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This paper presents an innovative technique to synthesize a virtual antenna array (VAA) that consumes less energy than conventional antenna arrays that are used in mobile communications systems. We have shown that for a specific spectral efficiency a wireless system using the proposed virtual antenna array consumes significantly less energy per bit (∼3 dB) than a wireless system using a conventional multiple-input multiple-output (MIMO) array. This means the adoption of the proposed VAA technology in smartphones, iPad, Tablets and even base-stations should significantly reduce the carbon footprint of wireless systems. The proposed VAA is realized by employing a pair of linear antenna arrays that are placed in an orthogonal configuration relative to each other. This orthogonal arrangement ensures the radiation is circularly polarized. The size of the standard radiating elements constituting the VAA were miniaturized using the topology optimization method. The design of the VAA incorporates substrate integrated waveguide (SIW) and metasurface technologies. The function of SIW in the design was twofold, namely, to reduce energy loss in the substrate on which the VAA is implemented, and secondly to mitigate unwanted electromagnetic interactions between the neighboring radiating elements and thereby enhancing isolation which otherwise would degrade the radiation characteristics of the array. Metasurface technology served to effectively increase the effective aperture of the array with no impact on the footprint of the array. The consequence of SIW and metasurface technologies was improvement in the gain and radiation efficiency of the array. The proposed four orthogonal 4-element VAA covers the entire sub-5 GHz frequency range, and it radiates bidirectional in the azimuth plane and omni-directional in the elevation plane. Moreover, it is relatively easy to design and fabricate. The proposed VAA has dimensions of 0.96λ0 × 0.96λ0 × 0.0016λ0 at mid-band frequency of 3 GHz. VAA has a measured gain of 25 dBi and radiates with 90% efficiency. The average isolation between the linear arrays constituting the virtual array is better than 27 dB. Dr. Mohammad Alibakhshikenari acknowledges support from the CONEX-Plus programme funded by Universidad Carlos III de Madrid and the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 801538. The authors also extend their appreciation to the Deputyship for Research & Innovation, Ministry of Education in Saudi Arabia for funding this research work through the project number 223202. Additionally, this work was supported by Ministerio de Ciencia, Innovación y Universidades, Gobierno de España (Agencia Estatal de Investigación, Fondo Europeo de Desarrollo Regional-FEDER-, European Union) under the research grant PID2021-127409OB-C31 CONDOR.

In this work, dual-band perfect absorption performance with high Q-factors is achieved in terahertz frequencies by the proposed metamaterial absorber.

A compact but very simple dual-band bandpass filter (BPF) based on just five pairs of coupled lines is designed in this paper. It can be examined using the even- and odd-mode method because of its symmetry structure. Six transmissions zeros (TZs) can be obtained and calculated by using input impedance analysis. For demonstration, a dual-band narrowband BPF example with center frequencies at 0.94 and 1.12 GHz is fabricated and measured. The 3-dB fractional bandwidths of two passbands are 2% (0.93–0.95 GHz) and 3.4% (1.1–1.14 GHz), whose frequency ratio of upper-band to lower-band is very small. The measurement results agree with the simulation results, confirming the design process.

In this paper, two simple structures, i.e., coupled line and T-shaped microstrip structures, are used to construct four types of quasi-reflectionless (QR) filters, including single-and two-port QR bandpass filters (BPFs) and bandstop filters (BSFs). First, the characteristics of the coupled line and T-shaped microstrip structures are analyzed in details using each two electrical parameters. Then, the single-port QR BPF and BSF are designed using duplexer architectures formed by these two simple structures. Subsequently, the two-port QR BPF and BSF are constructed through loading an additional absorption channel near the output port based on the architectures of single-port QR filters. The relations between the fractional bandwidth (FBW) of each type of QR filters and 3-dB FBWs of the two simple structures are provided, which give a guidance of the QR filter design with desired specifications. Moreover, a brief design procedure for the proposed QR filters is summarized. Finally, to validate the feasibility of the proposed approach, two proof-of-concept microstrip prototypes of the two-port QR filters are fabricated, whose simulations and measurements agree well with each other. This work will facilitate the design of QR filters with different desired specifications and simplify their design procedures.

A W-band E-plane waveguide BPF is proposed using an embedded substrate with two metal strips and a meander ring resonator. The center frequency, bandwidth and skirt selectivity of the proposed BPF can be easily adjusted. A simplified LC equivalent circuit is given to understand the operational mechanism of the BPF structure and investigate the distributions of the transmission zeros and poles. To validate the idea and show the performance of the designed W-band BPF, a prototype example is manufactured and measured. The measurement results show that the waveguide BPF has a center frequency at 91.3 GHz with a bandwidth from 88.9 to 93.7 GHz, and the minimum insertion loss within the passband is 1.6 dB.

