Dual-beam Radiation Research Articles

Reconfigurable Dual-Beam Lensing Utilizing an EBG-Based Anisotropic Impedance Surface

An anisotropic impedance surface based on electromagnetic bandgap (EBG) theory is proposed to produce reconfigurable dual-beam radiation through surface-wave (SW) lensing by controlling SW propagation across the surface-to-air interface. The reconfiguration of the lensing effect is triggered by switching between 4.0- and 4.5-GHz frequencies, utilizing the anisotropy of the impedance surface created from two mutually exclusive EBGs along the two orthogonal spaces. The bandgaps are formed by a periodic arrangement of two different split-ring resonators (SRRs) with bandgaps at around 4.0 and 4.5 GHz along the orthogonal y- and x-axes, respectively, producing a strong axially symmetric anisotropy. As a result, a surface-bound wave, i.e., both transverse electric (TE) and transverse magnetic (TM), faces asymmetric propagation reluctance toward these two directions one of which is very high compared to the other at frequencies around the individual bandgaps of the unit cells. The proposed impedance surface is designed and simulated using commercial electromagnetic simulation software and then fabricated and measured to validate the model.

Dual-Beam Antenna Using Routing of Electromagnetic Waves by Single-Epsilon-High Anisotropic Medium at 28 GHz

This article presents the electromagnetic (EM) wave routing technique using single-epsilon-high (single-EH) anisotropic medium to generate dual-beam radiation at 28 GHz band for next generation communication systems. This technique is implemented using SIW dipole antenna loaded with the single-EH anisotropic medium realized using modified asymmetric electric- LC (ELC) metamaterial unit cell loaded vertically in front of the radiator. The technique is first verified using simulations and then practically realized, and the results are in good agreement with the predicted theoretical results. The effect of the thickness of the media loading the antenna is investigated and dual-beam radiation in the frequency band 26–31 GHz is obtained by choosing the appropriate number of ELC-slabs. The measured results confirm 26–31 GHz impedance bandwidth and dual-beam radiation directed along 50° and 130° with 8 dBi beam peaks.

Development of a dual ion irradiation facility for studies of radiation response in fission and fusion reactor materials

A dual ion beam radiation facility which provides co-implantation of heavy ion beams from a 1.7 MV accelerator and gaseous ions from an indigenously built 400 kV accelerator has been developed. Various aspects of the dual beam irradiation facility such as the beam optics design, electronics and instrumentation comprising of a distributed control system and details of the experimental end station have been discussed. Experiments to determine essential parameters for the conduct of dual irradiation such as the beam energy spread, the spatial and the depth overlap of both beams have been carried out. For a dpa rate of 1 × 10−3 dpa sec−1 the maximum He:dpa rate achieved using this system is 50 appm dpa−1. This facility enables us to study the effect of a combination of large levels of transmutant helium and displacement damage (dpa) on the dimensional stability and mechanical properties of structural materials, He/dpa ratios on swelling in advanced alloys and co-operative effects of nuclear and electronic energy losses in nuclear structural materials.

Passive Beam Switching and Dual-Beam Radiation Slot Antenna Loaded With ENZ Medium and Excited Through Ridge Gap Waveguide at Millimeter-Waves

A unique antenna design is presented to implement the dual-beam radiation simultaneously in both H- and E-planes for operation over 57-64 GHz. The slot antenna is excited through a ridge gap waveguide. The dual beam is realized by employing arrays of anisotropic epsilon-near-zero (ENZ) structures that are located vertically over the slot antenna. The proposed ENZ medium behaves analogously to a meta-lens, and consists of meander-line H-shaped unit cells printed on the host substrate with a permittivity of 2.2. Measured results confirm that the dual-beam radiation from the antenna has maxima at ±30° with respect to the broadside direction with a maximum gain of 10 dBi at 60 GHz.

Single End-Fire Antenna for Dual-Beam and Broad Beamwidth Operation at 60 GHz by Artificially Modifying the Permittivity of the Antenna Substrate

A technique is proposed to generate a dual-beam and broad beamwidth radiation in the $E$ -plane of a printed bow-tie antenna operating over 57–64 GHz. This is achieved by artificially modifying the dielectric constant of the antenna substrate using arrays of metamaterial inclusions realized using stub-loaded H-shaped unit cells to provide a high index of refraction. The H-shaped inclusions are tilted with respect to the axis of the antenna and embedded in the direction of the end-fire radiation. The resulting dual-beam radiation in the $E$ -plane has maxima at +60° and 120° with respect to the end-fire direction (90°), with a maximum peak gain of 9 dBi at 60 GHz.

