Low-Cost Flat Metal-Plate Dipole Antenna for 2.4/5 GHz WLAN Operation

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A low-cost, one-piece, flat-plate dipole antenna for dual WLAN band operation is presented. The dipole antenna is rectangular in shape with the dimensions 10 mm × 37 mm and fed by 50-ohm mini-coaxial cable. By cutting two L-shaped slits in each radiating arm, two dipole arms are obtained, which form a larger dipole and a smaller dipole antennas for the 2.4 and 5 GHz band operation respectively. The dipole arms are further short-circuited, making it possible for the antenna to be fabricated by stamping a single, flat metal plate only. The impedance bandwidth for 2.4/5 GHz WLAN operation is with VSWR below 1.5 and good omnidirectional radiation patterns are also observed.

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Low-Cost Flat Metal-Plate Dipole Antenna for 2.4/5 GHz WLAN Operation

  1. 1. LOW-COST FLAT METAL-PLATE DIPOLE ANTENNA FOR 2.4/5-GHZ WLAN OPERATION Saou-Wen Su and Jui-Hung Chou Technology Research Development Center, Lite-On Technology Corporation, Taipei 11492, Taiwan; Corresponding author: susw@ms96.url.com.tw Received 2 November 2007 ABSTRACT: A low-cost, one-piece, flat-plate dipole antenna for dual WLAN band operation is presented. The dipole antenna is rectangular in shape with the dimensions 10 mm 37 mm and fed by 50- mini- coaxial cable. By cutting two L-shaped slits in each radiating arm, two dipole arms are obtained, which form a larger dipole and a smaller dipole antennas for the 2.4- and 5-GHz band operation, respectively. The dipole arms are further short-circuited, making it possible for the antenna to be fabricated by stamping a single, flat metal plate only. The impedance bandwidth for 2.4/5-GHz WLAN operation is with VSWR below 1.5 and good omnidirectional radiation patterns are also observed. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1686 –1687, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23461 Key words: antennas; planar antennas; dipole antennas; metal-plate antennas; WLAN antennas 1. INTRODUCTION Coaxial-line-fed, mobile-unit antennas of a small form factor [1-7] are very attractive to WLAN applications in many sorts of wireless electronics devices such as laptops and audio/video adapters. Most of them are in the form of printed antenna structures [1-5] in either monopole [1-3] or dipole antenna [4, 5] designs. As to metal-plate structures, Planar inverted-F Antennas (PIFAs) [6, 7] are com- monly utilized in industry as standard antenna solutions. More- over, small mobile-unit antennas in metal-plate structures have better antenna gain and radiation efficiency, and also less costly than printed antennas. However, in general, these kinds of mobile- unit, metal-plate PIFAs cannot provide good omnidirectional ra- diation patterns compared with dipole antennas. In this letter, we demonstrate a one-piece, flat, metal-plate dipole antenna for dual-band WLAN operation in the 2.4-GHz Figure 1 (a) Geometry of the proposed low-cost flat metal-plate dipole (2400 –2484 MHz) and 5-GHz [5.2 GHz (5150 –5350)/5.8 GHz antenna. (b) Photograph of a working sample fed by a 50- mini-coaxial (5725–5825 MHz)] bands. The proposed antenna retains the merit cable. [Color figure can be viewed in the online issue, which is available at of the aforementioned, mobile-unit, flat-plate PIFAs and yet has www.interscience.wiley.com] better omnidirectional radiation characteristics. The antenna com- prises two radiating arms and a shorting strip, short-circuiting both radiating arms, which form a one-piece, flat, metal-plate structure. Two L-shaped slits, in the opposite direction, are further cut in stamping a one-piece, flat metal plate at low cost. Photograph of a each of the two radiating arms to achieve two separate resonant working sample, made of a 0.3-mm-thick copper–nickel–zinc al- paths for dual band operation. The proposed antenna is very suited loy, is shown in Figure 1(b). to be installed within the housing of wireless electronics devices In the proposed design, two L-shaped slits, in the opposite and ideal for integration into WLAN applications. direction, are cut in each radiating arm [detailed dimensions are given in Fig. 1(a)]. When there are no L-shaped slits, the two 2. ANTENNA DESIGN radiating arms form a simple, planar dipole antenna, operating at Figure 1(a) shows the