Two compact spoof surface plasmon polariton (SSPP) waveguides are proposed with simple configurations and good performance. Compared with the conventional SSPP structure having same asymptotic frequency, a new design of the tilted-stub structure occupies less transversal space. Moreover, this design can be applied in the SSPP cases with small period values, which will facilitate the longitudinal miniaturization. Then, an improved SSPP structure is constructed to realize the transversal size reduction of 58% compared with the conventional corrugated SSPP waveguide. For these two proposed waveguides, smooth transitions from microstrip lines to SSPPs are designed with seamless connection. Two experimental prototypes have been fabricated, whose measurements are in good agreement with the simulated ones. The proposed designs will have significant potentials for the miniaturization of plasmonic devices and circuits.

A coplanar waveguide (CPW) based spoof surface plasmon polariton (SSPP) waveguide with strong field confinement is proposed, which has a low-pass filtering response. Then, two half-wavelength slot resonators are loaded on both sides of the SSPP waveguide to introduce a notch in the passband. Meanwhile, the SSPP waveguide with two ring slot resonators is simulated, whose results are consistent with the SSPP low-pass filter. Finally, two PIN diodes are bridged across the slits of the two resonators to realize the dynamic switchability of the notch. The waveguide functions as a notch filter when the diodes are in on-state, and a low-pass filter when the diodes are in off-state. To verify the feasibility of the design, a SSPP waveguide example is fabricated and measured, where the simulated and measured results are in reasonably good agreement.

A high-selectivity bandpass filter (BPF) based on two merged ring resonators is presented in this paper. The structure of this proposed BPF can be seen as the two one-wavelength ring resonators merged each other by sharing the common λg/2 microstrip line. Due to symmetric structure, it can be analyzed by even- and odd-mode method and the locations of six transmission zeros are calculated using input impedance deductions. For further demonstration, a BPF example centered at 2 GHz is fabricated with high frequency selectivity. The measured 3-dB fractional bandwidth is 11% (1.89-2.11 GHz) and insertion loss is less than 2 dB in the passband. Good agreement between simulation and measurement verifies the feasibility of the design method.

A 60-GHz compact dual-mode on-chip bandpass filter (BPF) is presented using gallium arsenide (GaAs) technology. To demonstrate the working mechanism of the proposed BPF, an LC equivalent circuit model is conceived and analyzed for further investigation of the transmission poles and zeros. Finally, a prototype of the BPF is fabricated and tested to validate the proposed idea, whose simulated and measured results are in good agreement. The measurements show that it has a center frequency of 58.7 GHz with a bandwidth of 18.4%, and the minimum insertion loss within the passband is 2.42 dB. The chip size, excluding the feedings, is about 0.158 mm $\times0.344$ mm.

In order to understand the growth dynamics of为更精准地掌握浙江沿岸春秋季小黄鱼生长动态,本文利用2014—2019年春季(4月)和秋季(11月)在浙江沿岸海域底拖网调查资料,通过构建一个广义线性模型(GLM)和9个线性混合效应模型(LMEM)来研究小黄鱼生长的异质性。结果表明:小黄鱼平均体长为124.12 mm(15～210 mm),优势组为110～140 mm;平均体重为33.28 g(0.04～156.2 g),优势组为30～50 g。根据AIC最小准则,同时具有季节和水域对生长参数

A compact multifunctional switchable filter based on parallel-coupled lines with three different filtering functions is presented in this letter. By using p-i-n switches to connect or disconnect microstrip line and shorted coupled lines, three different modes, i.e., wideband bandpass filter (BPF), bandstop filter (BSF), and dual-band BPF, can be realized. For demonstration, the switchable filter prototype is designed and fabricated. For the wideband BPF mode, the measured 3-dB fractional bandwidth is about 53.1% (1.41–2.43 GHz) with the measured insertion loss of 0.9 dB. For the BSF mode, the measured 10-dB fractional bandwidth is about 30.2% (1.63–2.21 GHz) with in-band suppression level of over 15.5 dB. For the dual-band BPF mode, the measured 3-dB bandwidths of the two passbands are around 3.8% and 2.7%, respectively.

In this letter, high-order mode dispersion of a novel spoof surface plasmon polariton (SSPP) unit cell is reported, which has excellent bandpass propagation feature. Its asymptotic frequency and intersection frequency with light line can be independently manipulated by changing the geometric parameters of the slot in proposed SSPP unit cell. In order to validate the feasibility of high-order mode of SSPPs applied in the design of bandpass filters, two SSPP waveguides based on the method with different bandwidths are fabricated and measured. No mode-conversion transition part is introduced in the procedure of waveguide design which avoids extra addition of layout area and reduces complexity of devices. The measurements show that the proposed SSPP waveguide based on high-order mode characteristics can achieve bandpass signal propagation smoothly with controllable bandwidth.

