Summary
International Symposium on Antennas and Propagation
2010
Session Number:4FA2
Session:
Number:4FA2-3
Ultra Low Profile Inverted L Antenna for 2.45 GHz RFID Reader
Mitsuo Taguchi, Tetsuya Yamashita,
pp.-
Publication Date:2010/11/23
Online ISSN:2188-5079
Summary:
The input resistance of a horizontal dipole located very close to a perfect electric conducting plane becomes low due to the existence of a metallic structure, and it approaches zero as the distance is decreased toward zero [1 - 3]. An "ultra low profile dipole (ULPD) antenna", which is a dipole very closely located to a conducting plane, was proposed to solve the impedance matching issue [4]. A half wavelength dipole is excited at the offset points from the center, so that the reasonable impedance can be obtained even with a conducting plane in proximity to the dipole. The maximum gain of 8.4 dBi, which is higher than that of a half-wave dipole on the reflector with a quarter wavelength distance between the dipole and the reflector, is obtained. The return loss bandwidth less than 10 dB is about 2%. The authors proposed an ultra low profile inverted L antenna on a finite conducting plane [5]. This antenna consists of a 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. The antenna height is around one thirtieth of wavelength. The length of horizontal element of this antenna is around a quarter wavelength. By controlling the current on the conducting plane, the gain and the return loss bandwidth are adjustable. In the case of the size of conducting plane is 0.245 λ (λ: the wavelength at the design frequency ) by 0.408 λ, the maximum gain becomes 4.14 dBi and the return loss bandwidth less than 10 dB becomes 2.7 %. For the RFID handheld reader, the low profile, circular polarized antenna is desired. The authors reported the circularly polarized microstrip antenna for the UHF and 2.45 GHz band [6]. The operating frequencies are from 2.4 GHz to 2.4835 GHz for the 2.45GHz band, that is, the bandwidth becomes 83.5 MHz. However, the return loss bandwidth and the axial ratio bandwidth of proposed antenna are 27 MHz and 8 MHz, respectively [6]. The authors also proposed the circular polarized antenna composed of two ultra low profile inverted L elements on the rectangular conducting plane of size 85.6 mm by 100 mm [7]. In this paper, this antenna is miniaturized and measured. In the numerical analysis, the electromagnetic simulator "WIPL-D" based on the method of moment is used [8].