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- 저자 : Mittra (검색결과 5 건)
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Application of Transformation Electromagnetics to Cloak Design and Reduction of Radar Cross Section
Raj Mittra,Yuda Zhou 한국전자파학회JEES 2013 Journal of Electromagnetic Engineering and Science Vol.13 No.2
In this paper we present an alternative approach to addressing the problem of designing cloaks for radar targets, which have been dealt with in the past by using the transformation optics (TO) algorithm. The present design utilizes realistic materials, which can be fabricated in the laboratory, and are wideband as well as relatively insensitive to polarization and incident angle of the incoming wave. The design strategy, presented herein, circumvents the need to use metamaterials for cloak designs that are inherently narrowband, dispersive and highly sensitive to polarization and incident angle. A new interpretation of the TO algorithm is presented and is employed for the design of radar cross section-reducing absorbers for arbitrary targets, and not just for canonical shapes, e.g., cylinders. The topic of performance enhancement of the absorbers by using graphene materials and embedded frequency structure surfaces is briefly mentioned. The design procedure for planar absorbing covers is presented and their performance as wrappers of general objects is discussed. A number of test cases are included as examples to illustrate the application of the proposed design methodology, which is a modification of the classical TO paradigm.
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Design of frequency selective surface superstrates for scanning microstrip patch array antenna
Hyun Lee, Dong,Mittra, Raj,Sang Park, Wee Wiley Subscription Services, Inc., A Wiley Company 2007 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS Vol.49 No.12
<P>We investigate the directivity, sidelobe level (SLL) and maximum radiation angle characteristics of a frequency selective surface (FSS) superstrate placed above a 5 × 1 patch array antenna for different scan angles. We find that the frequency at which a high directivity is achieved moves higher as the scan angle of the array is increased, and that the size of the original FSS superstrate needs to be increased along the direction of the scan angle, in comparison to that of the broadside case (0°), to effectively enhance the directivity and suppress the SLL. A rectangular FSS superstrate with enlarged dimension in the scan direction is proposed, and the radiation patterns of the original and elongated FSS composites are compared. For a 20° scan angle of the array antenna, the directivity and the SLL of the changed FSS composite are enhanced by 1.3 and 3.9 dB, respectively, relative to those of the original FSS composite. We compare and summarize the results for the directivity and SLL characteristics of four different antenna prototypes, namely a single antenna; a conventional 5 × 1 array antenna; the FSS antenna composite with a single patch antenna; and an FSS array composite comprising of a 5 × 1 array antenna designed for a scan angle of 0°. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 3184–3187, 2007; Published online in Wiley InterScience (www.interscience.wiley.com).DOI 10.1002/mop.22919</P>
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Modified Wilkinson power divider for suppression of nth harmonics
Kim, M. G.,Kim, J. S.,Mittra, R. IET 2012 Electronics letters Vol.48 No.24
<P>A modified network to suppress the <I>n</I>th harmonics in a Wilkinson power divider is presented. The solution has been found by adding transmission lines, whose electrical lengths are determined by using the suppression terms, between two transformers of the traditional design. Experimental results show that the second and third harmonics levels achieved are -45.3 and -46.4 dB, respectively, while the performance of the power divider at the fundamental frequency is maintained.</P>
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Lee, Dong Hyun,Lee, Young Ju,Yeo, Junho,Mittra, Raj,Park, Wee Sang Wiley Subscription Services, Inc., A Wiley Company 2007 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS - Vol.49 No.1
<P>In this letter, a ring-shaped frequency selective surface (FSS) superstrate is designed to enhance the directivity of a circularly polarized patch antenna by reducing the sidelobe levels. Based on the unit cell simulation, several important parameters that characterize the ring-shaped FSS superstrate are investigated, and the design procedure of the FSS superstrate is described. The FSS antenna composite is fabricated, and the maximum directivity is 18.98 dBi, while the sidelobe level is −18 dB. Furthermore, the antenna composite maintains its circular polarization characteristic quite well. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 199–201, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22084</P>
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이중 대역 지향성 증가용 박판 주파수 선택적 표면의 설계
이동현,이영주,여준호,박위상,Lee Dong-Hyun,Lee Young-Ju,Yeo Jun-Ho,Mittra Raj,Park Wee-Sang 한국전자파학회 2006 한국전자파학회논문지 Vol.17 No.7
We propose a thin frequency selective surface(FSS) superstrate etched on a substrate for dual-band directivity enhancement, and present a design method of the superstrate. In the proposed new design, two FSS arrays with the same periodicity, but with different alignments are placed above and below a thin dielectric layer to overcome the problem of conventional superstrates for dual band directivity enhancements. Based on the unit-cell simulation, several important parameters that characterize the thin FSS superstrate are investigated, and the procedure for designing such a superstrate is described. We compare the resonant frequencies and the qualify factors of the unit cell with those of three FSS antenna composites with different quality factors, and identify the quality factors which support similar directivity enhancement at the dual-band directivity enhancement. It was found that there is an optimum FSS array size of a superstrate to enhance the directivity most efficiently. Measured results for a fabricated superstrate show a good agreement with the simulated ones. 본 논문에서는 하나의 유전체 층으로 이중 대역 지향성을 증가시킬 수 있는 박판 frequency selective surface (FSS) superstrate를 제안하고 이의 설계 방법을 소개하였다. 제안하는 박판 FSS superstrate는 동일한 주기의 두 FSS 어레이가 하나의 유전층 위 아래로 존재하고, 두 FSS 어레이의 위치에 offset 을 주어 이중 대역 지향성 향상을 위한 기존의 FSS superstrate가 가지는 문제점을 제거하였다. 단위 셀 시뮬레이션을 이용하여 다양한 파라미터의 변화에 따른 특성을 분석하고, 이를 이용하여 제안하는 superstrate의 설계 방법을 제시하였다. 3 가지 다른 quality factor를 가지는 단위 셀과 이를 이용한 복합 안테나의 특성을 비교하여 두 대역에서의 지향성 향상 정도를 유사하게 하는 단위 셀의 quality factor 값을 제시하였다. 이와 함께 효율적으로 지향성을 향상시킬 수 있는 최적의 FSS 어레이 크기를 제시하였다. 제안한 박판 FSS superstrate를 이용한 안테나 복합체를 제작하였으며, 측정된 결과는 시뮬레이션 된 결과와 매우 잘 일치한다.
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