Showing papers by "Qun Wu published in 2016"

Leaky-Wave Antennas Based on Noncutoff Substrate Integrated Waveguide Supporting Beam Scanning From Backward to Forward

Abstract: In this paper, we propose an approach to realize substrate integrated waveguide (SIW)-based leaky-wave antennas (LWAs) supporting continuous beam scanning from backward to forward above the cutoff frequency. First, through phase delay analysis, it was found that SIWs with straight transverse slots support backward and forward radiation of the $-1$ -order mode with an open-stopband (OSB) in between. Subsequently, by introducing additional longitudinal slots as parallel components, the OSB can be suppressed, leading to continuous beam scanning at least from $-40^\circ$ through broadside to 35°. The proposed method only requires a planar structure and obtains less dispersive beam scanning compared with a composite right/left-handed (CRLH) LWA. Both simulations and measurements verify the intended beam scanning operation while verifying the underlying theory.

Experimental validation of ultra-thin metalenses for N-beam emissions based on transformation optics

Abstract: A general design of metalenses for N-beam emissions is proposed based on transformation optics. A linear mapping function is adopted to achieve the homogeneous characterization of the transforming medium, which is therefore easy to be achieved compared with previous designs limited by inhomogeneity based on transformation optics. To verify the theoretical design, a four-beam antenna constructed with ultrathin, homogenous, and uniaxial anisotropic metalens is designed, fabricated, and measured. It is shown that the realized gain of the four-beam antenna is increased by 6 dB compared with the single dipole source, while working frequency and relative bandwidth are kept unchanged. The measured far-field pattern verifies theoretical design procedure.

Analysis and modeling of Fano resonances using equivalent circuit elements

Abstract: Fano resonance presents an asymmetric line shape formed by an interference of a continuum coupled with a discrete autoionized state. In this paper, we show several simple circuits for Fano resonances from the stable-input impedance mechanism, where the elements consisting of inductors and capacitors are formulated for various resonant modes, and the resistor represents the damping of the oscillators. By tuning the pole-zero of the input impedance, a simple circuit with only three passive components e.g. two inductors and one capacitor, can exhibit asymmetric resonance with arbitrary Q-factors flexiblely. Meanwhile, four passive components can exhibit various resonances including the Lorentz-like and reversely electromagnetically induced transparency (EIT) formations. Our work not only provides an intuitive understanding of Fano resonances, but also pave the way to realize Fano resonaces using simple circuit elements.

Experimental validation of ultra-thin metalenses for N-beam emissions based on transformation optics

Abstract: In this letter, we propose an ultra-thin transformation optics metalens to achieve N-beam emissions. Theoretical design is firstly verified by full-wave simulation. Then a four-beam TO metalens antenna is proposed, fabricated and measured to further verify theoretical approach. Compared with the single dipole source, the realized gain of the proposed four-beam antenna is increased by 6 dB, while operational frequency and the bandwidth are kept unchanged.

Design and optimization of UWB Vivaldi antenna for brain tumor detection

Abstract: An ultra-wideband(UWB) Vivaldi antenna designed to detect brain tumor is presented in this paper. By transforming the conventional two-layer Vivaldi antenna into a three-layer structure, the cross-polarization effect of antenna is sharply reduced. Based on different conductivity of brain tissues, the microwave absorption effect of brain tumors is analyzed in the end, which indicates the broad prospect of microwave imaging system in the field of tumor detection.

Anisotropic Properties of Ultra-Thin Freestanding Multi-Walled Carbon Nanotubes Film for Terahertz Polarizer Application

Abstract: Anisotropic transmission of ultrathin freestanding multi-walled carbon nanotubes (MWCNTs) film has been investigated using terahertz (THz) time-domain spectroscopy. The super-aligned MWCNTs films were fabricated by a novel method—drawing and winding carbon nanotubes on square-shaped polytetrafluoroethylene (PTFE) frame. The MWCNTs film exhibited anisotropic transmittance of THz wave depending on the alignment direction of carbon nanotubes relative to the THz wave polarization orientation, which proved that such MWCNTs film acts as an ideal polarizer in the THz regime. The degree of polarization (DOP) of 99.4% and the extinction ratio (ER) of 25.3 dB (average value) has been demonstrated for a MWCNTs film of 9- $\mu\hbox{m}$ thickness in a wide frequency range from 0.1 to 2.5 THz. Furthermore, the value of DOP and ER can be engineered expediently by controlling the film thickness. Our approach opens the possibility of MWCNTs film in application of THz optoelectronic devices.

