Backward Beam Research Articles

Design of a low-profile bi-directional radiated Fabry-Perot cavity antenna with independent forward and backward radiation based on metasurface technique.

This paper introduces a novel Fabry-Perot cavity (FPC) antenna design based on metasurface technique to achieve bi-directional radiation with independent forward and backward beam control capability and a low-profile configuration. Two pieces of partially reflective metasurface (PRMS) based on receiver-transmitter architecture with independent control of transmission and reflection phases are designed to serve as the upper and lower layers of the FPC antenna, respectively. By manipulating the transmission phase distribution of the two pieces of PRMS, designable independent multi-beam bi-directional radiation patterns can be achieved. For validation, two FPC antennas based on the proposed configuration are designed with different bi-directional radiation patterns. Proved by simulated results, Antenna 1 can achieve forward dual-beam and backward single-beam radiation simultaneously with a return loss of less than -10 dB at 10.4 GHz. The two beams of forward radiation point in the -45° and 35° directions, respectively, with gains of 7.42 dBi and 7.70 dBi. The gain of the single beam of backward radiation is 10.82 dBi. Antenna 2 can achieve a four-beam radiation pattern with both forward and backward dual beams. The beam directions of the four beams are -153°, -44°, 37°, and 146°, respectively. The gains in each direction are 5.45 dBi, 6.63 dBi, 5.97 dBi, and 5.22 dBi, respectively. The overall profile is 23.72 mm (0.81 λ) for both antennas. The prototype of Antenna 1 is fabricated and measured. The results are in good agreement with the simulated counterparts, which demonstrates the feasibility of the proposed design methodology.

Design of Leaky Wave Antenna for V2V Communications

In this article, a low-profile, microstrip-based, periodic leaky wave antenna has been proposed for vehicle-to-vehicle (V2V) communications. The leaky-wave structure, loaded periodically with stepped impedance resonator stubs operates in the 5.4–6.2 GHz frequency band, which includes the WAVE (Wireless Access in Vehicular Environments) band (5.85–5.925 GHz) required for automated vehicular communications. The S11 obtained in the spectrum is below −12.68 dB. While the majority of the antennas designed for V2V communications produced omnidirectional patterns, the structure proposed in this work yields a directional pattern, preventing unnecessary outages of signals. The periodic structure gives an added advantage of beam scanning, resulting in a wider, yet directive coverage in the desired frequency band. A backward beam scan from −13˚ to −31˚ is obtained in the frequency range of 5.4–6.2 GHz with a gain variation of around ±0.6 dB only.

Mode attraction, rejection and control in nonlinear multimode optics

Novel fundamental notions helping in the interpretation of the complex dynamics of nonlinear systems are essential to our understanding and ability to exploit them. In this work we predict and demonstrate experimentally a fundamental property of Kerr-nonlinear media, which we name mode rejection and takes place when two intense counter-propagating beams interact in a multimode waveguide. In stark contrast to mode attraction phenomena, mode rejection leads to the selective suppression of a spatial mode in the forward beam, which is controlled via the counter-propagating backward beam. Starting from this observation we generalise the ideas of attraction and rejection in nonlinear multimode systems of arbitrary dimension, which paves the way towards a more general idea of all-optical mode control. These ideas represent universal tools to explore novel dynamics and applications in a variety of optical and non-optical nonlinear systems. Coherent beam combination in polarisation-maintaining multicore fibres is demonstrated as example.

Half-mode substrate integrated waveguide based filtering leaky-wave antenna

In this communication, a filtering leaky wave antenna based on half-mode substrate integrated waveguide (HMSIW) is proposed. The band-pass filtering response is achieved using periodic radiating slots element on high- low impedance substrate integrated waveguide. Apart from flexible filtering, the proposed antenna also shows wide range beam scanning from backward to forward quadrant of 68° in the operating frequency range of 7.7 GHz to 10.9 GHz with low dielectric material with a size of 6.73 λo. The proposed antenna is having a maximum gain of 14 dBi with gain variation of 2 dB in the operating range. To achieve continuous forward and backward beam scanning, open-stopband mitigation is necessary which is also discussed along with flexible frequency filtering.