Generation of Dual-Beam Patterns using Particle Swarm Optimization

Certain antenna applications require Dualbeam radiation patterns. The main aim of this paper is to generate the dualbeam radiation patterns from an array of isotropic radiators with single prefixed amplitude distribution. The optimal phase excitations are obtained using Particle Swarm Optimization. Beam 1 is a highly directive pencil beam and beam 2 is a ramp pattern. It is well known that, ramp patterns are generated from waveform generators. Interestingly, an attempt has been made to produce these patterns from radiating elements in the form of farfield radiation pattern. Ramp shape radiation patterns do not exhibit symmetry about the bore sight direction. All the excitation phases are set to 0 to generate pencil beam and are varied in the range of -π to +π to generate ramp pattern. Results obtained for different scan angles are presented.

An efficient directional fast neutron sensor for a mixed radiation field

Abstract Dual beam radiation transmission systems are often used to non-invasively distinguish binary materials in security, industrial and medical applications. Material discrimination is based on detecting changes in hydrogen content and effective atomic number. We propose use of a dual beam technology in the reverse sense, as a sensitive directional sensor for fast neutrons in a mixed radiation field. The system uses retractable filter elements aligned with an organic scintillation detector and displays a distinctive digital-like response. Detected events are processed with a discriminator and basic counting system. We discuss the detection principle, the fast neutron detection threshold, the basic operational algorithm used and the response to different incident radiation energies. We propose work to extend the capabilities. This direction-sensitive detection concept may improve the sensitivity for detecting special nuclear materials such as in stacks of sea containers.

An aperture-coupled linear microstrip leaky-wave antenna array with two-dimensional dual-beam scanning capability

This paper describes an X-band 4/spl times/1 aperture-coupled series-fed electronically steerable microstrip leaky-wave antenna (LWA) array design, which has dual-beam radiation pattern and two-dimensional (2-D) beam-scanning capability. The LWA array is operated in the first higher order mode and excited by center-fed aperture coupled for dual-beam operation. The varactor-tuned phase shifters are placed between the antenna elements. The measured half-power beamwidth of the H-plane and quasi-E-plane radiation patterns are less than 30/spl deg/. By tuning the reverse dc bias of the varactor diodes, the main beam can be scanned in azimuth plane from -13/spl deg/ to +13/spl deg/ off broadside. In the elevation plane, the beam-scanning angle is close to 20/spl deg/ as the operating frequency tuned from 11.58-12.5 GHz. Taking into account each phase-shifter insertion loss and phase progression, the measured results compared closely with the theoretical prediction. The proposed antenna array is suitable for wireless communication and collision warning radar systems.

An aperture-coupled linear leaky-wave antenna array with 2-D dual-beam scanning capability

An X-band four-element linear microstrip leaky-wae () antenna LWA array with a dual-beam radiation pattern and two- dimensional scanning capability is deeloped. The measured half- power beamwidths of the H-plane and quasi-E-plane radiation patterns are less than 308. By tuning the dc bias of thearactor phase shifter between the antenna elements, the main beam can be scanned in the azimuth plane from y138 to q138 off broadside. In the eleation plane, the beam-scanning angle is close to 208 as the operating frequency is tuned from 11.58 to 12.5 GHz. Q 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 25: 52)53, 2000.

A back-to-back dual-beam active microstrip leaky-wave antenna array with mode-switching capability

An X-band two-element back-to-back coupled-oscillatordri en spatial power-combining microstrip leaky-wa e antenna array is de eloped, which has a dual-beam radiation pattern and mode-switching capability. Two Gunn diode CPW oscillators are placed on the back side of the substrate, each dri ing two back-to-back microstrip leaky-wa e antenna pairs in opposite directions for dual-beam operation. This acti e antenna array is able to produce sum and difference patterns between the in-phase and 1808 out-of-phase mode by controlling the bias oltages of the Gunn diodes. Q 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 24: 195]197, 2000.

Back-Face Only Electrical Connections of Thickness Mode Piezoelectric Transducers

The radiation patterns of disk transducers connected in a recently reported novel manner by Laughlin, Drews, and Wilson is studied. In this connection, the back-face plating of a transducer is divided into two electrodes which constitute the only transducer-to- transceiver connection, and a dual-beam radiation pattern resulted. However, we found that repolarizing one half of the transducer re- stored a single beam pattern. This method of connection and regionally repolarizing the piezoelectric transducer appears highly advantageous for use in fabrication of both miniature transducers and various trans- ducer arrays (e.g., linear, annular, and matrix).