Compact Vertical Patch Antenna for Dual-Band WLAN Operation

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A new compact patch antenna, which is arranged perpendicular to a circular ground plane, for WLAN operation is presented. The antenna consists mainly of one driven patch and one shorted parasitic patch, which both wind along two concentric circles. A constructed prototype covering the 2.4 and 5 GHz WLAN bands is demonstrated. Good broadside radiation characteristics are obtained across the operating bands. Details of the proposed patch antenna and experimental results are presented and discussed.

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Compact Vertical Patch Antenna for Dual-Band WLAN Operation

  1. 1. Compact vertical patch antenna for The lengths of the two radiating strips for the driven and parasitic dual-band WLAN operation patches are about 30 and 85 mm, respectively. Both radiating strips rotate in the opposite direction (anticlockwise v. clockwise). The pro- F.-S. Chang, K.-C. Chao, C.-H. Lu and S.-W. Su posed antenna is fed using a 50 V SMA connector with the centre probe of length 3 mm connected to the driven patch through a triangular A new compact patch antenna, which is arranged perpendicular to a transition [2]. By adjusting the flare angle of the triangular transition circular ground plane, for WLAN operation is presented. The (optimal angle 908), wide operating bandwidth above 20% can be antenna consists mainly of one driven patch and one shorted parasitic achieved and easily cover the 5 GHz band. Further, to properly excite patch, both of which wind along two concentric circles. A constructed a lower resonant mode for 2.4 GHz operation, the location and width prototype covering the 2.4 and 5 GHz WLAN bands is demonstrated. of the shorting portion need to be considered. It has been found that Good broadside radiation characteristics are obtained across the operat- shorting the radiating strip of the parasitic patch in the vicinity of the ing bands. Details of the proposed patch antenna and experimental antenna feed point (17 mm away) with a 5-mm-wide shorting portion results are presented and discussed. can have near optimal 2.4 GHz operation. Introduction: Conventional patch antennas usually have a large radiat- Results: Fig. 2 shows the measured return loss. The impedance matching ing plate disposed above a finite ground plane, and for convenience, a for frequencies across the 2.4 and 5 GHz bands is all better than 10 dB (or short probe pin is utilised to excite the patch. Despite the merit of within VSWR of 2) and even below the line of 14 dB return loss for 5 GHz being low profile, they suffer typically from a few per cent of bandwidth. operation. Fig. 3 gives the measured radiation patterns for the antenna To solve this inherent problem of narrow bandwidths, the patch antenna studied in Fig. 2. The results for three different operating frequencies at with a thick air-layer substrate has been reported to provide a wide impe- 2442, 5250 and 5775 MHz are presented. Notice that all the patterns are dance bandwidth [1, 2]. In addition to broadband operation, studies have normalised with respect to the maximum radiation intensity in each also been made to attain dual-band operation by stacking patches [3] or plane. It is clearly seen that, in general, broadside radiation patterns are inserting a pair of slots/slits into the patch close to the non-radiating obtained. Also notice that, probably due to the monopole-like resonant edges [4]. However, these antennas still occupy a large space and projec- structure, the radiation properties are different from those of dual-band tion area (an area when the patch is perpendicularly projected onto the patch antennas [4, 6], in which the cross-polarisation in the E-plane is ground) to an extent. Recently, the circular vertical patch antenna has normally small, while that in the H-plane is relatively large and often been proposed to reduce the area of the patch [5, 6]. Although it is symmetrical in shape on both half spaces. The measured peak antenna simple in geometry, the circumference of the patch is about one wave- gain is shown in Fig. 4. In the 2.4 GHz band is the peak gain in the length of the operating frequency. In this Letter, a dual-band vertical range 6.5–7.3 dBi. As for the 5 GHz band, the peak antenna gain is patch antenna in the shape of a circular arc is proposed. The dual- between 5.3 and 7.3 dBi. When enhanced antenna gain is further requested, band operation is achieved by combining one driven patch and one para- an extra cavity structure can easily be utilised to increase gain level [7]. sitic patch of the antenna. The length of the circular arc of each patch is only half of the circumference of the circular vertical patch, giving less 0 material cost in mass production. The antenna can operate in the 2.4 GHz (2400– 2484 MHz) and 5 GHz (5150– 5825 MHz) WLAN 10 return loss, dB bands with broadside radiation. Details of the antenna design and experi- mental results of a prototype are presented and discussed. 