• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.10
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• pp.985-995
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• 2003

In this paper, a study on optimization of three dimensional multi-layered metallic disk array structure(MDAS) excited by circular waveguides was performed to shape efficient flat-topped element patterns(FTEP) of ${\pm}$20$^{\circ}$ beam width. Each radiating element of the MDAS is composed of input, transition and radiation circular waveguides and finite metal disks stacked on radiation circular waveguide. It has an array structure of a hexagonal lattice appropriate for the conical beam scanning. The analytic algorithm for the MDAS was proposed and the code was also programmed using it. Optimal design parameters of the MDAS were determined through the optimal simulation process to obtain ${\pm}$20$^{\circ}$ FTEP. Also, bandwidth characteristics for FTEP and reflection coefficients of the MDAS were investigated and, as the results, it was shown that the MDAS could shape good FTEPs of ${\pm}$20$^{\circ}$ beam width in main planes at least within a 5.6 % frequency band.

• Progress in Medical Physics
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• v.15 no.1
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• pp.17-22
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• 2004

Multileaf collimator (MLC) is now rapidly replacing the lead ahoy block to shape the radiation treatment field. In addition to its defect of rectangular field shaping and increased penumbra width, it has another possible problem, and that is of radiation transmission between leaves, which needs to be maintained at as low a level as is permissible. The authors measured and analyzed the inter-leaf and cross-leaf transmissions of MLC by Varian Associates Inc, before its clinical application. The inter-leaf and cross-leaf transmissions were calculated by comparing the measured point doses in the polystyrene phantom in the open field and in a total closure of MLC. The beam profile of the inter-leaf and cross-leaf transmissions were depicted by using a water phantom. A photon beam of 6 MV was used in the measurement. The inter-leaf transmission was 1.63∼1.67%, indicating that the shielding effect of MLC is excellent. However, the cross-leaf transmission in the central area was 18.4∼18.7% and this is well over the clinically acceptable limitation of 5%. The beam profile of cross-leaf transmission displayed 80∼90% transmission near the field edge, so that the cross-leaf transmission was 14∼17% in this area. The multileaf collimator has an excellent shi디ding effect and the inter-leaf transmission is negligible so that it can be used in clinic as a good replacement of the conventional lead alloy block. However, care must be taken to avoid the cross-leaf transmission in the radiation field.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.13 no.7
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• pp.667-678
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• 2002

In this paper, a new radiating structure with a multi-layered two-dimensional metallic disk array was proposed for shaping the flat-topped element pattern. It is an infinite periodic planar array structure with metallic disks finitely stacked above the radiating circular waveguide apertures. The theoretical analysis was in detail performed using rigid full-wave analysis, and was based on modal representations for the fields in the partial regions of the array structure and for the currents on the metallic disks. The final system of linear algebraic equations was derived using the orthogonal property of vector wave functions, mode-matching method, boundary conditions and Galerkin's method, and also their unknown modal coefficients needed for calculation of the array characteristics were determined by Gauss elimination method. The application of the algorithm was demonstrated in an array design for shaping the flat-topped element patterns of $\pm$20$^{\circ}$ beam width in Ka-band. The optimal design parameters normalized by a wavelength for general applications are presented, which are obtained through optimization process on the basis of simulation and design experience. A Ka-band experimental breadboard with symmetric nineteen elements was fabricated to compare simulation results with experimental results. The metallic disks array structure stacked above the radiating circular waveguide apertures was realized using ion-beam deposition method on thin polymer films. It was shown that the calculated and measured element patterns of the breadboard were in very close agreement within the beam scanning range. The result analysis for side lobe and grating lobe was done, and also a blindness phenomenon was discussed, which may cause by multi-layered metallic disk structure at the broadside. Input VSWR of the breadboard was less than 1.14, and its gains measured at 29.0 GHz. 29.5 GHz and 30 GHz were 10.2 dB, 10.0 dB and 10.7 dB, respectively. The experimental and simulation results showed that the proposed multi-layered metallic disk array structure could shape the efficient flat-topped element pattern.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.3 s.118
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• pp.323-333
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• 2007

