• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.11
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• pp.1161-1169
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• 2003

In this paper, ADE(Axially Displaced Ellipse) Gregorian dual reflector antennas, which are the special form of Gregorian dual reflector antennas, were analyzed. In the procedure of antenna analysis, the aperture field distribution was obtained by using the geometrical optics and their far-field radiation characteristics were analyzed by using the aperture field method. The analysis results such as antenna efficiency, HPBW(Half Power Beam Width), FNBW(First Null Beam Width), and FSL(First Sidelobe Level) were presented as functions of edge taper and size of main reflector and subreflector. From the results in this paper, we could confirm that ADE reflector antennas have the different radiation characteristics from the classical dual reflector antennas.

• Nuclear Engineering and Technology
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• v.56 no.7
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• pp.2633-2640
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• 2024

The purpose of this study was to investigate the effect of the reflector, surface treatment, and length of scintillation crystals on the performance of a time-of-flight and depth-of-interaction (TOF-DOI) PET detector with a dual-ended readout and to determine the best reflector and surface treatment. Various types of crystal arrays with three different reflectors (ESR, BaSO₄, and Toray), three different lateral surface treatments (all-polished (AP), all-roughened (AR), and partially roughened (PR, three sides polished, and one side roughened)), and two different lengths (20 and 15 mm) were fabricated. The highest light collection efficiency and best energy resolution were achieved using a crystal with a diffuse reflector (BaSO₄ for AP and Toray for AR). In contrast, the best coincidence timing resolution (CTR) was achieved using an AR crystal with a specular reflector (ESR). The best DOI resolution was achieved using an AR crystal with BaSO₄. Moreover, the results measured with the 20 mm long crystals were similar to those measured with the 15 mm long crystals. Therefore, we concluded that the dual-ended readout PET detector employing the crystal with AR lateral surface treatment and ESR was a good candidate for TOF-DOI PET because it provided excellent CTR and adequate DOI resolution.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.4
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• pp.451-460
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• 2008

Gregorian offset dual-shaped reflector antennas have been widely used in the satellite communication systems for their high gain and low sidelobe characteristics. However, in this paper, it is designed as the CATR(Compact Antenna Test Range) reflector system, and its near-field characteristics are investigated. The CATR facility needs to provide an uniform plane wave with the minimum amplitude and phase ripple and the low cross polarization to the test region. Therefore, the reflector near-field patterns are calculated and presented with the variations of the aperture power distribution, the feed horn pattern, and the distance from the aperture to the test zone. Also, the offset dual-shaped reflector is fabricated at 30 GHz, and its near-field patterns are measured. The measured results are in good agreement with the calculated results. From theses results, we confirm that the designed offset dual-shaped reflector can be used as the reflector system for the compact antenna test range.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.5
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• pp.237-244
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• 2010

In this paper, the dual parabolic cylindrical reflector systems are analyzed as the reflector system for the CATR(Compact Antenna Test Range) facility. The near-field at the test zone of the CATR is calculated by using the PO(Physical Optics) approximation. The CATR has to provide an uniform plane wave with the minimum amplitude and phase ripple and the low cross polarization. Therefore, in this paper, the near-field pattern are calculated, and the ripple and taper of the field and the cross polarization are investigated with the position of the subreflector and the test region. It is confirmed that the analysis results can be used for the design of the CATR with the dual parabolic cylindrical reflector.

• Journal of Satellite, Information and Communications
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• v.10 no.2
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• pp.34-39
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• 2015

In this paper, a design of an offset Cassegrain antenna is proposed for Ku and Ka dual-band without increasing the antenna size. For Efficiency of computation and implementation, the frequency selectivity surface (FSS) of reflecting the Ka-band signal and passing the Ku-band is provided for the sub-reflector instead of the main reflector. The proposed FSS hyperboloid sub-reflector is the periodic structure of a unit cell comprising octagon metal rings embedded in the multiple layers. The proposed design is verified for 19 GHz and 45 GHz bands by the use of precise electromagneitc-field simulations.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.1
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• pp.46-53
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• 2008

In general, the cassegrain dual offset reflector is used for the satellite communication antenna, but is analyzed as the reflector system for the CPTR(Compact Payload Test Range) facility in here. The near-field at the test zone of the CPTR is obtained by using the physical optics approximation. The CPTR has to provide a uniform plane wave with the minimum amplitude and phase ripple and the low cross polarization. Therefore, in this paper, the near-field pattern are calculated, and the ripple and taper of the field and the cross polarization are investigated with the variation of the reflector geometry and the position of the test region. Especially, the cross polarization of the antenna axis direction which is not found in the satellite reflector antennas is investigated.

• Current Optics and Photonics
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• v.4 no.6
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• pp.461-465
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• 2020

A dual-mode laser terahertz source consisting of two in-line distributed Bragg reflector (DBR) laser diodes (LD) is proposed. It is less susceptible to residual reflections from facets than an in-line dual-mode distributed feedback (DFB) LD. The characteristics of the proposed terahertz source are theoretically investigated using a split-step time-domain simulation. It is shown that terahertz waves of frequencies from 385 GHz to 1725 GHz can be generated by appropriate thermal tuning of two DBR LDs. The dual-mode DBR LD terahertz source exhibits good spectral quality for residual facet reflectivity below 0.02, but facet reflectivity of the in-line dual-mode DFB LD terahertz source should be below 0.002 to provide similar spectral quality.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.26 no.5
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• pp.445-454
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• 2015

In this paper, we propose an optimal design method for a dual reflector antenna(DRA) using the Genetic algorithm. In order to reduce the computational burden during the optimal design, we exploit the iterative physical optics(IPO) to calculate the surface current distribution at each reflector antenna. To improve the accuracy, we consider the shadow effect by the structure and the coupling effect by the multi-reflection based on the iterative MFIE(Magnetic Field Integral Equation). To reduce the number of design variables and generate a smooth surface, we use the Bezier function with the control points, which become the design variables in this paper. We adopt the HPBW(Half Power Beam Width), the FNBW(First Null Beam Width), and the SLL(Side Lobe Level) as the objective or cost functions. To verify the results, we compare them with the those of the commercial tool.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.8
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• pp.1352-1358
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• 2006

In this paper, we have fabricated and tested a broad band bow-tie slot antenna with dual reflector. If we put 1/2 length thin and long slot on a wide metal plate, the slot antenna radiates efficient and strong radio wave as same as 1/2 dipole antenna does. we made with bow-tie form slot which has wider broad band than normal rectangular slot. At first, we made and test a single reflector slot antenna. To enlarge the broad band, we inserted another reflection plate between the slot antenna and reflection plate. After the test, we could have known that the low band(VSWR<2.0) has about $22%(793MHz\sim992MHz)$, high band(VSWR<2.0) has about 61% (1626MHz\sim3064MHz).

• The Journal of the Korea institute of electronic communication sciences
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• v.13 no.2
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• pp.341-348
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• 2018

A WLAN dual band dipole antenna with parasitic elements and a reflector is presented for high gain operation. The parasitic elements are used for practical application and high gain operation of the radiation pattern at the WLAN dual band. The proposed antenna consists of three layers, and has dimensions of $74mm{\times}40 mm{\times}31.4mm$. From the experimental results, the achieved impedance bandwidths were 1035 MHz (2.031-3.066 GHz) and 1119 MHz (5.008-6.127 GHz), respectively. The measured maximum gain at each WLAN band was 6.69 dBi and 7.81 dBi, respectively.