Input impedance matching and near field distribution characteristics of unbalanced fed ultra low...

Input impedance matching and near field distribution characteristics of unbalanced fed ultra low profile inverted L antenna

Abstract

The author has proposed the unbalanced fed ultra low profile inverted L antenna on the rectangular conducting plane (ULPIL). This antenna is composed of the semi-rigid coaxial cable. The inner conductor of the coaxial cable is extended from the end of outer conductor, that is, this antenna is excited at the end of outer conductor in the numerical analysis. By adjusting the length of horizontal element and the position of feed point, the input impedance is easily matched to 50 Ohm. When the size of conducting plane is 0.245lambda (lambda: wavelength) by 0.49 lambda and the antenna height is lambda/30, and the length of horizontal element is around lambda/4, the input impedance of this antenna is matched to 50 Ohm and its directivity becomes more than 4 dBi. As a low profile antenna, the base fed inverted F (BFIF) antenna is well known. This antenna is composed of the base fed inverted L antenna and the short-circuited stub for impedance matching.

In this talk, the characteristics of ULPIL antenna are compared with those of the BFIF antenna. The mechanisms of impedance matching of two antennas are discussed by comparing their equivalent circuits.

In ULPIL antenna, the inverted L element and the conducting plane are strongly coupled and the electromagnetic field concentrates within the inverted L element and the ground plane. Therefore high gain antenna may be realized by controlling the near field distribution. When the antenna height becomes shorter, the return loss bandwidth becomes narrower. The authors applied this antenna to the wireless power transmission system. When the distance between transmitting and receiving antennas in WPT system is 10 mm, the power transfer efficiency of 99.2% is obtained at the design frequency of 1 GHz. By adjusting the antenna structure and adding the parasitic element, the high gain planar antenna is realized. In this talk, these two examples are also introduced.

About author

Prof. Mitsuo Taguchi received his B. E. and M. E. degrees from Saga University, Japan in 1975 and 1977, respectively, and a Dr. Eng. Degree from Kyushu University Japan in 1986. From 1977 to 1987, he was a Research Associate at Saga University. From 1987 to 2007, he was an Associate Professor at Nagasaki University. Since 2007, he has been a Professor at Nagasaki University.

In 1996 he was a visiting researcher at the Department of Electrical Engineering at the University of California, Los Angeles. He is a member of IEEE, ACES, the Institute of Electronics, Information and Communication Engineers (IEICE) of Japan and the Institute of Image Information and Television Engineers of Japan. He was a Chair of Technical group of Microwave Simulator in IEICE from 2006 to 2007, IEEE AP-S Fukuoka Chapter Chair from 2007 to 2008, IEICE Kyushu Section Chair in 2013.

His research interests are low profile antennas for mobile communication and the education by using the electromagnetic simulator. He wrote the following books; Portable TV Antenna, in “Antenna Engineering Handbook Fourth Edition”, Chapter 30, edited by J. Volakis, McGraw Hill, 2007, Modern Antenna Engineering (in Japanese), Sogo Denshi Publishing, 2004, Fundamentals of Microwave Simulators (in Japanese), IEICE, 2004, and Computational Electromagnetics (in Japanese), Baifukan Publishing, 2003.