Design, Realization, and Analysis of PIFA for an RFID Mini-Reader

Transcription

1 Deign, Realization, and Analyi of PIFA for an RFID Mini-Reader SUNG-FEI YANG ; TROY-CHI CHIU ; CHIN-CHUNG NIEN Indutrial Technology Reearch Intitute (ITRI) Rm. 5, Bldg. 5, 95, Sec., Chung Hing Rd., Chutung, Hinchu, 3 Taiwan, ROC. ccn@itri.org.tw; TroyChiu@itri.org.tw Abtract: - In thi paper a planar inverted-f antenna (PIFA) deigned to operate at 9 98 MHz i preented. It dimenion are reduced by 3% when a meander tructure i etched onto a conventional PIFA. The meaured return lo of the deigned PIFA at 95 MHz i 3 db and the ground plane and patch lot ize of the PIFA can be modified to obtain the required reonance frequencie in a variety of application. Keyword: - RIFD Reader, Patch antenna, PIFA Introduction Current application require that antenna be mounted on mall ground plane, uch a thoe in handheld communication device. The planar inverted-f antenna (PIFA) ha everal advantage, uch a eae of fabrication, low cot, and a imple tructure. PIFA are commonly ued in mall communication terminal, uch a handheld radio, becaue they have a low profile and can cover popular wirele communication band []. However, ome important limitation prevent the ue of PIFA in a wide range of application; namely, their large volume at low frequencie and narrow bandwidth. Patch antenna are often ued in RFID application. They are compoed of a layered tructure with two parallel conductor eparated by a thin dielectric ubtrate, where the lower conductor act a a ground plane. If the ground plane i not large compared to a wavelength, then the electrical performance will uually differ from that of a finite ground plane. The mot common method of reducing their ize i the ue of variou lot, which i equivalent to increaing the electrical length of the patch [3]. RFID Reader Antenna Deign and Analyi L hape [5]. The layout of a typical PIFA i hown in Fig.. The antenna conit of a ground plane, a rectangular patch element aligned parallel to the ground plane, and a hort-circuit plate. Fig.. The layout of a typical PIFA. It reonant frequency can be etimated uing the formula [6]: c f =, (-) ( L + L ) where c i the peed of light, L and L are the length and width of the radiation element, repectively, and f i the reonant frequency. Another way i to create a table decribing the trend of variation in the reonant frequency [6], a hown in Table. Table. Trend of reonant frequency variation in a typical PIFA.. Theoretical Background PIFA have been tudied extenively becaue of their low profile tructure that can be eaily accommodated into wirele handet []. Their baic tructure evolved from the L antenna. The inverted-l antenna i a variation of the monopole antenna, where the monopole antenna i bent into an PIFA are uually very thin. A a reult, the ground plane mut be longer and larger. The cot can be reduced by building the antenna with an air ubtrate, which can be fabricated by tandard PCB manufacturing procee. ISBN:

2 . Deign of the PIFA Prior to deigning the RFID reader antenna, it i neceary to firt determine the matching at 5 Ω. In thi work, a PIFA wa utilized to deign the RFID reader antenna hown in Fig.. Fig.. An inverted-f antenna. The radiation reitance of a PIFA i twice that of the half-wave patch antenna. The reonant frequency given by the model i accurate when W W =. A hown in Fig. 3 [], when W W < L, the current on the underide of the planar element mainly flow to the open-circuit edge on the long ide of the planar element. However, when W W > L, the current flow to the open-circuit edge on the hort ide of the planar element. By analyzing the urface current, it i poible to derive the effective length of the current flow on the hort-circuit plate and the planar element. When W W =, the reonance i expreed by: L + H = λ, (-) while for W =, it i expreed by: L + W + H = λ. (-3) When < W /W <, the reonant frequency can be expreed a: and: W fr = r f + ( r ) f for (-) L k k W fr r f ( r ) f for L r = W W, k W L = +, (-5) where =, and the reonance for the frequency f i given by Equation (-), while the reonance for the frequency f i given by Equation (-3) [7]. f r Fig. 3. Direction of urface current flow on a planar element due to variation in it ize ratio and the width of the hort-circuit plate. 3 Simulation and Meaurement Fig.. The layout of a typical PIFA. An RFID reader antenna need to function at f = 95 MHz. Therefore, the peed of light, 8 c = 3 m, i ued to find the wavelength in free ( ) pace, λ. The total length L of a microtrip patch antenna i: f = c ( L + L ) c ( L + L ) = f = = 6 95 ( L L ).8( m) A lot i elected to reduce the ize of the patch for the PIFA hown in Fig.. Next, imulate an RFID reader antenna i imulated with 5 Ω. The propoed deign ha a ground plane ize of 5 5 mm, a height of h = mm, a trace width of w = 5 mm, and a thickne of t =. mm, a hown in Fig. 5. Some manufactured example of the RFID reader antenna that we deigned are hown in Fig. 9(a) and (b). ISBN:

3 Fig. 5. The deign of the PIFA. The imulated input return lo, Smith Chart, and the radiation pattern are hown in Fig. 6, 7, and 8, repectively. The return lo of the RFID reader antenna at 95 MHz i db when matched to 5 Ω. The RFID tag antenna matche Z A = 55 j9.8, which i the imulation reult from the Smith Chart. In the 3D volume, the radiation pattern i omni-directional and the maximum gain i. dbi. Fig. 6. The imulated return lo of the PIFA for f c = 95 MHz. (a) (b) Fig. 9. Two example of the UHF band RFID antenna with ground plane ize of (a) 5 5 mm and (b) 5 3 mm. for UHF Reader Module in H35m & P37b PDA The meaured bandwidth wa MHz, over a range from 98 MHz to 93 GHz with a db return lo, a hown in Fig.. For f c = 95 MHz, the meaured return lo of 3 db and the Smith Chart with 3.7 j.5 are hown in Fig. and. Fig. 7. The imulated Smith Chart of the PIFA for f c = 95 MHz. Fig.. The meaured return lo of the PIFA for f c = 95 MHz. Fig. 8. The imulated radiation pattern of the PIFA for f c = 95 MHz. Fig.. The meaured Smith Chart for the PIFA for f c = 95 MHz. ISBN:

4 If the PIFA' ground plane ize need to be modified for ue in a different project, the patch lot ize can be adjuted to obtain the reonant frequency hown in Fig. 9(b). The meaured radiation pattern for the x y plane are hown in Fig. and 3. In the x y plane, the radiation pattern i omni-directional. The maximum gain and average gain are.3 dbi and.9 dbi for 95 MHz and 93 MHz, repectively. Fig.. Radiation pattern of the PIFA with a ground plane ize of 5 3 mm in the y z plane (at 95 Fig.. Radiation pattern of the PIFA with a ground plane ize of 5 3 mm in the x y plane (at 95 Fig. 5. Radiation pattern of the PIFA with a ground plane ize of 5 3 mm in the y z plane (at 95 Fig. 3. Radiation pattern of the PIFA with a ground plane ize of 5 3 mm in the x y plane (at 95 The meaured radiation pattern in the y z plane are hown in Fig. and 5. In the y z plane, the radiation pattern i omni-directional. The maximum gain and average gain are.66 dbi and.88 dbi for 95 MHz and 93 MHz, repectively. Concluion The planar inverted-f antenna (PIFA) i a common choice for ue in portable wirele device, for it mall ize and profile, imple deign, eay fabrication and low cot. However, PIFA are limited from widepread application due to their narrow bandwidth and large volume at low frequencie. The radiation reitance of a PIFA i twice that of a half-wave patch antenna. The reonant frequency determined by the model i accurate W when W =. For f c = 95 MHz, the meaured return lo wa 3 db and the Smith Chart had 3.7 j.5. In the x y plane, the radiation pattern wa omni-directional. The maximum gain and average gain were.77 dbi and.3 dbi for 95 MHz and 95 MHz, repectively. In the y z plane, the radiation pattern wa alo omni-directional. The maximum gain and average gain were.66 dbi and.7 dbi for 95 MHz and 93 MHz, repectively. ISBN:

5 Reference: [] Chia-Yu Lee, Deign of On-Package Planar Inverted-F Antenna for RF ytem-on-package Application, June 5. [] David M. Pozar, Microwave Engineering: Third Edition, John Wiley & Son, INC, 5. [3] Warren L. Stuzman; Gary A. Thiele, Antenna theory and deign, nd edition, John Wiley & Son, INC, 998. [] Lal Chand Godara, Handbook of Antenna in Wirele Communication, Boca Raton London New York Wahington,D.C. pp.-8 -,. [5] Raleigh, G.G., Diggavi, S.N., Jone, V.K., and Paulraj, A., A blind adaptive tranmit antenna algorithm for wirele communication, in Proc. ICC, IEEE, 995,vol.3,9-99. [6] Fang, I. Hu, Planar Near-Field to Far-Far-Field Tranformation and PIFA 5 Antenna Suitable for Wirele LAN, 3-9, June. [7] Kazuhiro Hiraawa and Miao Haneihi, Analyi, deign, and meaurement of mall and low-profile antenna, Artech Houe, INC, 99. ISBN: