Search

In this letter, a design of broadband microstrip three‐way directional coupler (TWDC) is presented. The broadband performance of the microstrip TWDC is realized by the method of cascading multi‐section. The broadband TWDC is designed to achieve equal power division and −120°, 0°, and +120° phase differences between output signals. To verify the broadband design, a prototype of three‐section microstrip TWDC operating at C‐band is designed, fabricated and measured. The measured results show that the power division error of the designed broadband TWDC is less than ±0.7 dB and phase error is less than ±12° at a relative bandwidth of 16%. To verify its performance in multibeam application, the designed TWDC is used as a beamforming network for multibeam antenna array to generate three orthogonal beams. [ABSTRACT FROM AUTHOR]

This letter presents a wideband high gain substrate integrated waveguide horn antenna (SIWHA) loaded with half Maxwell fish‐eye (HMFE) fabricated by 3‐D‐Printing. The impedance bandwidth of the SIWHA is narrow, mainly caused by the discontinuity between the substrate with the air. By introducing the HMFE and a match layer between the SIWHA with HMFE, the impedance continuity can be realized, which can not only improve the impedance bandwidth but also enhance the antenna gain. Experimental results show that the proposed antenna can achieve more than 6 dBi gain and 60.9% relative impedance bandwidth with reflection coefficients lower than −10 dB. [ABSTRACT FROM AUTHOR]

A fast and efficient method is proposed in this letter to characterize the dielectric permittivity of thin‐film materials. The measuring system is based on a TE103 rectangular split‐cavity resonator operating at around 10 GHz, which has the advantage of providing nondestructive measurements while maintaining a high level of accuracy. The thin‐film materials under test can be directly inserted in the split without being processed in a specific shape. Different dielectric materials are tested using this method. And the theoretical derivations and experimental measurements have been performed to confirm the validity and effectiveness of this approach. [ABSTRACT FROM AUTHOR]

A design of millimeter wave (mm‐wave) dual‐polarized multibeam antenna array (MAA) with a boresight beam is presented. In order to generate a boresight beam, a 5 × 6 Butler matrix based on three‐way directional couplers is designed as the beamforming network, which achieves equal power division and −60°, +120°, 0°, −120°, +60° progressive phase differences among the output ports when the five input ports are excited, respectively. By four‐layer design, the two 5 × 6 BMs for horizontal polarization (HP) and vertical polarization (VP) are constructed. The patch is used as radiator element, and the HP and VP wave are excited by aperture coupling and microstrip feed, respectively. A prototype is fabricated and measured to verify the design. The measured results show that the designed mm‐wave dual‐polarized MAA can generate five radiation beams including a boresight beam and the five beams with HP and VP cover the range of ±50° at 28 GHz. In addition, the designed mm‐wave dual‐polarized MAA can be a potential option for mm‐wave multibeam application. [ABSTRACT FROM AUTHOR]

In this letter, two miniature spoof surface plasmon polaritons (SSPPs) unit structures are proposed. A trident‐shaped groove and a Jerusalem cross‐shaped groove are respectively designed to increase the equivalent depth of the groove so as to realize the reduction of the line‐width. With smaller size, the proposed units have the equivalent dispersion of classical unit. To validate the properties of the proposed units, SSPPs transmission lines (TLs) are designed. Compared with the classical rectangular grooved SSPPs TL, the proposed unit with trident‐shaped groove and Jerusalem cross‐shaped groove can achieve the similar transmission performance with a line‐width reduction of 44.4% and 19.1%, respectively. The measured results of TLs agree well with the simulated ones, which validates the designs. Moreover, the proposed unit structures confine field more effectively. The proposed structures are attractive and useful for the miniaturization of SSPPs devices. [ABSTRACT FROM AUTHOR]

Regarding the three expansion modes of hydraulic fractures at the interface of a coal measure composite reservoir (arrested, deflection, and penetration), based on the coupling theory of fluid flow and solid elastic deformation, a criterion that considers the influences of the injection parameters (fracturing fluid injection rate and viscosity) is established to predict the propagation path of hydraulic fractures at the interface of a composite reservoir. The criterion judges the propagation behavior of the fractures by comparing the water pressure in the wellbore and the critical seam pressure of the penetration and deflection. The controlled variable method is used to analyze the influences of the various factors on the propagation behavior of hydraulic fractures at the interface between layers. The results show that the differences in in situ stress, the interface cohesion, and the included angle mainly affect the critical seam pressure of the fracture deflection. The differences in elastic modulus, fluid injection rate, and fracturing fluid viscosity directly affect the water pressure in the wellbore. The difference in the fracture toughness mainly affects the crack propagation path by affecting the critical seam pressure of the deflection. The smaller the difference in the in situ stress is, the more likely it is that the hydraulic fractures will penetrate the layer. Larger differences in the fracture toughness between layers, interfacial cohesion, fluid injection rate, and fracturing fluid viscosity are more conducive to the hydraulic fractures penetrating the layer. When the angle between the hydraulic fractures and the interface is 25–55°, the hydraulic fracture is more likely to expand along the interface. This criterion takes into account the influences of the injection parameters and is of great significance to gaining a better understanding of the propagation behavior of hydraulic fractures at an interlayer interface. [ABSTRACT FROM AUTHOR]