In this letter, a GaAs-based wideband spoof surface plasmon polariton (SSPP) waveguide with super compact size is presented at millimeter-wave regime. The periodic SSPP unit cell consists of a longitudinal slot and a meander slot in transversal direction, and its corresponding waveguide has good low-pass filtering feature. The momentum of microstrip line for measurement feeding to the SSPPs can be well matched without any gradient transition structures. To apply this SSPP waveguide into the design of bandpass filter (BPF), a row of vias is added with a certain distance from the SSPP unit cells. For demonstration, two on-chip examples, i.e., SSPP waveguide and SSPP-based BPF, are fabricated operating at different frequencies. Good agreement between simulations and measurements validates the propagation characteristics and implementation of the proposed SSPPs.

A bandpass filter (BPF) with a notched band is designed based on the high-order mode of spoof surface plasmon polaritons (SSPPs). The high-efficiency passband is developed from the first high-order mode (Mode 1) of SSPPs. Compared with the fundamental mode having low-pass response, the Mode 1 has the inherent bandpass response; thus, the BPF generated by Mode 1 does not need to add an additional high-pass filtering structure and employ a gradient transition structure for excitation. The Mode 1 of SSPPs can be effectively excited just with a simple trapezoidal transition converting the signals from microstrip line to SSPP waveguide. Moreover, by embedding a U-shaped resonator into the SSPP structure, a BPF with a notched band is constructed, where the location of the notched band will be red-shifted as the length of resonator increases. The measurements of two fabricated prototypes agree with the simulated ones, which verify the feasibility of our design.

A novel synthesis method is proposed to design multi-band bandpass filters (BPFs) using an L-C ladder prototype lowpass filter loaded with two symmetric shorted stubs. The transmission zeros (TZs) are produced by the shorted stubs, which are used to realize multiple passbands. By controlling the number of the open stubs loaded on the shorted stub, the number of TZs is exactly determined. Therefore, multi-band BPF is easy to be obtained by increasing the number of the open stubs. The TZs can be adjusted by optimizing the L-C values of the equivalent circuit of the proposed filter to tune the center frequencies of each passband independently. The proposed BPF also has wide upper stopband. For demonstration, an octa-band BPF is designed and manufactured. The measured results show good agreement with the simulated ones.

IEEE A refined extended alternating convex optimization (REACO) method is presented to synthesize multibeam sparse circular-arc antenna arrays with minimum element spacing control by considering real antenna array structure characteristics. This method consists of initial step and a few refining steps. At the initial step, an initial array with dense elements distributed on a circular-arc is considered, and its array manifold vector is described by rotating a simulated isolated element pattern (IEP) without considering element mutual coupling. The collective excitation coefficient vector (CECV) and its energy bound are introduced for each element, and consequently the common element positions for generating desired multibeam patterns can be found by minimizing the number of active CECVs under multiple constraints. This minimization problem is further formulated as performing a sequence of alternating convex optimization (ACO) in which the CECV and an auxiliary weighting vector are alternately chosen as the optimization variables, so that the mimimum element spacing constraint can be easily dealt with. Once the initial optimization step is finished, a few refining steps are performed in which the element positions and excitations are successively updated in each step by renewing the array manifold vector through rotating the simulated nearby active element patterns (AEPs) of the antenna array obtained at the previous step. In such a way, the mutual coupling can be incorporated into the multibeam sparse array synthesis. An example of synthesizing a sparse circular-arc conformal array with 23 beams covering the space from–63.25° to 63.25° is conducted to validate the effectiveness and advantage of the proposed method.

In this paper, a dual-band terahertz absorber based on metamaterial structure is designed, fabricated, and measured. The metal periodic array is located on the upper surface of a silicon wafer with a metal ground plane, while the metamaterial structure is created utilizing a square metal ring with four T-shaped metal strips loaded inside of the ring. Two absorption peaks are realized at 0.715 and 1.013 THz with high Q-factors of 152.1 and 98.3, respectively, under normal TE and TM polarized incidence. A prototype of the proposed metamaterial absorber is fabricated by electron beam lithography (EBL) and electron beam evaporation (EBE) technology. Furthermore, a terahertz time-domain spectroscopy (TDS) measurement system is employed to test the absorber sample, with good measurement results obtained. This work provides a new option for the design of multi-band terahertz metamaterial absorbers.

