Conical-beam antenna with four notch slots

Conical-beam antennas are widely used in satellite communication and radar systems. In this paper, a 4-element array consisting of four notch slots is proposed to generate conical-beam radiation. Simulated results are presented to demonstrate the good performance of its conical-beam radiation when the array elements are fed in phase with equal amplitude

Searching for <i>γ</i>-ray Emission from Binary Black-Hole Mergers Detected in LIGO/Virgo O3 Run

We conduct searches for γ-ray emission from the binary black-hole (BBH) mergers reported in the Gravitational-Wave Candidate Event Database (GraceDB). The γ-ray data are from the all-sky survey of the Large-Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope (Fermi), which allows searches for events of given time durations in large sky areas. The Two-Micron All-Sky Survey Photometric Redshift Catalog (2MPZ) is used for target selection, from which galaxy sources within the 90% credible areas and the distance ranges given by the gravitational-wave (GW) detections are determined. Excluding those BBH cases with large credible areas and/or dense fields (containing too many 2MPZ sources), searches for short transient events over the time duration of from −1 to 100 days of a trigger time for seven BBH mergers are conducted. We find two candidate short flaring events in the field of the GW event S200311bg and one in that of S190408an. However, the flaring events all have low significance (after considering the trial factor), and the third one appears off the position of the target galaxy. We discuss one of them from the first field that is detected in different short time-bin data and suggest that it is possibly a real flare arising from a radio galaxy. More such studies for the near-future GW detection run are planned, for which we will adjust our search strategy to be more effective and target flares of various time scales

Broadband circularly-polarised antenna consisting of four notch slot radiators

A broadband antenna consisting of four notch slots is proposed to generate circularly-polarised radiation. Wide bandwidth is achieved by using notch slots operating in the double-resonance range. A separate feeding network is designed to meet the requirement of sequential rotation excitation for the four slots maintaining a corresponding phase difference of 908 between adjacent slots. Simulated and measured results are presented to demonstrate the high directivity and wide bandwidth of the circularly-polarised antenna. The designed antenna exhibits a bandwidth from 4.9 to 6.1GHz for both |S11|≤ 210 dB and AR≤ 3 dB, which is 21% of the centre frequency of 5.5GHz. Peak gain at 5.5 GHz is 7.6 dBic along the zenith direction, with less than 1dB gain variation within the operating bandwidth

Function-reconfigurable water short backfire antenna

A novel short backfire antenna realized by replacing the metallic wall with water wall is described in this paper. Through controlling the water flow in different layers, the proposed short backfire antenna based on a cylindrical waveguide made of water can switch between two different functions. When the proposed antenna works in Function I, it is a short backfire antenna with pencil beam. When it operates in the other function, conical beam is achieved, and its beam angle can be changed by controlling the height of water cylinder and water wall. Measured results show that when working in Function I, the proposed water short backfire antenna has an impedance bandwidth (|S11| <; -10 dB) of 11.3% (3.6 GHz to 4.05 GHz). A maximum gain of 10.8 dBi is observed. While working in Function II, the beam angle of a conical radiation beam can be switched between 25° and 60°. The operating frequency of the antenna working in Function II covers a range of 5% (3.9 GHz to 4.1 GHz). Maximum gain of 6.8 dBi for 25° and 2.7 dBi for 60° is obtained. Due to its low cost, good radiation performances, transparent characteristic, and reconfigurability, this novel water antenna may be potentially useful in future communication applications.Published versio

Pattern-reconfigurable water horn antenna

A novel horn antenna is reported in this communication, which is realized by using water walls instead of traditional metallic walls. Due to its fluidity, water filling different channels can be readily controlled. Therefore, the proposed water horn antenna can operate in two states: H-plane horn state and leaky-wave state, resulting in different radiation patterns. The energy bounding effects of a water layer are initially studied for choosing the suitable thickness of the water walls. EHmn modes are excited and can propagate along the water waveguide. The E-field and H-field distributions of the EHmn modes are similar to the TE and TM modes excited inside a metallic rectangular waveguide. Propagation constants of the EHmn modes have been extracted from simulation results, and it is found that a leaky wave can be excited. Measured results show that the proposed water horn antenna has an impedance bandwidth (|S11| <−10 dB) from 2.5 to 5.2 GHz (70.1% fractional bandwidth) for the H-plane horn state and from 2.6 to 5.7 GHz (74.7% fractional bandwidth) for the leaky-wave state. The proposed antenna achieves a maximum gain of 11.8 dBi for the H-plane horn and 7.7 dBi for leaky-wave state. The proposed water horn antenna has the advantages of reconfigurability and transparency, which may be potentially useful in many wireless communication applications.This work was supported in part by the National Natural Science Foundation of China under Grant 61771242

UAV aided network association in space-air-ground communication networks

Unmanned aerial vehicles (UAVs) cooperating with satellites and base stations (BSs) constitute a space-air-ground three-tier heterogeneous network, which is beneficial in terms of both providing the seamless coverage as well as of improving the capacity for the users. However, cross-tier interference may be inevitable among these tightly embraced heterogeneous networks. In our paper, we propose a two-stage joint hovering altitude and power control solution for the resource allocation problem. Furthermore, Lagrange dual decomposition and concave-convex procedure (CCP) method are used to solve this problem. Finally, simulation results show the effectiveness of our proposed two-stage joint optimization algorithm in terms of UAV network's total throughput.</p

Dynamic Behavior Investigation of a Novel Epidemic Model Based on COVID-19 Risk Area Categorization

This study establishes a compartment model for the categorized COVID-19 risk area. In this model, the compartments represent administrative regions at different transmission risk levels instead of individuals in traditional epidemic models. The county-level regions are partitioned into High-risk (H), Medium-risk (M), and Low-risk (L) areas dynamically according to the current number of confirmed cases. These risk areas are communicable by the movement of individuals. An LMH model is established with ordinary differential equations (ODEs). The basic reproduction number R0 is derived for the transmission of risk areas to determine whether the pandemic is controlled. The stability of this LHM model is investigated by a Lyapunov function and Poincare&ndash;Bendixson theorem. We prove that the disease-free equilibrium (R0 &lt; 1) is globally asymptotically stable and the disease will die out. The endemic equilibrium (R0 &gt; 1) is locally and globally asymptotically stable, and the disease will become endemic. The numerical simulation and data analysis support the previous theoretical proofs. For the first time, the compartment model is applied to investigate the dynamics of the transmission of the COVID-19 risk area. This work should be of great value in the development of precision region-specific containment strategies

Dynamic Behavior Investigation of a Novel Epidemic Model Based on COVID-19 Risk Area Categorization

This study establishes a compartment model for the categorized COVID-19 risk area. In this model, the compartments represent administrative regions at different transmission risk levels instead of individuals in traditional epidemic models. The county-level regions are partitioned into High-risk (H), Medium-risk (M), and Low-risk (L) areas dynamically according to the current number of confirmed cases. These risk areas are communicable by the movement of individuals. An LMH model is established with ordinary differential equations (ODEs). The basic reproduction number R0 is derived for the transmission of risk areas to determine whether the pandemic is controlled. The stability of this LHM model is investigated by a Lyapunov function and Poincare–Bendixson theorem. We prove that the disease-free equilibrium (R0 R0 > 1) is locally and globally asymptotically stable, and the disease will become endemic. The numerical simulation and data analysis support the previous theoretical proofs. For the first time, the compartment model is applied to investigate the dynamics of the transmission of the COVID-19 risk area. This work should be of great value in the development of precision region-specific containment strategies