This letter presents a wideband three-dimensional (3-D)-printed circularly polarized (CP) ultrathin dielectric slab waveguide (DSW) Luneburg lens (LL) with multibeam application in X-band. The characteristic that DSW supports TE0 and TM0 waves to pass through with different phase constants is used to generate 90° phase difference to compose CP wave for the proposed structure. To prove the point, the prototype antenna is fabricated by 3-D printing and measured. The results show that the proposed LL supports multibeam application with 11 beams covering ±60° range in azimuth plane, and the 3 dB axial ratio bandwidth for multibeam antenna is 23.5% with reflection coefficient lower than −10 dB and gain higher than 13.7 dBi. The measured results show good coincidence with simulated ones. [ABSTRACT FROM AUTHOR]

Luneburg lens (LL) and Eaton lens (EL) are well known as optical and microwave components. This letter proposes a bifunctional Luneburg-Eaton lens (LEL) fabricated by three-dimensional (3-D)-printed anisotropic medium. The spherical LEL is designed as a LL for incident vertical polarization and as an EL for incident horizontal polarization through the use of anisotropic dielectric. In order to realize a good continuous refractive index, the proposed lens structure is divided into many cells, and the equivalent permittivity of each unit is calculated by using the equivalent media theory. The prototype of LEL is designed and excited by X-band waveguide WR-90, and the ideal results are achieved. The gain of the antenna is from 15.7 to 16.4 dBi in X-band with the LEL functioning as a LL, and the waveguide can have a beam deflection of set angle with the LEL functioning as an EL. [ABSTRACT FROM AUTHOR]

This letter presents a simple method to design the wideband circularly polarized spherical multibeam Luneburg lens (LL) antenna by using three-dimensional (3-D)-printing. The conventional 3-D-printed spherical LL is divided into many cells and each cell is filled by the unit cell with different filling ratios, which breaks the circular symmetry of the LL. The proposed method divides the LL into many layers, and the profile surface equation of each layer is calculated by the ordinary least square method to keep the rotation symmetry of the LL. Then, according to the proposed circularly polarized implement method, the transformation of linear polarization to circular polarization can be realized by selecting a proper radius of LL. The simulated and measured results show that the axial ratios of the proposed multibeam LL antenna are less than 3 dB with good impedance performance and more than 13.8 dBi gain in a relative bandwidth of 31.6%, which demonstrates the validity and simplicity of the presented method. [ABSTRACT FROM AUTHOR]

A design of planar dual‐polarized differentially fed multibeam patch antenna array (DFMPAA) is presented in this article. The dual‐polarized DFMPAA is composed of two circular 4 × 4 butler matrixs (BMs) and a 1 × 4 dual‐polarized patch antenna array. The two BMs are designed in the top and bottom layer as the feeding network of horizontal polarization (HP) and vertical polarization (VP), respectively. The patch is designed as the radiation element of the dual‐polarized DFMPAA, which is fed by the slot and aperture coupling to generate the HP and VP wave, respectively. To achieve high cross‐polarization discrimination (XPD), the antenna element is fed differentially. A prototype working at 5.5 GHz is fabricated and measured in order to validate the performance of the proposed dual‐polarized DFMPAA. The dimension of the dual‐polarized DFMPAA is 3.8 λ0 × 1.7 λ0. Measured results show that when the beam scan to the maximal pointing angle, the XPD of the dual‐polarized DFMPAA in HP and VP are higher than 27 and 29 dB, respectively. Additionally, the beams of the dual‐polarized DFMPAA can cover the range of ±42° in horizontal plane. [ABSTRACT FROM AUTHOR]

In this letter, a design of multibeam antenna (MBA) with two-dimensional (2-D) beam steerable capability is proposed. The proposed MBA is composed of a circular 4 × 4 butler matrix (BM) and a 2 × 4 patch antenna array. And the 2 × 4 patch antenna array consists of four two-element subarrays uniformly arranged along the E-plane. By introducing the switching diodes in the subarray and controlling the switching diodes on and off, elements of the subarray are excited through the paths with different lengths, and the beam of the subarray is steered subsequently in the H-plane. The circular 4 × 4 BM is designed as the beamforming network to excite the four subarrays uniformly arranged along the E-plane and steer the beam in the E-plane. The proposed MBA can generate 12 beams by selecting the excitation port and controlling the on–off state of the switching diodes. To validate the performance of the proposed MBA, a prototype is fabricated and measured. By design, the dimension of the designed MBA has reduced to 2.9 λ0 × 1.3 λ0. The designed MBA operates at 5.7 GHz, and the results show that the beams of the MBA can cover the range of ±36° in the E-plane and ±22° in the H-plane, respectively. [ABSTRACT FROM AUTHOR]