In this paper, a new MDAS-DR antenna structure designed to efficiently shape a flat-topped radiation pattern is proposed. The antenna structure is composed of a stacked micro-strip patch exciter and a multi-layered disk array structure(MDAS) surrounded by a dielectric ring. The MDAS, which was supplied by a stacked microstrip patch exciter with radiating power, can form a flat-topped radiation pattern in a far field by a mutual interaction with the surrounding dielectric ring. Therefore, the design parameters of the dielectric ring and the MDAS structure are important design parameters for shaping a flat-topped radiation pattern. The proposed antenna used twelve multi-layered disk array elements and a Teflon material with a dielectric constant of 2.05. An antenna operated at 10 GHz$(9.6\sim10.4\;GHz)$ was designed in order to verify the effectiveness of the proposed antenna structure. The commercial simulator of CST Microwave $Studio^{TM}$, which was adapted to a 3-D antenna structure analysis, was used for the simulation. The antenna breadboard was also fabricated and its electrical performance was measured in an anechoic antenna chamber. The measured results of the antenna breadboard with a flat-topped radiation pattern were found to be in good agreement with the simulated one. The MDAS-DR antenna gain measured at 10 GHz was 11.18 dBi, and the MDAS-DR antenna was capable of shaping a good flat-topped radiation pattern with a beam-width of about $40^{\circ}$, at least within a fractional bandwidth of 8.0 %.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.12
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• pp.1340-1350
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• 2009

The design and implementation of planar Active Phased Array Antenna System are described in this paper. This Antenna system operates at X-band with its bandwidth 10 % and dual polarization is realized using dual slot feeding microstrip patch antenna and SPDT(Single Pole Double Through) switch. Array Structure is $16\times16$ triangular lattice structure and each array is composed of TR(Transmit & Receive) module with more than 40 dBm power. Each TR module includes digital attenuator and phase shifter so that antenna beam can be electronically steered over a scan angle$({\pm}60^{\circ})$. Measurement of antenna pattern is conducted using a near field chamber and the results coincide with the expected beam pattern. From these results, it can be convinced that this antenna can be used with control of beam steering and beam shaping.

• Radiation Oncology Journal
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• v.11 no.2
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• pp.439-448
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• 1993

The B-type gamma knife unit was installed at Kyung-Hee University Hospital in March 1992. The selective beam plugging method can be used to reduce the low percentage isodose profiles of normal sensitive organ and to modify the isodose curves of treatment volume for better shaping of the target volume. For representing the changes of the low percentage isodose profiles, the variations of dose distribution for several cases were discussed in this paper. The film dosimetry was peformed for the evaluation of calculated isodose profiles predicted by KULA dose planning system. The results were verified by RFA-3 automatic densitometry. The clinical application of selective beam shielding method was peformed in 17 patients in 100 patients who have undergone gamma knife radiosurgery for a year. The calculated and the measured isodose profiles for the high percentage regions were well consistent with each other. When the target of pituitary tumor is macro-size, the selective beam shielding method is the most applicable method. When the target size, however, is small, the correct selection of the proper helmet size is very important. All patients were exposed almost about 3~12 Gy for brain stem, and 3~11.2 Gy for optic apparatus. It is recommended that the same or other plugging patterns with multiple isocenters should be used for protection of the radiosensitive normal structures with precise treatment of CNS lesions.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.12
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• pp.1380-1393
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• 2010

This paper presents a design, fabrication and the test results of planar active electronically scanned array(AESA) radar prototype for airborne fighter applications using transmit/receive(T/R) module hybrid technology. LIG Nex1 developed a AESA radar prototype to obtain key technologies for airborne fighter's radar. The AESA radar prototype consists of a radiating array, T/R modules, a RF manifold, distributed power supplies, beam controllers, compact receivers with ADC(Analog-to-Digital Converter), a liquid-cooling unit, and an appropriate structure. The AESA antenna has a 590 mm-diameter, active-element area capable of containing 536 T/R modules. Each module is located to provide a triangle grid with $14.7\;mm{\times}19.5\;mm$ spacing among T/R modules. The array dissipates 1,554 watts, with a DC input of 2,310 watts when operated at the maximum transmit duty factor. The AESA radar prototype was tested on near-field chamber and the results become equal in expected beam pattern, providing the accurate and flexible control of antenna beam steering and beam shaping.