A Low-Cost 3-D Imaging Device Using 2-D LiDAR and Reflectors

Laser techniques are widely used to perform topographic scenario surveys. However, in the absence of calibration in the Two-Dimensional (2-D)-based low-cost Three-Dimensional (3-D) scanning devices, a nonnegligible distortion between the ground truth and the reconstructed point cloud exists because of the imperfect structure of the 3-D scanning devices. Meanwhile, the real-time imaging performance is poor and insufficient to capture the shape of moving targets. Therefore, a simple but efficient 3-D scanning structure is developed to decrease the distortion. For real-time processing, the backward emitted laser beams are reflected by the reflectors and the then the reflected beams are available to detect the objects in front of the LiDAR. In the direction where objects of interest exist, the scanning frequency can be multiplied. Through a careful theoretical analysis, the spatial relationship between the points of the 2-D LiDAR, the placement of reflectors, and the 3-D objects is deduced. A solid experiment is performed in which several 3-D scanning devices are compared. It verifies the superiority of the proposed device in reducing the distortion and feasibility to alleviate the real-time processing problem.

Experimental methods for the study of spin waves

Purpose of this paper is to give an overview of various experimental methods for investigation of spin waves characteristics. Methods. The paper presents a description of a number of experimental techniques, such as the probing method, the phase shift method, the method of measure of equiphase dependences, the method of intersecting wave beams, and the use of Fourier analysis of the complex transfer coefficient of spin waves to determine their spatial spectrum. The conditions for using the listed methods and the characteristics of spin waves that one can measure by means of these methods are discussed in detail. Results. The paper presents a number of fundamental results that have been obtained on the basis of described methods. For example, the probing method was successfully used to visualize the amplitude and phase distribution of spin waves in the ferrite film plane and, in particular, it was used to experimentally confirm the previously predicted appearance of super-directed propagation of surface and backward volume spin wave beams. The phase-shift measurement method made it possible to measure the dispersion dependence of spin waves in ferrite structures such as ferrite – metal and ferrite – dielectric – metal, where measurements cannot be made by the probing method. The method of measuring equiphase dependences of spin waves made it possible, in particular, to measure for the first time with great accuracy the value of an external magnetic field magnetizing an yttrium iron garnet film to saturation in various crystallographic directions. The method of intersecting wave beams has made it possible to clarify the mechanism of parametric instability of surface spin waves. Fourier analysis of the complex transfer coefficient of spin waves allowed to determine the spatial spectrum of these waves; in particular, dispersion dependences of higher modes of the backward volume spin wave were first measured using this method. Conclusion. The methods described in this paper may continue to be successfully used for investigations of spin waves characteristics in various magnon crystals, ferrite structures and meta-structures.

Tailoring the Excited and Cutoff States of Spoof Surface Plasmon Polaritons for Full-Space Quadruple Functionalities.

Integrating diversified functionalities within a single aperture is crucial for microwave and optics-integrated devices. To date, research on this issue suffers from restricted bifunctionality, inadequate efficiency, and the limitation of extending to manipulate full-space wave. Here, we propose a general paradigm to achieve full-space multifunctional integration via tailoring the excited and cutoff states of spoof surface plasmon polaritons (SSPPs). A plasmonic meta-atom consisting of judiciously arranged metallic strips is used to excite and cut off the SSPP mode with uniaxially anisotropic characteristics. By shaping the topological structure of the meta-atom, the transmission and reflection phases are arbitrarily controlled at each pixel. Accordingly, the cross-placed meta-atom arrays can be designed to achieve independent phase profiles for x-/y-polarized transmission/reflection waves through dispersion engineering. A metamaterial with quadruple functionalities of backward beams scattering/anomalous reflection and electromagnetic transmission focusing/vortex is designed and fabricated as a proof-of-principle to reveal flexible manipulation. Both simulation and experimental verification are carried out in microwave frequency to demonstrate the feasibility.

Leaky-Wave Antenna Arrays for Flexible Dual-Beam Switching

Two novel types of dual-beam switching leaky-wave antenna (LWA) arrays based on substrate-integrated waveguides (SIWs) are proposed. The two antenna arrays consist of five SIW LWAs that work on the fundamental wave and −1st spatial harmonic wave simultaneously, so the arrays can realize fixed-frequency or frequency controlled dual-beam switching properties. The LWAs in one of the arrays have the same equivalent waveguide width and different slot periods, defined as the asymmetric dual-beam switching (ADBS) array. The LWAs in the other array have the same slot period and different equivalent waveguide widths, which is defined as the hybrid dual-beam switching (HDBS) array. The open stopbands of the arrays are suppressed by a simple structure. Using voltage-driven radio frequency chip switches (CSW-RFs) to change the excitation port, the arrays can realize the function of dual-beam switching at a fixed frequency. The measured results show that the forward beam of the ADBS array can switch from 13° to 80° while its backward beam switches from −75° to −10°, and the forward beam of the HDBS array is fixed at 45° while its backward beam switches from −10° to −80° when working at 28 GHz. Furthermore, the LWAs themselves can realize frequency-controlled ADBS in each excitation state. Therefore, the proposed arrays exhibit excellent performance in flexible dual-beam switching, which can be used in millimeter-wave applications where fixed-frequency beam switching or frequency-controlled beam switching is required.

