOR]

A broadband wide-angle scanning array antenn a with suppressed mutual coupling for fifth-generation (5G) sub-6G mobile communication applications is presented in this letter. The metal columns are positioned below the edge of the dipole, leading to the improved the impedance matching characteristics, the suppressed mutual coupling and a wider scanning angle. A 1×8 prototype of the suggested design has been manufactured and tested to ensure its usefulness. The overall dimension is 2.33 λ0×0.28 λ0×0.24 λ0 (λ0 is the free-space wavelength at 2.5 GHz). The measured and simulated results are quite consistent. The main lobe achieves a scanning range of ±60° at 2.5–4.5 GHz (57.1%) and yields a scanning range of ±75° at 3–4 GHz (28.6%) with a gain loss of less than 2.5 dB. The sidelobe levels are mostly less than or equal to −7.9 dB and the isolation between the antenna elements can yield a maximal additional 14.7 dB enhancement. [ABSTRACT FROM AUTHOR]

This communication presents the design of a wideband circularly polarized (CP) antenna array based on sequential rotation (SR) technique that is excited by a substrate integrated coaxial line (SICL) with mature and stable processing technology for millimeter-wave (mm-wave) applications. Initially, the influence of the amplitude and phase errors of the feeding network on the axial ratio of the CP array is analyzed, and the detailed design scheme of the wideband CP array based on SR technology is summarized, which can be used to design SR CP array with wide bandwidth and high polarization purity. Then, an SICL-fed $4 \times 4$ CP array working in the mm-wave band that is composed of two substrate layers and a bonding film layer is designed. The radiation element is processed with a larger chamfering, which can realize elliptically polarized radiation in a broadband range, and the impedance bandwidth is significantly expanded relative to the working state of linearly polarized and CP, which has a significant impact on the final array working bandwidth enhancement. The feeding network and radiation elements are directly connected in the same plane. Finally, the proposed antenna is processed and measured to verify the theory and design scheme in this communication. Over the frequency range of 25.0–34.0 GHz, the measured 1.5 dB axial ratio bandwidth of the fabricated prototype is 30.5%, and the return losses are less than −10 dB. The maximum measured peak gain is 16.5 dBi. [ABSTRACT FROM AUTHOR]

This article presents a novel miniaturized almost all-angle-insensitive strong coupled frequency-selective surface (SC-FSS) with all-polarization-insensitive multiband by introducing the different interlayer coupling patches. Two templates of a single passband and a dual passband with unit cell less than $0.03\lambda $ are adopted to bring in two stopbands on both ends of each passband. Furthermore, the corresponding equivalent circuit models are developed to explain the physical mechanism and formulate relevant design equations. Finally, a prototype of the proposed dual-passband structure is fabricated and measured to verify the results of full-wave simulation and theoretical analysis. The experiment results show that there are a lower passband working at 2 GHz and a higher passband at 5.8 GHz with a lower stopband at 4 GHz and a higher at 7.5 GHz at the ends of above passbands, respectively, which exhibits the stable performance against the variation of the incident angles (from 0° to 86°) for both TE and TM polarizations. The measurement results demonstrate that the proposed multiband SC-FSS is a good candidate for designing a high-performance antenna radome for solving electromagnetic interference (EMI) problems. [ABSTRACT FROM AUTHOR]

A substrate integrated waveguide (SIW) H-plane filtering horn antenna with embedded metallized via-hole arrays is proposed in this letter. The SIW H-plane filtering horn originates from a simple SIW H-plane horn with very narrow bandwidth and no frequency selectivity performance. To significantly increase bandwidth, two metal strips are printed on both sides of the substrate near the radiating aperture of the horn antenna. Critically, four rows of inductive metallized via holes are embedded into the flare region of the horn antenna, forming three coupled resonant cavities to achieve filtering function without any increase of the antenna dimension. The proposed SIW H-plane filtering horn antenna achieves good frequency selectivity, which satisfies the increasing demand of the miniaturization and integration of multifunctional devices. An optimized prototype is manufactured and measured to verify the design feasibility. The results show that the filtering performance is successfully realized with high level of integration. [ABSTRACT FROM AUTHOR]

In this communication, a novel frequency and polarization-reconfigurable antenna is designed based on simple dipole-type structure. It is composed by two symmetric bow-tie arms and four switching circuits. Four p-i-n diode switches are used to change the connection state of the bow-tie arms and other four patches. By switching the states of four p-i-n diodes, both the amplitude and phase of the surface currents at different frequencies can be controlled. It follows that an adjustable antenna in frequency and polarization can be devised. As a result, this antenna can realize different working modes. It can be mainly classified into six modes: two single broadband frequency linear polarization (LP) modes (Modes 1 and 2), two dual-broadband LP modes (Modes 3 and 4), and two dual-band circular polarization (CP) modes (Modes 5 and 6). In order to verify the accuracy of this design, this antenna is designed, fabricated, and tested. The measurement results agree very well with the simulation results. [ABSTRACT FROM AUTHOR]