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Reaction cross sections (σR) for 24–38Mg on C targets at the energies of around 240 MeV/nucleon have been measured precisely at RIBF, RIKEN for the purpose of obtaining the crucial information on the changes of nuclear structure in unstable nuclei, especially around the so-called “island of inversion” region. In the island of inversion region, which includes neutron-rich Ne, Na, and Mg isotopes, the vanishing of the N = 20 magic number for neutrons have been discussed along with nuclear deformation. The present result suggest deformation features of Mg isotopes and shows a large cross section of weakly-bound nucleus 37Mg, which could be caused by a neutron halo formation.

We report a terahertz metasurface quantum-cascade VECSEL laser without moving parts that can electronically switch between near-orthogonal linearly polarized output. It exhibits excellent beam pattern, single-mode operation, and power up to 93 mW at 77 K.

The feasibility of composite right/left-handed (CRLH) metamaterial waveguides based upon graphene plasmons is demonstrated via numerical simulation. Designs are presented that operate in the terahertz frequency range along with their various dimensions. Dispersion relations, radiative and free-carrier losses, and free-carrier based tunability are characterized. Finally, the radiative characteristics are evaluated, along with its feasibility for use as a leaky-wave antenna. While CRLH waveguides are feasible in the terahertz range, their ultimate utility will require precise nanofabrication, and excellent quality graphene to mitigate free-carrier losses.

A circularly polarized (CP) CRLH-inspired leaky-wave antenna (LWA) based on substrate-integrated waveguide (SIW) and microstrip delay line is presented. The unit-cell of the proposed periodic antenna consists of two conventional CRLH SIW cells and two quarter-wavelength microstrip lines. The interdigital slots on the CRLH SIW are rotated at +45° and -45° with respect to the wave propagation direction and separated by 90° to create circular polarization. Utilizing the microstrip line instead of the SIW delay section, the total size of the five unit-cell antenna is reduced by 24.4% in comparison to the previous single radiator CP LWA. Furthermore, microstrip lines provide improved matching for broadside radiation as well as better CP purity. The unitcell characteristics are investigated in detail through dispersion and Bloch impedance analysis. In addition, space harmonic analysis is carried out to explain the radiation mechanism of the proposed antenna. The proposed CRLH-inspired SIW CP antenna operates from 4.2 to 4.85 GHz and frequency scans from -25° to 26° along the elevation angle. Axial ratio is maintained below 3 dB throughout the operating frequency. The measured results show good agreement with the simulated results.

A planar electromagnetic bandgap (EBG) structure designed for broadband common-mode suppression is proposed. A uniplanar compact photonic-bandgap (UC-PBG) structure with periodic center slots is etched on the ground plane to obtain broadband common mode suppression while minimally disturbing the differential signal within the designed bandwidth. Dispersion analysis has been conducted for both common (even) and differential (odd) mode signals. Good signal integrity is observed in both simulated and measured results. The fractional bandwidth of the proposed EBG ground plane is around 70% with common-mode suppression below - 20 dB. The proposed EBG ground planes may be applicable for systems requiring low-cost and simple solutions in designing high-speed differential interlinks operating above 5 Gbps.

In this letter, a novel dipole antenna based on substrate integrated waveguides (SIWs) is presented. The dipole antenna radiates through the equivalent magnetic current loops on the top and bottom annular ring slot that is excited by the fundamental mode of the SIW cavity. Therefore, the proposed dipole possesses a vertical polarization perpendicular to the metallic plane. Moreover, thanks to normal electric field, the proposed dipole is less affected by the ground plane size and surrounding metal. The proposed antenna topology provides a very easy way to realize vertical dipole antenna by just using planar circuits and is promising to be used as a fundamental element to realize antenna arrays. © 2002-2011 IEEE.

A comprehensive method to synthesize negative group delay (NGD) in the microwave regime with a maximally flat response is proposed in this paper. This method is based on transversal-filter topologies; it will be shown that by choosing proper coupling coefficients of each tap of a transversal filter, we can realize NGDs with maximally flat characteristics at the output of the transversal filter. The desired coefficients to realize maximally flat NGDs with various amount of group delay are analytically derived and tabulated in this paper. Furthermore, the results are verified experimentally through microwave transversal-filter approaches in both passive and active ways using multi-section asymmetric directional couplers and distributed amplifiers. © 1963-2012 IEEE.