Highly efficient few-cycle laser wakefield electron accelerator

A significant part of the laser wakefield acceleration (LWFA) research effort focuses on studying high-energy, quasi-monoenergetic electron beams. For other applications, such as the production and application of intense betatron x-ray radiation, Bremsstrahlung γ-rays and positron beams, the beam’s spectral quality is secondary to the number of electrons produced. This work discusses 3D particle-in-cell simulations of a highly efficient LWFA acceleration process, generating a broad spectrum of electrons, driven by a 12 TW few-cycle laser on high-density gas targets. In some cases, laser absorption in plasma exceeds 80%, and up to 27% of the driving laser energy is transferred to electrons over 20 MeV leaving the plasma. We also observe a deceleration of the accelerated beam at the plasma downramp and plasma exit, which arises from transitioning from laser-driven to beam-dominated wake, and also from the induced axial electric field. This effect is similar to magnetic vortex acceleration, where the induced axial electric field, instead of accelerating plasma ions, would slow down the opposite-charged electron beam and also a strong return current and backward electron beam.

Tilted-Beam Antenna Based on SSPPs-TL with Stable Gain.

In this paper, a titled-beam antenna based on spoof surface plasmon polaritons (SSPPs) transmission lines (TLs) is proposed. The parallel SSPPs-TL is a slow-wave TL, which is able to limit waves in the TL strictly. By periodically introducing a set of tapered stubs along the SSPPs-TL, the backward endfire beams are formed by the surface waves in the slow-wave radiation region. Then, through the placement of a big metal plate below the endfire antenna, the backward endfire beams are tilted, and the tilted angle of the beams are steered by the distance of the metal plate and antenna. Over the band of 5.7 GHz~7.0 GHz, the tilted antenna performs constant shapes of radiation patterns. The gain keeps stable at around 12 dBi and the 1-dB gain bandwidth is 20%. The measured results of the fabricated prototypes confirm the design theory and simulated results.

Design, Beam-Wave Interaction, and Efficiency Enhancement Studies of Millimeter Wave Gyro-TWT With a Three-Stage Depressed Collector

In this article, a $W$ -band gyrotron traveling wave tube (gyro-TWT) amplifier that uses periodically dielectric-loaded (PDL) waveguide and operates in TE01 mode is designed and studied for its stability against backward wave oscillations and beam wave interaction behavior. The subassemblies including a magnetron injection gun using E-GUN code, RF output window, and electron collector using “MAGIC 3-D” are investigated. The present particle-in-cell (PIC) simulation of millimeter-wave gyro-TWT results in a peak RF power ~195 kW in TE01 mode with an electronic efficiency of ~28% and a saturated gain of ~63 dB. Further, the overall efficiency of the device is enhanced by using a three-stage depressed collector, which is designed and simulated using “MAGIC 3-D. ” The collection efficiency of the present collector is calculated as ~74% and the overall efficiency of the gyro-TWT is improved to ~60%.

Dual‐band dual‐polarized leaky‐wave structure with forward and backward beam scanning for circular polarization‐flexible antenna application

AbstractIn this paper, a novel dual‐band dual‐polarized leaky‐wave antenna (LWA) with polarization diversity is proposed using half mode substrate‐integrated waveguide (HMSIW)‐based technology. HMSIW LWAs are generally single band. In this work, by etching simple spiral type slots on the HMSIW cavity, a novel dual‐band dual‐polarized LWA is designed. The proposed antenna resonates at 5.6 and 8.5 GHz. Moreover, the antenna radiates the linearly polarized wave in the lower band and circularly polarized (CP) wave in the higher operating band. Also, in the higher operating band between 8.7 and 9.3 GHz, the proposed overall antenna exhibits both right‐hand circular polarization as well as the left‐hand circular polarization in the near main beam direction. The −10 dB impedance bandwidth of the proposed antenna at the lower and the higher operating bands are 27% (4.86‐6.4 GHz) and 25% (7.4‐9.6 GHz), respectively. In the higher band, the 3‐dB axial ratio bandwidth of 6.6% (8.7‐9.3 GHz) is achieved. The main beam of the antenna can be steered from 19° to 69° in the forward direction in the lower operating band. In the higher operating band, the antenna can steer the CP beam between −17° and −32°. In both the lower bands, the realized peak gain is observed around 13.3 dBi, whereas in the higher band, the realized peak gain is observed around 14 dBi.