In this article, a broadband dual circularly polarized (CP) antenna with simple structure and high gain is designed. A metal ridge septum with the shape of the cascade of a rectangle and a triangle is embedded into the square waveguide to excite CP wave, which is presented through analysis and simulation. By feeding the antenna at the two positions with respect to the symmetrical position of the septum, it can form the right‐handed circularly polarized (RHCP) and left‐handed circularly polarized (LHCP) wave, respectively. To verify the design, a prototype of the antenna is fabricated and measured. The measured and simulated results coincide with each other. According to the simulation and measurement, the designed antenna can work well within a relative bandwidth of 64% from 8.5 to 16.5 GHz. The proposed dual CP antenna has the simple configuration and good performance, and it can be a good candidate antenna for the broadband communication system. [ABSTRACT FROM AUTHOR]

This letter presents a broadband 3-D-printed circularly polarized (CP) spherical Luneburg lens (LL) with the linearly polarized feed antenna for the X-band. In order to implement spatially continuous varying effective refractive index (RI), the proposed LL is divided to many unit cells and their effective RI is simulated and calculated by effective medium theory. Since the effective RI of unit cells is anisotropic for two orthogonal linearly polarized (LP) waves, the proposed LL is an LP to CP polarizer realized by properly selecting the radius of the LL. The whole structure is fabricated by low cost 3-D-printing (3DP) technic, which is fed by an LP antenna source rotated to a certain angle with respect to the LL around the normal. The measured results indicate that the voltage standing wave ratio (VSWR), axial ratio, and gain enhancement are lower than 2, less than 2.8 dB, and more than 10 dB at X-band, respectively. The results of measurement agree well with the simulation. [ABSTRACT FROM AUTHOR]

In this study, we determined the first complete mitochondrial genome sequence of Coscinasterias acutispina Stimpson, 1862. The mitogenome was 16,186 bp in length and contained 13 protein-coding genes, two ribosomal RNA genes, and 22 transfer RNA genes. The gene order and direction were identical to those of other asteroid starfish species. Phylogenetic analysis showed that C. acutispina was located at the basal position of Forcipulatida, belonging to the genus Coscinasterias within the family of Asteriidae. [ABSTRACT FROM AUTHOR]

This letter presents a broadband active Van Atta array system at $X$ -band, which is used for monostatic radar cross section (RCS) modulation and enhancement. The active system mainly consists of two uniform linear arrays (ULAs) and an active four-channel radio frequency (RF) amplifying circuit. By introducing the electrically modulated attenuator (EMA) into the active system, the transmission gain of the proposed four-channel RF amplifying circuit is controlled by a voltage signal from a control circuit and the backscattering field of the system can be sequentially modulated. The system’s performance of RCS modulation and retrodirectivity are validated through measurement over a relative bandwidth of 40% centered at 10 GHz. The modulation range of monostatic RCS is generally more than 20 dB at the $X$ -band. Its 3-dB retrodirective range and maximum equivalent RCS are 70°–120° and 1.4–3.9 dBsm varying from 8 to 12 GHz, respectively. [ABSTRACT FROM AUTHOR]

The starfish Asterias amurensis is a marine pest native to the northwestern Pacific and has successfully invaded southern Australia. Asterias amurensis have caused substantial environmental and economic impacts in both native and non-native regions. However, little information is available about the genetic features of its native populations, especially for those in North China. Here we sequenced the complete mitochondrial genomes of five individuals from different locations in China and compared their characteristics with three mitogenomes available from Japan. Multiple analyses and comparisons revealed little difference in the gene composition, gene order, codon usage, and nucleotide content among the eight mitogenomes. However, intraspecific phylogenetic reconstruction unveiled two divergent lineages between specimens from North China plus Ushimado (Seto Inland Sea, Japan) and northern Japan (Asamushi and Onagawa). This conclusion was backed by an analysis of pairwise genetic distances, which showed that individuals from different lineages had relatively higher values (all above 2%). Based on knowledge of paleoenvironmental and tectonic activity in the northwestern Pacific, the two lineages might have originated during the Early Pliocene due to the isolation of the East China Sea from the Japan Sea/East Sea during that time, while the present-day distribution of these lineages have likely been influenced by the ocean current system.