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A new planar microstrip-fed monopole ultra-wideband (UWB) antenna with dual notched bands has been presented. By employing a simple dual-mode resonator with two symmetrical outer high-impedance lines beside the microstrip feed line of the proposed UWB antenna, two controllable rejection bands with high-frequency selectivity are created. The parametric studies of the proposed structure are explored for the dual band-notched operating mechanism. Finally, the experimental results, including return losses, radiation patterns, and peak gains are shown, declaring that the proposed antenna has good impedance matching performance and radiation pattern properties. [ABSTRACT FROM PUBLISHER]

ABSTRACT A novel printed quasi-Yagi antenna with dual stubs loaded on a parasitic strip director has been presented. The impedance bandwidth is analyzed and compared when we add or eliminate the parasitic strip director. Then, two open stubs are loaded on the strip to excite an additional resonant mode, which lead to a wider impedance bandwidth. To demonstrate the effectiveness of this design, an antenna prototype is fabricated and tested. Experimental results show that the antenna provides a bandwidth ranging from 4.4 to 9.3 GHz and within the whole band larger than 4.1 dBi gain is achieved. Additionally, the proposed antenna presents a stable end-fire radiation directivity and low cross-polarization level at different frequencies with a compact structural size of 35 mm × 26 mm. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:447-451, 2017 [ABSTRACT FROM AUTHOR]

A T-shaped stub-loaded ring-resonator (SLRR) slot etched on the ground plane or on the radiating patch has been designed and analyzed for antenna applications. Compared with the conventional ring slot, the two resonant frequencies of the proposed SLRR-slot can be lowered, and can also be tunable by varying the parameters of the four T-shaped stubs. To validate the design concept, a tri-band printed antenna and a dual band-notched ultra-wideband (UWB) antenna using the SLRR-slot on the ground plane and radiating patch, respectively, are presented. For the tri-band antenna, a simple U-shaped slot etched on the microstrip feeding line is used to excite a third upper-frequency band independently without increasing the overall size of the antenna and without affecting the lower two bands. The proposed tri-band antenna has three frequency bands of 2.4, 3.5, and 5.8 GHz, and the dual band-notched UWB antenna can guarantee a very wide bandwidth from 3.0 to 12.0 GHz with dual undesired bands successfully. The experimental results including radiation patterns, peak gains and efficiencies of both antennas are presented. [ABSTRACT FROM PUBLISHER]

Laser range-gated imaging systems can obtain the images of targets hidden around a corner by using an intermediary reflective surface with certain specular reflection characteristics. This imaging mode is called non-line-of-sight imaging. The target signal irradiance and disturbance radiation on the photo-detector of a non-line-of-sight imaging system are analyzed based on the modeling of an intermediary reflective surface, and an image contrast model of a non-line-of-sight imaging system is constructed. The effects of the reflective characteristics of an intermediary reflective surface and the distance between the intermediary reflective surface and the target or the detector on the image quality are analyzed in terms of the parameters of a typical non-line-of-sight imaging system. The simulation results show that a laser range-gated imaging system is indispensable for non-line-of-sight imaging with commonly used intermediary reflective surfaces without significant specular reflection characteristics, and the distance of the intermediary reflective surface from the target has a significant effect on the non-line-of-sight imaging. When the locations of detector and target are fixed, the non-line-of-sight imaging system can hardly identify the target if the intermediary reflective surface is closer to the target. In practice, the performance of the non-line-of-sight imaging system can be maximized using an appropriate usage strategy. [ABSTRACT FROM AUTHOR]

Based on multi-mode resonator (MMR) and \lambda/4 resonators, a miniaturized microstrip quint-band bandpass filter (BPF) with mixed electric and magnetic coupling (MEMC) has been presented. The proposed MMR is employed to generate the 1st, 2nd, and 5th passbands, while the 3rd and 4th ones of close band proximity are achieved by using four coupled \lambda/4 uniform impedance resonators (UIRs). Due to MEMC cancelling effect, virtual grounds in feed lines, and source-load cross coupling, multiple transmission zeros (TZs) can be yielded to obtain sharp passband roll-off skirts. To verify the validity of the design approach, a quint-band BPF centering at 2.1, 3.0, 4.0, 4.7, and 7.2 GHz (denoted as f1, f2, f3, f4, and f5) with respective 3 dB fractional bandwidths of 13.7%, 5.6%, 10.5%, 5.1%, and 2.9% has been designed and fabricated, whose measured results show good consistence with the predicted frequency responses. [ABSTRACT FROM PUBLISHER]