Suppression of backscattering-induced noise in a resonator optic gyro by the dual-frequency modulation method

Backscattering noise is one of the main noises affecting the accuracy of resonant optical gyroscope (ROG) systems. A method of suppressing backscattering noise in a ROG is demonstrated using a dual frequency modulation technique. On the premise of obtaining the Sagnac frequency difference, the frequency interval between the forward and backward beams is increased. Among them, high frequency modulation is used in the frequency-locked circuit, low-frequency modulation is used in the output path and the modulated optical components have a certain frequency difference. Firstly, the frequency difference between the clockwise and counterclockwise optical paths is increased by high and low frequency modulation to increase the carrier rejection ratio, and the noise generated by backscattering and signal light is suppressed. Then, bandpass filtering is used to eliminate the noise caused by the backscattering itself. Through theoretical analysis and experiment, the feasibility and effectiveness of the scheme are verified. The method effectively improves the output precision of the gyro, and the final output of the gyroscope reaches 0.0054∘/s (10 s integration time).

Observation of giant gain and coupled parametric oscillations between four optical channels in cascaded four-wave mixing

In this work, we explore both the internal and external atomic degrees of freedom to demonstrate the observation of giant gain and parametric oscillation in multiple four-wave mixing (FWM) processes in a sample of cold cesium atoms. We employ a standard backward FWM beam configuration to achieve parametric probe-beam gains exceeding 2000. This giant gain is accompanied by the generation of three other beams of equivalent power emitted along the directions satisfying the phase-matching conditions for multiple cascade forward and backward FWM triggered by the incident probe and the counterpropagating pumping beams. Moreover, we have also observed a simultaneous threshold for parametric oscillation of the four coupled optical fields with the pump intensity. These results point to an alternative pathway to generate multipartite correlated optical fields associated with long-lived atomic systems for applications in quantum information.

Multibeam Bidirectional Wideband/Wide-Scanning-Angle Holographic Leaky-Wave Antenna

This letter shows experimentally the realization of a high-gain multibeam bidirectional radiation in a wide frequency range via a planar holographic leaky-wave structure where the beams can scan from backward to forward direction as the frequency varies from 12 to 18 GHz. To realize these two key features, i.e., wideband characteristic and bidirectional multiple-beam pattern, we exploit the characteristic of a wideband surface wave launcher and inherent nature of a metasurface supporting TE mode at the same time. In more detail, this antenna benefits from a TE-mode antipodal Vivaldi as a distinguished feed, which has a broadband behavior, on a surface without metallic ground plane and realizes a high-gain bidirectional multibeam pattern. A four-beam linearly polarized antenna, including two backward and broadside beams in front side and two backward and broadside beams in the back side of the antenna is designed, fabricated, and tested at 12 GHz. The measured gain, sidelobe level, cross polarization, efficiency, and 3 dB bandwidth of the gain, are 17.8 dBi, −17 dB, −30 dB, 26.5%, and 43.3%, respectively, which are great achievements. Moreover, the maximum scan angle of $\text{44}^\circ $ , i.e., from $({\boldsymbol{\theta },\boldsymbol{\varphi }}) = ({\text{30}^\circ,180}) $ to $({\boldsymbol{\theta },\boldsymbol{\varphi }}) = ({\text{14}^\circ,\text{0}^\circ})$ , is achieved for the backward beams when the frequency varies from f = 12 GHz to f = 18 GHz.

Planar Beam Steerable Parasitic Array Antenna System Design Based on the Yagi-Uda Design Method

A planar beam steerable array antenna system is proposed with dual-control circuits for feeding and reactive loadings. Two orthogonally arranged planar dipoles are excited by SPDT switching circuits, while the forward and backward beam directions are controlled by the adjusted effective electric lengths of the parasitic dipole elements. The adjusted parasitic dipoles are designed to play the alternative roles of directors and reflectors based on the Yagi-Uda antenna theory. The proposed antenna system with four-way switchable beams has been implemented on a planar substrate and evaluated for orthogonal four-way beam steering performance with good agreement.