• Journal of Radiation Protection and Research
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• v.39 no.2
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• pp.81-88
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• 2014

Recently, a new imaging method, gamma vertex imaging (GVI), was proposed for the verification of in-vivo proton dose distribution. In GVI, the vertices of prompt gammas generated by proton induced nuclear interaction were determined by tracking the Compton-recoiled electrons. The GVI system is composed of a beryllium electron converter for converting gamma to electron, two double-sided silicon strip detectors (DSSDs) for the electron tracking, and a scintillation detector for the energy determination of the electron. In the present study, the modules of a charge sensitive preamplifier (CSP) and a shaping amplifier for the analog signal processing of DSSD were developed and the performances were evaluated by comparing the energy resolutions with those of the commercial products. Based on the results, it was confirmed that the energy resolution of the developed CSP module was a little lower than that of the CR-113 (Cremat, Inc., MA), and the resolution of the shaping amplifier was similar to that of the CR-200 (Cremat, Inc., MA). The value of $V_{rms}$ representing the magnitude of noise of the developed system was estimated as 6.48 keV and it was confirmed that the trajectory of the electron can be measured by the developed system considering the minimum energy deposition ( > ~51 keV) of Compton-recoiled electron in 145-${\mu}m$-thick DSSD.

• Progress in Medical Physics
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• v.5 no.1
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• pp.87-99
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• 1994

Purpose : The determination of electron beam output factor was investigated from individual applicator for various energy of ML-15MDX linear accelerator. The output factor of electron beam was extended from square to rectangular field in individual applicator size through with a least-square fit to a polynomial expression. Materials : In this experiments. the measurement of output was obtained from 2${\times}$cm$^2$ to 20${\times}$20cm$^2$ of field size in different applicator size for 4 to 15 MaV electron beam energy. The output factor was defined as the ratio of maximum dose output on the central axis of the field of individual applicator size to that of a given field size. Applicator factors were derived from comparing with the output dose of reference field size 10${\times}$10cm$^2$. The thickness of block was specially designed as 10mm in thickness of Lipowitz metal for field shaping in all electron energy. Two types of output curves are included as output factors versus side of square fields and that of variable side length for X and Y in one-dimensional to compare the expected values to that of experiments. Results : Expected output factors of rectangular which was derived from that of square fields in individual applicator size from 2${\times}$2cm$^2$ to 20${\times}$20cm$^2$ in different electron energy was very closed to that of experimental measurements within 2% uncertainty. However 1D method showed a 3% discrepancy in small rectangular field for low energy electron beam. Conclusion : Emperical non-linear polynomial regressions of square root and 1D method were performed to determin the output factor in various field size and electron energy. The expected output of electron beam of square root method for square field and 1D method for rectangular field were very closed to that of measurement in all selected electron beam energy.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.1 s.116
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• pp.62-75
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• 2007

This paper describes a shaped-beam antenna for increasing the antenna gain of a radiating element. The proposed antenna structure is composed of an exciting element and a multi-layered disk array structure(MDAS). The stack micro-strip patch elements were used as the exciter for effectively radiating the electromagnetic power to the MDAS over the broadband, and finite metallic disk array elements - which give the role of a director for shaping the antenna beam with the high gain - were finitely and periodically layered onto it. The efficient power coupling between the exciter and the MDAS should be carried out in such a way that the proposed antenna has a high gain characteristic. The design parameters of the exciter and the MDAS should be optimized together to meet the required specifications to meet the required specifications. In this study, a shaped-beam antenna with high gain was optimally designed under the operating conditions with a linear polarization and the frequency band of $9.6{\sim}10.4\;GHz$. Two methods constructed using thin dielectric film and dielectric foam materials respectively were also proposed in order to implement the MBAS of the antenna. In particular, through the computer simulation process, the electrical performance variations of the antenna with the MDAS realized by the thin dielectric film materials were shown according to the number of disk array elements in the stack layer. Two kinds of antenna breadboard with the MDAS realized with the thin dielectric film and dielectric foam materials were fabricated, but experimentation was conducted only on the antenna breadboard(Type 1) with the MDAS realized with the thin dielectric film materials according to the number of disk array elements in the stack layer in order to compare it with the electrical performance variations obtained during the simulation. The measured antenna gain performance was found to be in good agreement with the simulated one, and showed the periodicity of the antenna gain variations according to the stack layer number of the disk array elements. The electrical performance of the Type 1 antenna was measured at the center frequency of 10 GHz. As the disk away elements became the ten stacks, a maximum antenna gain of 15.65 dBi was obtained, and the measured return loss was not less than 11.4 dB within the operating band. Therefore, a 5 dB gain improvement of the Type 1 antenna can be obtained by the MDAS that is excited by the stack microstrip patch elements. As the disk array elements became the twelve stacks, the antenna gain of the Type 1 was measured to be 1.35 dB more than the antenna gain of the Type 2 by the outer dielectric ring effect, and the 3 dB beam widths measured from the two antenna breadboards were about $28^{\circ}$ and $36^{\circ}$ respectively.