Omnidirectional wireless power transfer system supporting mobile devices

Abstract: An efficient method for the challenge design of an omnidirectional wireless power transfer system (OWPT) is proposed. The OWPT is realized utilizing the rotating magnetic field, which is generated by the proposed 2-D transmitter. The transmitter is composed by two mutually perpendicular loops fed by two excitation sources with the same magnitude and 90° phase difference. An OWPT system prototype is fabricated and measured. Experimental results demonstrate that the system can deliver power to receivers moving around the transmitter with a steady transfer efficiency. Furthermore, the magnitude distribution of the rotating magnetic field can be controlled by the feeding phase difference between the two loops. This capability enables the OWPT system to focus energy for device moving in a limited receiving angle range.

An omnidirectional wireless power transmission system with controllable magnetic field distribution

Abstract: A design method for the omnidirectional wireless power transmission system (OWPT) is proposed. The OWPT is realized by applying the rotating magnetic field, which is generated by the proposed transmitter. The proposed transmitter is composed by two mutually perpendicular loops fed by two excitation sources with the same magnitude but different phases. An OWPT system prototype is fabricated and measured. The experimental results validate the property of omnidirectional wireless power transmission. Furthermore, the magnetic field distribution can be steered by the feeding phase difference between the two loops. This capability enable the proposed OWPT system to focus energy for receiver moving in a limited range of receiving angle.

Wideband tuning range frequency selective surface based on liquid crystal and tunable ability analysis

Abstract: In this paper, a liquid crystal tunable frequency selective surface (FSS) in S-band is proposed. The relative permittivity of liquid crystal can be changed from 2.5 to 3.3, with the change of bias voltage applied to it. In that way, the FSS proposed in the paper has a tunable feature. The full-wave simulation of the tunable FSS is carried out in the paper and the equivalent circuit model (ECM) is extracted. The SPICE-based simulation results are consistent with the full-wave simulation, which verify the validity of the ECM of the FSS. The pass band shifts from 3.612 GHz to 3.954 GHz with a relative bandwidth of 9.04% when the bias voltage of liquid crystal changes.

Planar metasurface as generator of Bessel beam carrying orbital angular momentum

Abstract: In this paper, a planar metasurface operating in microwave region to generate Bessel beam carrying orbital angular momentum (OAM) is proposed. The beam generator is realized by utilizing the abrupt phase changes at the interface of the metasurface, instead of the gradual phase differences in the optical lenses. The proposed planar metasurfaces are designed and simulated respectively, and the results show that the desired beams can be generated efficiently by using a compact planar 2-D structure.

Electrically tunable array antenna with beam steering from backfire to endfire based on liquid crystal miniaturized phase shifter

Abstract: In this paper, an electrical array antenna based on liquid crystal (LC) miniaturized phase shifter is designed and simulated, with the capability of beam steering from backfire to endfire. Special chamfered design of meander line is proposed to obtain compact phase shifter based on LC. The antenna integrates phase shifters, power dividers and patch antennas on a substrate to achieve reduced occupied area. The simulated results reveals the beam steering range is from −21° to + 15° at 12.5 GHz.

Coherent perfect absorption in an electromagnetically induced transparency-like (EIT-like) system

Abstract: We propose a scheme for realizing the coherent perfect absorption (CPA) by exploiting the moderate coupling between the electric and magnetic resonators in an electromagnetically induced transparency-like (EIT-like) system. Moreover, the ideal parity-time (PT) symmetry can be established in such a passive system by precisely engineering the rate between the scattering and dissipative losses of resonators as well as their coupling. Specifically, by controlling the phase difference between two incident waves, the absorption ratio of CPA at the peak frequency can be dynamically modulated from 1 to 0. Such a scheme provides an effective route to construct absorbing devices.

Study on near-field to far-field transformation of equipment's electromagnetic radiant field

Abstract: Some willful or unaware electromagnetic lesk and interference will influence farawary device though long distance propagation. In order to solve this EMC problem, near-field to far-field transformation method is studied by means of PWE method. With Lorentz reciprocity principle, near-field to far-field transformation, integrable couplings and compensation method are deduced. Second, sampling error during near-field measurement is analyzed. Three kinds of error are considered, which include random amplitude-phase error, finite scanning truncation error and probe positioning error. For each kind of error sources, it will be introduced into the simulation model respectively and modified by the error compensation method. Finally, electromagnetic radiation of real aircraft model is simulated and analyzed, which receives aircraft's electromagnetic radiation property on 500kHz–30MHz, 50MHz–400MHz and 1GHz.

A dual band CRLH leaky wave antenna with electrically steerable beam based on liquid crystals

Abstract: A dual band CRLH leaky wave antenna with electrically steerable beam based on liquid crystals is designed and investigated. Lots of full-wave simulations are conducted with CST MW Studio software package to optimize and analyze the performance of the antenna. It shown that the proposed LWA achieves the beam scanning from −16° to + 21° at 7.2 GHz and from −10° to + 19° at 9 GHz simultaneously, through tuning the permitivity of the LC material. Such electrically tunable dual-band LWA can be used as an effective and feasbile common antenna for the signal transmitting and receiving of satellite communication in motion.