A Plasma Focus device as ultra-high dose rate pulsed radiation source. Part I: Primary electron beam characterization

A Plasma Focus is a device able to generate in the pinch phase several kinds of radiation fields. One of them are the backward emitted electron's beams that can be used as source for X-ray pulses generation through the interaction with a suitable target. The worth of this source stands on two elements: first, being connected to the lifetime of the pinch phase, the electron current lasts a few tens of nanoseconds, we can say 50 ns as reference; second, the electron bunches carry a charge of the order of 0.1 mC. These two aspects grant the generation of X-ray pulses of extremely short duration, while the quite strong charge bunches allow a potential dose transfer by the X-rays in the order of 1 Gy per pulse. These characteristics have made this source of interest with respect to possible medical applications, in particular for radiotherapy of superficial tumors, given also that the extremely high dose rate could be of help in winning radio-resistance of specific cancer cells as in the case of melanoma.In this first part of the work, after a brief outline of the PF working principles, the experimental techniques used for the detection and the analysis of the characteristics of the primary electron source have been described. The results showing their correlation with the capacitor's bank energy and the possible scaling laws that could drive the setup of specific X-ray generation devices for radiotherapy treatments have been thoroughly discussed.

Nonreciprocity of backward volume spin wave beams excited by the curved focusing transducer

The focusing effect for spin waves excited by a curved micrometer-sized coplanar waveguide transducer on top of a 5-μm-thick epitaxial yttrium iron garnet film is studied by means of the micro-focused Mandelstam-Brillouin light scattering technique and micromagnetic simulations. The curvilinear transducer is designed to focus the backward volume spin waves on the in-plane bias magnetic field applied along the symmetry axis of the transducer. We show that two-dimensional maps of spin wave intensity exhibit nonreciprocal properties without mirror symmetry with respect to the magnetic field direction and the focusing effect. The observed effects are the consequence of nonreciprocity of the backward volume spin waves travelling at an angle toward the bias field direction.

Experimental investigation of the detection and location of a target in layered media by using the TR-RTM mixed method

Targets in layered media can be detected and located using a time reversal (TR)-reversed-time migration (RTM) mixed method. In this study, this single emission-multiple receiving method is tested experimentally by using two types of layered media and three types of targets. The signal reflected at the interface and the signal scattered by the target are measured by each receiver to obtain the travel time for several transmitter-receiver pairs. Thereafter, the amplitude ratio between the two measured signals is compared with the theoretical amplitude. The RTM process involves the convolution of the forward acoustic beam from the source with the backward acoustic beam from the receiver which adds an appropriate delay determined on the measured travel time data. By using this approach, the acoustic field distribution can be obtained, and the position of the target can be determined. Moreover, the measured positions of the target are compared with the actual position to validate the accuracy of this technique.

Dual-Band Leaky-Wave Antenna Based on Dual- Mode Composite Microstrip Line for Microwave and Millimeter-Wave Applications

A dual-mode composite microstrip line (DMC-MSL) is reported in this paper for the purpose of designing dual-band antennas and devices with a large frequency ratio. The metallic strip of the conventional MSL is replaced with a substrate integrated waveguide (SIW) arranged into a thin dielectric laminate, which leads to that two modes operating in different frequency bands, i.e., the quasi-TEM mode and the TE10-like mode, can propagate along the transmission line structure simultaneously. The DMC-MSL with a dual-layered planar configuration combines the merits of the MSL and the SIW. In addition, by adjusting the permittivity of the dielectric laminate used for realizing the thin SIW, the frequency ratio of the two operating modes can be varied flexibly. Based on the DMC-MSL structure, a novel dual-band leaky-wave antenna is presented. Periodic parasitic microstrip patches and the transverse slot array etched on the SIW are introduced in order to generate the required spatial harmonics. A feed structure that can excite the two operating modes of the DMC-MSL separately is designed as well. The fabricated prototype verifies that backward and forward frequency-scanning radiation beams are achieved within the low-frequency band from 5.75 to 8.5 GHz and the high-frequency band from 35 to 41.5 GHz, respectively. The proposed DMS-MSL structure and the leaky-wave antenna offer a new mean to implement antennas and devices for microwave and millimeter-wave dual-band applications.