configuration of the proposed antenna. The about 3.15 GHz. With the presence of the L-shaped slits, two new antenna comprises two radiating arms and a narrow shorting strip dipole arms are obtained, which form a larger dipole and a smaller that connects both radiating arms. The antenna is rectangular in dipole antennas for operation in the 2.4- and 5-GHz bands, respec- shape with the dimensions 10 mm 37 mm and fed by 50- tively. Note that the distance (d) between the points A, B, and the mini-coaxial cable, with central conductor connected to the point shorting strip has a major effect on the impedance matching, which A and the outer sheath soldered to the point B. The points A and is adjusted to control the inductive reactance to compensate for B can be designated vice versa because of the dipole antenna capacitive coupling between the two radiating arms. The near symmetrical in shape. The antenna can easily be constructed from optimal value of the distance (d), in this case, is 1 mm. 1686 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 6, June 2008 DOI 10.1002/mop
  2. 2. Figure 4 Measured peak antenna gain and measured radiation effi- ciency. [Color figure can be viewed in the online issue, which is available Figure 2 Measured return loss for the proposed antenna; d 1 mm. at www.interscience.wiley.com] [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com] 4. CONCLUSION 3. RESULTS AND DISCUSSION A novel, flat, metal-plate dipole antenna capable of providing Figure 2 shows the measured return loss of a design prototype. For dual-band operation in the 2.4- and 5-GHz WLAN bands has been frequencies over the 2.4- and 5-GHz WLAN bands, the measured proposed. The antenna with a one-piece, metal-plate structure is impedance matching is all better than 10 dB, even better than 14 easy to implement and can be a promising solution for keeping the dB (about 1.5:1 VSWR), which meets the bandwidth specification cost down. The dual operating bands can easily be controlled by for 2.4/5-GHz WLAN operation easily. Figure 3 plots the far-field, the larger dipole and the smaller dipole arms obtained by cutting 3D radiation patterns at 2442, 5250, and 5775 MHz, measured at the L-shaped slits in the proposed design. Good radiation charac- the 3 3 7-m3 anechoic chamber at Lite-On Technology Corp., teristics of the proposed antenna have been also observed. Taipei. Across the operating bandwidth are observed good, omni- directional radiation patterns in the x–z plane, similar to the con- ventional, wire-dipole radiation characteristics. Note that the om- nidirectional radiation exists in the cut (the x–y plane in this case), REFERENCES that is a symmetrical plane, in geometry, for the proposed dipole 1. C.Y. Fang, H.T. Chen, and K.L. Wong, Printed uni-planar dual-band antenna. The measured peak antenna gain and the measured radi- monopole antenna, Microwave Opt Technol Lett 37 (2003), 452-454. ation efficiency are presented in Figure 4. The antenna gain in the 2. C.H. Lee and S.O. Park, A compact printed hook-shaped monopole 2.4-GHz band has a gain level of about 3.32 dBi, and the radiation antenna for 2.4/5-GHz WLAN applications, Microwave Opt Technol efficiency exceeds about 86%. In the 5-GHz band, the antenna gain Lett 48 (2006), 327-329. varies within a range of about 4.14 – 4.75 dBi, with radiation 3. V. Deepu, K.R. Rohith, J. Manoj, et al., Compact uniplanar antenna for efficiency of 92% and above. WLAN applications, Electron Lett 43 (2007), 70-72. 4. C.M. Su, H.T. Chen, and K.L. Wong, Printed dual-band dipole antenna with U-slotted arms for 2.4/5.2 GHz WLAN operation, Electron Lett 38 (2002), 1308-1309. 5. S.H. Hwang, J.I. Moon, W.I. Kwak, and S.O. Park, Printed compact dual band antenna for 2.4 and 5 GHz ISM band applications, Electron Lett 40 (2004), 1568-1569. 6. C.M. Su, W.S. Chen, and K.L. Wong, Compact dual-band metal-plate antenna for 2.4/5.2-GHz WLAN operation, Microwave Opt Technol Lett 38 (2003), 113-115. 7. C.Y. Fang, H.C. Tung, S.W. Su, and K.L. Wong, Narrow flat metal- plate antenna for dual-band WLAN operations, Microwave Opt Technol Lett 38 (2003), 398-400. © 2008 Wiley Periodicals, Inc. Figure 3 Measured 3D radiation patterns at 2442, 5250, and 5775 MHz. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com] DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 6, June 2008 1687

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