Design and analysis of tapered-slot Vivaldi antenna

Abstract: Vivaldi antenna is widely used for ultra wide band systems because of its wide band, low cost and high directivity. In this paper, a novel Vivaldi antenna is proposed for measurement system. The design and optimization method is introduced. By applying a tapered-slot structure to the conventional Vivaldi antenna, the radiation characteristics of the antenna are obviously improved. The band width of the proposed antenna is extended to lower frequency band. The model of proposed antenna is constructed and simulated by CST and the results are in accordance with what expected and satisfy the design requirement perfectly.

Planar EBG structure for broadband suppression of simultaneous switching noise

Abstract: Simultaneous switching noise is the main reason that greatly affects power integrity of power distribution network. In order to suppress simultaneous switching noise in low frequency range and expand the stop-band bandwidth, we propose a new type planar electromagnetic band-gap (EBG) structure which is achieved by increasing the connection bridge between the patches. It can be directly embedded in high-speed circuit PCB. When the suppression depth is −30dB, the stop-band is 0.29–7.21GHz. The proposed electromagnetic band-gap structure can effectively decrease the lower cutoff frequency and expand the stop-band bandwidth which is confirmed by simulation.

An approach to predict interference of transceiver system by spectrum allocation

Abstract: In this paper, the receivers and transmitters for multi-system transceivers are modeled by spectrum allocation to predict mutual interference. The mirror interference, resonance interference, intermediate frequency interference and the local oscillator interferes have been taken into consideration as interference parameters for prediction by computer codes. Potential interference from the systems can be identified in advance by spectrum allocation to reduce complexity of EMI test and meet the requirements of system EMC performance, realizing the electromagnetic compatibility and enhancing the reliability of equipment and systems.

Electrically controlled leaky wave antenna with wide-angle scanning based on liquid crystal

Abstract: In this paper, a design method of electrically controlled leaky wave antenna based on liquid crystal is proposed and investigated. The leaky wave antenna is composed of a rectangular waveguide and an inverted PCB micro-strip structure with eight short slots. By loading bias voltage to the liquid crystal, the leaky wave antenna implements wide beam scanning on fixed frequencies. Simulation results indicate that a 36° beam scanning range is realized in Ku band.

Miniaturized frequency selective surface and broadband frequency selective surface design

Abstract: This paper presents the results of our research in the field of frequency selective surface in recent years. Aiming at the traditional passive frequency selective surface (FSS) in this paper, we mainly do two aspects of research work, which is the research of the small frequency selective surface and the research of the ultra wide band frequency selective surface. The center frequency value of the miniaturized FSS is only 2.47GHz, and the relative size of the unit is only 0.0494λ×0.0494λ and. That is to say, the unit size is less than λ/20. Stop band for the double layer structure FSS we proposed is from 11.03 to 13.98 GHz, with a relative bandwidth 23.6%. Pass band for the three dimensional structure FSS we proposed is from 8.1 to 14.6GHz, with a relative bandwidth 57.3%. The miniaturized FSS structure and wide band FSS structure have high practical application value.

Generating reflective vortex waves in microwave region by metasurface

Abstract: In this paper, anomalous reflection for circularly polarized (CP) waves is proposed to achieve, where the reflected waves possess orbital angular momentum (OAM) along their direction of propagation based on the Pancharatnam-Berry (geometrical) phase. Based on the phase gradient metasurface (PGM), we firstly presented a polarization-converting metasurface reflector for circularly polarized waves. On the basis of the reflector, two reflective vortex plates were designed. Under normal incidence, high-efficiency vortex waves are obtained by illuminating one vortex plate. Under oblique incidence, high-efficiency anomalous reflection of votex waves occurs for circularly polarized waves with 0° reflection angle by illuminating the other votex plate. The results of experiment and simulation are both accordant with theoretical prediction, which convincingly verifies the high-efficiency anomalous reflection of votex waves of CP waves. This technology makes a remarkable progress which is beneficial to put metasurface into practical application.

Metasurface in microwave region: Theory and applications

Abstract: In this paper, recent works of metasurface in microwave region are reviewed. First, ultra-thin metasurface based on phase discontinuity is introduced. Different spatial phase functions are adopted to achieve manipulation of wavefront, including bi-polarization metalens and orbital angular momentum. Second, metasurface based on transformation optics is studied. A four-beam antenna is constructed based on metasurfaces, which is verified by experimental results. Our designs provide a promising approach to miniaturize, planarize and integrate multiple microwave components.