Several types of multiplexers based on isolation circuits have been introduced and investigated. Combining method of two filtering circuits (CMTC) is one way to make multiplexers based on isolation circuits. This method fits well for designing contiguous channel triplexers. A triplexer based on CMTC consists of a conventional transmission line (TL) connected to a diplexer and a composite right/left-handed (CRLH) TL connected to a filter. The triplexer based on CMTC has two significant advantages. One is that it is not necessary to modify the design of a stand-alone filter and diplexer and there is freedom in the choice of filtering circuits. In addition, a designer does not need to perform three-dimensional full-wave optimization, because of a simple and straightforward design concept. In this paper, a triplexer prototype having 1, 1.125, and 1.25 GHz center frequencies, is designed and fabricated. The measured results show good agreement with the simulation results. © Cambridge University Press and the European Microwave Association 2014.

In this letter, a novel reconfigurable negative group delay distributed amplifier (NGD-DA) circuit is proposed. This NGD-DA offers a new method to realize negative group delay. By properly choosing the gain coefficient of each tap for the DA, we can synthesize the negative group delay at the reverse port of the DA in the frequency band of interest, while maintaining a flat gain at the forward port; this results in a dual-purpose DA. Moreover, the proposed NGD-DA is reconfigurable; the phase response at the reverse port can be simply controlled by adjusting the tap gain coefficients, and therefore the bandwidth as well as the amount of negative group delay can be manipulated. The proposed active NGD circuit is validated through theoretical explanation and experimental results. © 2013 IEEE.

This paper presents an all-passive phased-array feed network based on composite right/left handed (CRLH) transmission lines (TLs). A CRLH TL enables systematic engineering of the phase response providing phase advance in addition to phase delay. When utilized in a phased-array feed network, an all-passive 1-D frequency-scanning array can be designed with a large scanning angle range toward both positive and negative elevation angles. This unique feature cannot be realized using conventional delay lines or dispersive lines that do not contain left-handed properties. Also, unlike the previously studied CRLH-based leaky-wave antennas that provide similar 1-D continuous frequency-scanning functionality, the proposed method completely decouples the radiating antenna element from the array factor; thereby providing extra design freedom and enhanced radiation performance. To validate the added advantage, we use the proposed CRLH-based phased-array feed network to demonstrate simultaneous controllability of the radiated polarization and array current amplitude distribution. © 1963-2012 IEEE.

Prism coupling and reflection spectroscopy are used to characterize bound modes within composite right/left handed terahertz metamaterial waveguides. The cavity antenna model is used to understand the polarization dependence of the radiative coupling to TM00 and TM01 waveguide modes. Furthermore, the cavity model along with transmission-line theory is used to derive a surface impedance model for a waveguide array metasurface. Qualitative agreement with the experiment is observed, including a mode splitting for p-polarized surface waves at the light line and the existence of s-polarized magnetic spoof surface plasmons. © 2013 American Institute of Physics.

We report the demonstration of a composite right/left-handed (CRLH) metamaterial waveguide for terahertz quantum-cascade (QC) lasers. By incorporating gap capacitors (∼ 250 nm) in the top metallization of a metal-metal waveguide operating in a higher order lateral mode, we have realized a CRLH transmission line that supports traveling modes with negative effective phase indices (i.e., left-handed or backward-wave propagation). The CRLH metamaterial waveguide is employed as an active leaky-wave antenna for a terahertz QC-laser. Directional single-lobed beams launched in the backwards direction at angles of - 4 ° and - 63 ° were experimentally observed at excitation frequencies 2.59 and 2.48 THz, respectively. © 2013 American Institute of Physics.

A retrodirective array (RDA) capable of retransmitting predictable polarization with respect to any received polarization state is presented. RDAs have the unique ability to scatter the received signal back to the interrogator without prior knowledge of the source location. In addition to this unique feature, the proposed system can receive any polarization and always retransmits the signal that is orthogonally polarized with respect to the received polarization state. This added feature helps to maintain a more stable communication link between the RDA and the interrogator by mitigating the polarization mismatch loss. The proposed system shows excellent retrodirectivity for various received linear and circular polarizations. © 2013 IEEE.

We report terahertz metamaterial waveguides based on the concept of composite right/left-handed transmission-lines. The waveguides are implemented in a metal-insulator-metal geometry fabricated with spin-coated Benzocyclobutene and contact photolithography. Angle-resolved reflection spectroscopy shows strong resonant absorption features corresponding to both right-handed and left-handed (backward wave) propagating modes within the leaky-wave bandwidth. Tuning of the waveguide dispersion is achieved by varying the effective lumped element series capacitance. The experimental results are in good agreement with full-wave finite element method simulations as well as an intuitive transmission-line circuit model. © 2012 American Institute of Physics.