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The self-complementary antenna (SCA) is a basic antenna for extremely broadband practical antennas.〔D. E. Isbell, “Log-periodic dipole arrays” ''IRE Trans. Antennas Propag.'', vol. AP-8, pp.260-267, May 1960.〕〔R. L. Carrel, “The design of log-periodic dipole antennas,” ''IRE Intl. Conv. Rec., pt. 1'', pp. 61-75, 1961〕〔Y. Mushiake, Log-periodic structure provides no broad-band property for antennas. ''J. IECE Japan'', 82, No 5, pp. 510-511, May 1999. (in Japanese)〕〔Y. Mushiake, “A report on Japanese developments of antennas: From the Yagi-Uda antenna to self-complementary antennas”, ''IEEE Ant. Prop. Magazine'', Vol. 46, No. 4, pp. 47-60, August 2004〕 This antenna〔S. Uda, and Y. Mushiake, “The input impedances of slit antennas,” ''Tech. Rep. of Tohoku Univ.'', 14, 1, September 1949. pp. 46-59.〕 is an arbitrarily shaped antenna which is constituted with a half of an infinitely extended planar-sheet conductor such that the shape of its complementary structure is exactly identical, or "self-complementary" with that of the original structure with two terminals for the simplest case. The self-complementary antenna has constant input impedance〔Y. Mushiake, “The input impedances of slit antennas,” ''J. IEE Japan'', 69, 3, March 1949. pp. 87-88. (in Japanese)〕〔Y. Mushiake, “Constant-impedance antennas," ''J. IECE Japan'', 48, 4, April 1965. pp. 580-584. (in Japanese)〕 independent of the source frequency and the shape of the structure. Examples for two shapes of the structures are shown in the attached figures. The structures 1 to 3 are for square shape,〔T. Furuya, T. Ishizone,and Y. Mushiake, “Alternate-leaved Self-complementary Antenna and Its Application to High Gain Broadband Antenna”, ''IECE (presently IEICE), A・P, 77-43'', 1977, pp. 35-40. (in Japanese)〕 and the structures 4 to 6 are spiral shape. Actually, the structures extend infinitely, but the figures show only finite portions near the feed point of each structure. File:rot.sca.0.gif|Explanation of SCA structure 1 File:Anima.rotsca.gif|Explanation of SCA structure.2 File:rot.sca.blue.gif|Explanation of SCA structure.3 File:spiral.sca.1.gif|Explanation of SCA structure.4 File:Anima.spiral.sca.gif|Explanation of SCA structure.5 File:spiral.sca.6.gif|Explanation of SCA structure.6 The type of the self-complementary antenna is not limited only to the case of a planar antenna with two terminals, but there are ( more general types ) of structures with various grades of complexity and infinite freedom in their structures, such as, the number of terminals, the number of reference planes, and others. They also have constant-impedance property independent of the source frequency and the shape of the structure for respective classes of structures with various grades of complexity. This general principle of self-complementarity is also called the "Mushiake Principle" by various sources. The equation which gives the constant value of the input impedance for self-complementary antenna is called the "Mushiake Relationship". The values of the constant-impedance for various classes of complexity in the self-complementary structures depend on the respective grades of the complexity. For example, the Mushiake relationship for the simplest self-complementary planar antenna with two terminals is expressed as: Z = Z0/2≒188.4 (), (Mushiake relationship) where Z is the input impedance of the antenna, and Z0 is the intrinsic impedance of the medium. Moreover, experimental studies on self-complementary antennas, including radiation properties, are conducted in Japan. As the results of the experiment, it is found that the truncated alternate-leaves type self-complementary antenna (or Square SCA) has (practically omnidirectional radiation pattern ) as well as the broadband property. These really beneficial characteristics are certainly worthy of attention. == Comparison with log-periodic antennas == The so-called log-periodic antenna is actually a modified〔folded up〕 square self-complementary antenna with log-periodic shape, and the original structure before its modification has a typical self-complementary shape. The log-periodic shape does not provide the broadband property for antennas.〔Y. Mushiake, “Constant-impedance antennas," ''J. IECE Japan'', 48, 4, pp. 580-584, April 1965〕 This fact is (experimentally proven ). It is also evident from the IEEE definition of “Log-Periodic Antenna”.〔“''Log-periodic antenna'' Any one of a class of antennas having a structural geometry such that its impedance and radiation characteristics repeat periodically as the logarithm of frequency.” (see Acknowledgments, and footnote in page 1), ''Self-Complementary Antennas―Principle of Self-Complementarity for Constant Impedance''―, by Y. Mushiake, Springer-Verlag London Ltd., London, 1996〕 The "Log-Periodic Dipole Array"〔 or "Log-Periodic Dipole Antenna"〔R. L. Carrel, “The design of log-periodic dipole antennas,” ''IRE Intl. Conv. Rec., pt.Ⅰ'', pp. 61-75, 1961〕 (LPDA), is a practically modified self-complementary antenna. LPDA has transposed excitation for the dipole array resulted from (folding up ) the antenna structure to obtain unidirectional radiation, that is inevitable outcome of the modification. Moreover, it is pointed out that the log-periodic structure failed to provide constant-impedance property for antennas over one period. However, one certain way to eliminate such variation is to make the shape self-complementary,〔V. H. Rumsey, ''Frequency independent antennas'', Academic Press, New York and London. 1966. (27, 29, 30, 55 )〕 and the expression for the constant impedance is called “Mushiake’s relation”. Accordingly, LPDA is actually a Modified Self-complementary Dipole Array (MSCDA) with log-periodic shape. Where the self-complementary shape has infinite freedom and further evolution is expected for this type of broadband dipole array. Incidentally, with recent widespread of Wi-Fi utilization, this type of broadband Dipole Array (( MSCDA )) has become more important. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Self-complementary antenna」の詳細全文を読む スポンサード リンク
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