Metasurface for polarization and phase manipulation of the electromagnetic wave simultaneously

Abstract: Metamaterials has inspired many novel physical mechanism and applications for the past decades. In these cases, the thickness of metamaterial is a must to achieve the unique electromagnetic response, which will definitely result in bulky structures and the accompanying loss, especially in microwave region. In this paper, our efforts in planar metasurface are reviewed with emphasis on manipulation of the phase and polarization state of electromagnetic wave. The latest results show that by introducing magnetic resonance between the layers of the metasurface, the polarization state and the phase of the incident wave can be fully controlled by the metasurface with a relatively high efficiency.

Modeling and EMC simulation of vehicular radio transmission antenna

Abstract: This paper presents an average complexity model of a military vehicle (Humvee) carrying a radio transmission antenna for the Electromagnetic Compatibility (EMC) simulation by using the Finite Difference Time Domain method (FDTD). Electromagnetic (EM) fields inside and nearby of the vehicle are computed. The high strength EM fields locations called hot-spot inside the cabin are investigated. Surface current on the metallic structure of the vehicle is estimated. Then the EM exposure is compared with the recommended limits defined by the RE102 directive.

Planar efficient metasurface for vortex beam generating and converging in microwave region

Abstract: In this paper, a single-layer transmission-type metasurface is proposed to generate vortex beams and converge the beam in microwave region. Utilizing the abrupt phase changes introduced by the unit cells, the required phase differences accumulated along the propagation path in conventional optical lens can be easily achieved, resulting in a planar structure of the proposed microwave lens. The results show that our design works efficiently at the operation frequency.

High selective metamaterial resonator based on complementary split ring resonator

Abstract: In this work, a metamaterial resonator based on complementary split ring resonator (CSRR) loaded with square open-loop resonator (OLR) is presented theoretically and experimentally. It is shown through equivalent circuit model that the addition of OLR to the conventional CSRR-loaded cell generates transmission zero in the upper stop band and improves the upper band rejection level without increasing the traversal dimensions. Simulation results show that a passband with high selectivity is obtained. Moreover, the via-free characteristic of the basic cell enables easy and low-cost fabrication.

Direction Finding System Using Planar Luneburg Lens

Abstract: In this paper, a novel two-dimensional Luneburg lens, composed of artificial impendence surfaces (AIS), is proposed for direction of arrival (DOA) estimation. Several detectors are mounted around the Luneburg lens to estimate the DOA of a microwave signal, owing to the surface wave can be focused perfectly on the diametrically opposite side of the lens. The desired refractive index profile of the Luneburg lens is controlled by the variable surface impendence of the unit cells, which is obtained by using an array of complementary unipolar compact photonic band gap (UC-PBG) structure inside a parallel plate waveguide. The proposed Luneburg lens with several probes, which operate in X-band region, are fabricated and measured to demonstrate the direction finding system. Both simulation and measured results show that the system has an excellent focusing ability, and the measured resolution of the system agrees very well with the theoretical value.

A half-mode substrate integrated waveguide based leaky-wave antenna with open-stopband suppression

Abstract: This paper presents a leaky-wave antenna (LWA) based on half-mode substrate integrated waveguide (HMSIW). The proposed LWA consists of transverse and longitudinal slots in one unit cell, by properly adjusting the structure parameters of the slots, open-stopband can be suppressed and hence the proposed LWA features continuous beam scanning from backward, through broadside, and to forward. Additional transverse slots are also implemented to suppress the cross polarization level. Numerical simulations are conducted and the results verify the theory very well.

A novel miniaturized frequency selective surface with stable responses

Abstract: A novel band-pass Frequency Selective Surface (FSS) working on L-band is presented in this paper. By means of the coupling effect of the metallic patches on three different layers, the distributed capacitance of the periodic structure is formed and therefore decreases the resonant frequency. Investigations on the structure variables are presented and a novel unit cell, whose size is only λ0/20, is proposed. Furthermore, the novel FSS structure has shown a quite stable response for different incident angles and polarization modes as for its symmetry and miniaturization configuration. In addition, the miniaturization performance is investigated and optimized by changing the parameter of the structure.

A Novel liquid crystal based leaky wave antenna

Abstract: A Novel electrically controllable composite right/left-handed leaky wave antennas (CRLH-LWAs) based on liquid crystal (LC) is proposed. Simulation results show the antenna exhibits a simulated beam scanning angle of −47° to +56° over the frequency range of from 11.8 GHz to 13 GHz. A simulated bandwidth from 11.78 GHz to 13.09 GHz is achieved. By steering the permittivity of LC, the antenna presents a simulated range of electrically beam steering from −21° to +23° is presented at 12.4GHz.