20 Antenna design: Fig. 1 shows the geometry of the proposed dual- 30 2.4 GHz 5 GHz band WLAN-band vertical patch antenna mounted on a circular ground band plane. The antenna comprises a driven patch for 5 GHz operation and 40 2000 3000 4000 5000 6000 a shorted parasitic patch for 2.4 GHz operation. Both patches are in frequency, MHz the shape of a circular arc and wind along two concentric circles. With this arrangement, the antenna is able to occupy much less space Fig. 2 Measured return loss for proposed antenna compared with a large projection area that a conventional patch antenna usually has. Moreover, different from the circular vertical q = 0° (+z ) y q = 0° (+z ) patch the circumference of which is about one wavelength of the x operating frequency [5, 6], the driven and parasitic patches are about z half-wavelength resonant structures, i.e. the proposed antenna can be –30 dB manufactured at low cost with less material cost. –40 dB –90° 90° –90° 90° (+x ) (+y ) x-z plane f = 2442 MHz y-z plane ound (diameter r gr =9 q = 0° (+z ) q = 0° (+z ) ula 0 c irc m shorting m ) 90° sh –30 dB orte –40 dB iven atch 7 7 –90° 90° –90° 90° d parastic feed point (+x ) (+y ) p 15 dr 25 pa tc h x-z plane f = 5250 MHz y-z plane q = 0° (+z ) q = 0° (+z ) –30 dB parasitic patch 90° –40 dB 90° 5 –90° –90° 3 (+x ) (+y ) 3 5 5 mm driven patch shorting portion circular ground 50 SMA connector x-z plane f = 5775 MHz y-z plane Fig. 1 Configuration of proposed vertical patch antenna with two concentric radiating patches Fig. 3 Measured radiation patterns at 2442, 5250, 5775 MHz ELECTRONICS LETTERS 8th May 2008 Vol. 44 No. 10
  2. 2. 11 References antenna gain, dBi 9 1 Luk, K.M., Mak, C.L., Chow, Y.L., and Lee, K.F.: ‘Broadband microstrip patch antenna’, Electron. Lett., 1998, 34, (15), pp. 1442–1443 7 2 Chang, F.S., and Wong, K.L.: ‘A broadband probe-fed patch antenna for a DCS base station’, Microw. Opt. Technol. Lett., 2001, 30, (5), 5 pp. 341– 343 3 Dahele, J.S., Lee, K.F., and Wong, D.P.: ‘Dual frequency stacked 3 annular-ring microstrip antenna’, IEEE Trans. Antennas Propag., 1987, 2400 2450 2500 5150 5500 5850 35, (11), pp. 1281–1285 frequency, MHz 4 Kuo, Y.L., and Wong, K.L.: ‘A planar inverted-L patch antenna for 2.4/ 5.2-GHz dual-band operation’, Microw. Opt. Technol. Lett., 2001, 31, Fig. 4 Measured peak antenna gain (5), pp. 394– 396 5 Mak, C.L., Luk, K.M., and Lee, K.F.: ‘Geometry of wideband small- Conclusions: A dual-band vertical patch antenna, constructed by sized antenna: vertical patch antenna’, Electron. Lett., 2003, 39, (25), bending two radiating strips of metal plates, for WLAN operation is pre- pp. 1777–1779 6 Lau, K.L., Wong, H., Mak, C.L., Luk, K.M., and Lee, K.F.: ‘A vertical sented. A prototype mounted on a circular ground plane has been patch antenna for dual-band operation’, IEEE Antennas Wirel. Propag. implemented and tested. Although the diameter of the circular arc for Lett., 2006, 5, pp. 95–97 each patch is larger, the linear length of the patch here is only 50% of 7 Su, S.W., Wong, K.L., Cheng, Y.T., and Chen, W.S.: ‘High-gain the circumference of the circular vertical patch (i.e. less material cost). broadband patch antenna with a cavity ground for 5-GHz WLAN In addition, the proposed antenna can provide dual-band 2.4/5 GHz operation’, Microw. Opt. Technol. Lett., 2004, 41, (5), pp. 397–399 operation with broadside radiation. The antenna can be quite practical in applications of ceiling-mount access points. # The Institution of Engineering and Technology 2008 16 March 2008 Electronics Letters online no: 20080742 doi: 10.1049/el:20080742 F.-S. Chang and C.-H. Lu (Department of Electrical Engineering, R.O.C. Military Academy, Feng-Shan 83059, Taiwan) K.-C. Chao (Department of Electronics, Cheng Shiu University, Kaohsiung County 83347, Taiwan) S.-W. Su (Technology Research Development Center, Lite-On Technology Corp., Taipei 11492, Taiwan) E-mail: stephen.su@liteon.com ELECTRONICS LETTERS 8th May 2008 Vol. 44 No. 10

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