[Display omitted] • Provided a detailed introduction on THz metamaterials for spectrum modulation. • Summarized the different structures of THz metamaterials reported previously. • Introduced various special materials used in THz metamaterials. • Summarized the applications of THz metamaterials for spectrum modulation. Metamaterials, an artificial electromagnetic (EM) material, have exhibited unique characteristics, enabling innovations in terahertz (THz) wavefront shaping, polarization modulation, surface wave manipulation, and spectrum modulation. In this review, we focus on the advancements in THz metamaterials for spectrum modulation, emphasizing their structural design, special materials, and applications. The review discusses various structural designs, including metal-dielectric composite structures, all-metal structures, and all-dielectric structures, each offering distinct advantages for THz applications. Key special materials such as graphene, vanadium dioxide (VO 2), molybdenum disulfide (MoS 2), and flexible materials are highlighted for their significant contributions to enhancing the performance and functionality of THz metamaterials. The applications of THz metamaterials in EM stealth and sensing are thoroughly introduced, with a particular focus on biosensing, pesticide detection, and other sensing applications. The review emphasizes the potential of THz metamaterials in developing highly sensitive and selective sensors, as well as efficient THz absorbers and filters. Future perspectives include the continuous development of novel materials, advanced fabrication technologies, and the integration of multifunctional capabilities to further expand the applications and efficiency of THz metamaterials. These advancements are expected to drive significant progress in THz technology, impacting fields such as medical diagnostics, environmental monitoring, food safety, wireless communication, and security. [ABSTRACT FROM AUTHOR]

This paper presents a compact multifunctional reconfigurable filter based on double coupled‐line structures with three different filtering modes. Three different working modes of the wideband bandpass filter (BPF), bandstop filter (BSF) and wideband filter with single notch can be switched. One prototype of the reconfigurable filter is constructed and measured. For the wideband BPF mode, the 3‐dB bandwidth is 84.5%with in‐band return loss (RL) higher than 21.5 dB and minimum insertion losses (IL) of 0.9 dB, and rejections for the upper stopband is higher than 22.5 dB. For the wideband filter with single notch mode, the 3‐dB bandwidth is 39.7% and 24.9%, with the minimum in‐band IL of 1.13 dB and 1.5 dB, respectively. The maximum rejections between the two bands are 32 dB, and the upper stop band rejections are higher than 19 dB. For the BSF mode, the 3‐dB bandwidth is 29.6%. [ABSTRACT FROM AUTHOR]

We numerically propose a dual-band absorber in the infrared region based on periodic elliptical graphene-black phosphorus (BP) pairs. The proposed absorber exhibits near-unity anisotropic absorption for both resonances due to the combination of graphene and BP. Each of the resonances is independently tunable via adjusting the geometric parameters. Besides, doping levels of graphene and BP can also tune resonant properties effectively. By analyzing the electric field distributions, surface plasmon resonances are observed in the graphene-BP ellipses, contributing to the strong and anisotropic plasmonic response. Moreover, the robustness for incident angles and polarization sensitivity are also illustrated. [ABSTRACT FROM AUTHOR]

This paper presents a design for a low-coupling multiple-input multiple-output (MIMO) antenna with two antenna elements. There is a dielectric resonator centrally and four inverted-F slots around on each element. This dielectric resonator consists of a dielectric block with an I-shaped metal pattern and is encircled by a metal ring with air holes. The use of inverted-F slots and the dielectric resonator effectively reduces the mutual coupling between the two antenna elements. Simulation and measurement results indicate that the designed MIMO antenna achieves a high level of isolation, maintains a low envelope correlation coefficient, and possesses a relatively high overall active reflection coefficient efficiency within the bandwidth of 6.41 GHz–6.62 GHz. These characteristics make the MIMO antenna perform exceptionally well in enhancing communication system performance, particularly in terms of signal quality, channel capacity, and system efficiency. [ABSTRACT FROM AUTHOR]

An antenna‐filter‐antenna (AFA) based frequency selective surface (FSS) with excellent spatial filtering performance is proposed. This FSS design incorporates two back‐to‐back microstrip patch antennas, which not only ensures a high roll‐off rate at the passband edge and excellent flatness within the passband, but also achieves an ultra‐low profile. Significantly, the upper and lower band edges demonstrate a substantial drop from −3 to −10 dB within the 0.006 and 0.02 GHz ranges, respectively, resulting in a sharp roll‐off skirt. Furthermore, the frequency of radiation null can be controlled by manipulating the length of the quarter‐wavelength open‐ended stub, thereby possessing exceptional out‐of‐band suppression. A prototype of the proposed FSS with low profile is fabricated and measured. The simulations and measurements of the AFA‐based FSS show that a quasi‐elliptical bandpass filtering response with superior performance is achieved. [ABSTRACT FROM AUTHOR]

In this article, a newly spoof surface plasmon polaritons (SSPPs) is proposed and used to design a compact wideband bandpass filter (BPF). Different from the traditional SSPP unit cell with one-shaped structure, the unit cell of the proposed SSPPs consists of an H-shaped slotline and a bilateral T-shaped slotline. Benefiting from the hybrid structure, no transition portion is needed for impedance matching in the design of the microwave filter, which highly reduces the horizontal size of the SSPPs-based filter. The transition structure of microstrip to slotline provides a capacitance with a highpass frequency response, which enables the realization of a passband by cooperating with the natural lowpass property of SSPPs. Also, the upper and lower cutoff frequencies of the proposed filter can be adjusted independently by the key parameters. Besides, a wide upper stopband can be obtained by properly designing the SSPPs unit cell and the microstrip to slotline structure. Finally, a well-designed BPF operated at 1.3–6.2 GHz and its upper stopband rejection reaching 20 GHz is fabricated and measured. The test results are in good agreement with the simulations, which verifies the feasibility of the proposed structure and design method. [ABSTRACT FROM AUTHOR]