A compact millimeter-wave on-chip sensor for dielectric detection is presented using gallium arsenide technology based on spoof surface plasmon polaritons (SSPPs). The proposed structure is developed from traditional half-mode substrate integrated waveguide (HMSIW) and its dispersion characteristics is analyzed through electromagnetic simulations. Consequently, the operating frequency and bandwidth of the on-chip sensor can be easily adjusted, which provides more flexibility for the practical application of the sensor. The linear sensing for relative dielectric constant of the film materials is acquired, with thickness-insensitive property. Moreover, the low coupling to the nearby components can be achieved due to the strong field confinement characteristics of the SSPPs, which is of great significance in the application scenarios of on-chip integrated circuits for the suppression of electromagnetic interference.

Oyster reef habitats in estuarine areas are an important marine ecosystem globally. Due to the destruction of oyster reef habitats within the Luanhe River estuarine area, Bohai Sea, China, a local fisheries company created 2 km2 of artificial oyster reef habitats by deploying artificial reef blocks that provided a settling surface for a natural oyster population and conducted sea cucumber aquaculture. The aims of this study are to help fisheries managers to understand whether the ecosystem function of created oyster reef habitat is consistent throughout the seasons and to assess if the current fishing production policy which varies with seasons is reasonable. We presented steady-state trophic models in different seasons of a newly created artificial coastal oyster reef within the Luanhe River estuary to address the above issues. We concluded that seasonality is an important factor that needs to be carefully considered in the fisheries management of oyster reef ecosystems.

In this article, a new spoof surface plasmon polariton (SSPP) waveguide developed from traditional coplanar waveguide (CPW) is proposed. The asymptotic frequency of the SSPP unit cell can be easily manipulated by changing the meander groove dimensions of the SSPPs. A simple and efficient mode-conversion structure with gradient groove lengths is designed on the CPW’s ground to match the momentum of CPW to the proposed SSPPs smoothly. The designed SSPP waveguide has a good low-pass filtering property with cut-off frequency at 10.4 GHz. On this basis, another improved SSPP waveguide based on conventional grounded CPW (GCPW) is constructed, where a defected ground structure (DGS) is employed on the bottom layer of the circuit. Compared with the above work, this design has a lower cut-off frequency (8.9 GHz) and stronger field confinement. In order to validate the propagation performance, both SSPP waveguides are fabricated and measured. The measurements show that the GCPW based SSPP waveguide can effectively reduce the cut-off frequency. Such results are of great significance to the miniaturizations of plasmonic devices in microwave regime.

Terahertz communications demonstrate advantages of wide bandwidth and low latency compared to the microwave counterparts but suffer from high propagation loss in the air. Little research focuses on long-distance (i.e., distance>1 km) terahertz propagation characteristics in the air, posing challenges on long-distance terahertz wireless applications. In this paper, the terahertz long-distance propagation characteristics are explored and studied with the help of the measurement system operating at 220 GHz. Based on the measurement systems, we conduct out-door experiments with a propagation distance of 2.5 km to obtain the terahertz propagation loss in the air. Additionally, a comparison between the measured propagation loss and the calculated one based on models issued by the international telecommunication union (ITU) shows an intrinsic loss gap between these two results, which is found and explained for the first time in the above-100 GHz long-distance communication applications. With the analysis of the collected data, we propose a gap-compensation method to obtain a more accurate prediction for the propagation loss in the air. With the help of the proposed systems and corresponding measurements, we could give insight into the terahertz propagation and pave the way for future terahertz long-distance applications.

This article presents a new decoupling and matching network (DMN) design for symmetric, single- and dual-band two-element antenna arrays. The DMNs use parallel-line-based coupling elements. The decoupling between the output ports of the proposed DMN and the reflection coefficients at these ports is obtained using the scattering parameters of the coupled antenna array and those of the DMN. These are clearly expressed as functions of the DMN's design parameters. These design parameters are determined using a simple numerical method to provide high inter-element isolation and good impedance matching for the array. To verify the proposed synthesis procedure, three DMN example designs are considered. These include one for a single-band array and two for dual-band arrays having different frequency ratios. Prototypes of these antennas along with their DMNs were designed, fabricated, and experimentally characterized. In each case, a good agreement between the measured and theoretical results is achieved. Simulation and measurement results show that the proposed DMN design and its associated synthesis procedure can be employed to significantly improve the interelement isolation of single- and dual-band, two-element arrays in various scenarios.

A gallium arsenide (GaAs)-based millimeter-wave broadband bandpass filter (BPF) is proposed based on slotted half-mode substrate integrated waveguide (HMSIW) spoof surface plasmon polaritons (SSPPs). The center frequency and bandwidth of this SSPP-based on-chip BPF can be easily controlled by tuning the geometry dimensions of the SSPP unit cell, which is attributed to its unique dispersion characteristics. For demonstration, a prototype of the proposed BPF is fabricated and experimentally characterized, with good agreement between the simulated and measured results. Due to the ability of the strong electric field confinement, the proposed on-chip SSPP structure has lower coupling feature with closely-spaced transmission line circuits than its counterpart traditional HMSIW structure.