The emergence of exceptional points in a non‐Hermitian system has provided intriguing possibilities to enhance the sensitivity of a sensor, while it is yet a considerable challenge to implement subwavelength non‐Hermitian systems. One possible solution to tackle this challenge is to take advantage of localized surface plasmon resonances, which enable large electromagnetic enhancement at the subwavelength scale. In this work, a novel sensing scheme based on the exceptional points in a spoof plasmonic structure working at microwave frequencies is proposed. It is shown that near‐field plasmonic vortices can be efficiently generated at the exceptional points, resulting in the enhanced sensitivity when detecting a single particle or fluid analytes. Single particle detection with the particle size as small as 1/100 of the operating wavelength is reported. For liquid analysis in the microfluidic system, the sample consumption is down to 0.72 μL. This work demonstrates the ultrahigh sensitivity of exceptional‐point‐based plasmonic sensing and opens up new possibilities for subwavelength and compact sensors operating in the microwave, terahertz, and even far‐infrared regions. [ABSTRACT FROM AUTHOR]

In this paper, a symmetrical and compact monopole multiple input multiple output (MIMO) antenna is designed with two feeding ports. To reduce the mutual coupling between antenna elements, the l -shaped stubs and the defective ground structure (DGS) are used, and additionally the chip resistors are loaded. By optimizing the length of stub, the elements isolation can be improved remarkably. Then, two rectangular slots are etched on the metal ground as DGS to change the path of electric current so as to enhance the isolation further. Also, through loading the chip resistors to control the coupling current on the stubs, the isolation can be strengthened once more. The simulation and measurement results show that this antenna has the mutual coupling of −36 dB, the envelope correlation coefficient (ECC) of 0.002 and the diversity gain (DG) of 9.99 dB at resonance along with the radiant peak gain of 4.03 dBi. [ABSTRACT FROM AUTHOR]

Based on λ /4 resonators, the synthesis design method for a miniaturized high-selectivity microstrip quad-band bandpass filter (BPF) with alternative J / K inverters has been presented. Two dual-band λ /4 stepped impedance resonators (SIRs) are employed to generate the 1st and 4th passbands, while the 2nd and 3rd passbands are achieved by utilizing four coupled λ /4 uniform impedance resonators (UIRs). Moreover, the alternative J / K inverters form is proposed to create an additional cross coupling, resulting in one pair of transmission zeros (TZs) at each side of all the four passbands. To verify the validity of the proposed method, a quad-band BPF centered at 1.9, 4.1, 4.6 and 6.1 GHz with respectively fractional bandwidths of 13.7%, 5.1%, 5.9% and 7.6% has been designed and fabricated, whose measured results show consistent match with the simulated ones. [ABSTRACT FROM AUTHOR]

This article presents a frequency–amplitude independently tunable bandpass filter (BPF). The filter uses an electrically tunable coaxial substrate integrated waveguide (SIW) resonator, which has a compact size and a constant fractional bandwidth (FBW). The surface-gap coaxial SIW resonator is loaded with eight varactors and a thin graphene sheet at the top and bottom, respectively, which results in possessing independent tuning characteristics of frequency and quality factors. The variable capacitance values of the varactor are used to achieve frequency reconfigurability, and the graphene located on the bottom surface of the resonator is equivalent to a tunable lumped resistor used to control the $Q$ -factor. In addition, detailed steps of BPF design are provided. For validation, a prototype third-order varactor–graphene-loaded multitunable coaxial SIW BPF is fabricated. The measurements show that within the tunable range of the varactors, the proposed filter can be tuned from 0.68 to 1.03 GHz with 5% ± 0.2% 1-dB FBW and the insertion loss of passband can be continuously tuned over 2.68–6.37 dB. The frequency tuning and amplitude tuning functions are not dependent on each other. Over the frequency tuning range, the transmission amplitude at an arbitrary center frequency can be dynamically tuned by controlling the bias voltage applied to the graphene. [ABSTRACT FROM AUTHOR]

A compact wideband bandpass filter (BPF) based on capacitor-loaded parallel coupled-lines and open/short stubs is presented in this brief. The proposed BPF contains four lumped capacitors that can reduce the circuit size, which are connected in series or parallel with the coupled microstrip lines and open/short stubs. Owing to the symmetry of the circuit topology structure, odd- and even-mode methods are used for analysis, then the 3-dB fractional bandwidth (FBW) and return loss (RL) can be calculated by MATLAB using impedance deduction of each branch circuit. To demonstrate the feasibility of the proposed design, a wideband BPF prototype with a center frequency of 0.23 GHz and a 3-dB FBW of 117.8 % is fabricated and measured, which exhibits a miniaturized size of 0.026λg × 0.079λg (λg: guided wavelength at the center frequency). The results of experiment are very consistent with theoretical calculations, circuit and electromagnetic simulations, validating the concept of the proposed technique. [ABSTRACT FROM AUTHOR]