6. H.-M. Kim and B. Lee, Bandgap and slow/fast-wave characteristics of     ducted for the task, including cutting slits in...
Figure 4 Measured isolation (S21, S31, S32) between any two of the three
                                                 ...
Figure 6 Measured 2-D radiation patterns at 5490 MHz for dipole antenna 1 studied in Fig. 3. [Color figure can be viewed in...
Figure 8 Measured 2-D radiation patterns at 5490 MHz for dipole antenna 2 studied in Fig 3. [Color figure can be viewed in ...
10. J. H. Chou and S. W. Su, Internal wideband monopole antenna for             WiMAX frequency band. A simple formula for...
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A Three-in-One Diversity Antenna System for 5 GHz WLAN Applications

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A novel, three-in-one antenna system suitable for WLAN operation in the 5 GHz band is presented. The design is based upon incorporating one slot and two dipole antennas into a compact multi-antenna system that has comparable dimensions of a single mobile-unit antenna element. The three antennas are arranged parallel to each other with the two dipoles set on the right and left sides of the slot respectively. With this arrangement, not only can compact integration of three individual antennas be realized, pattern diversity and polarization diversity are also obtained. A design prototype has been constructed and tested. The results show that the coupling or the antenna port isolation is below –20 dB and good radiation characteristics have been observed.

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A Three-in-One Diversity Antenna System for 5 GHz WLAN Applications

  1. 1. 6. H.-M. Kim and B. Lee, Bandgap and slow/fast-wave characteristics of ducted for the task, including cutting slits in the ground [1–3], defected ground structures (DGSs) including left-handed features, arranging antenna shorted portions facing each other [4, 5, 10], IEEE Trans Microwave Tech 54 (2006), 3113–3120. manipulating radiation polarization of two closely-spaced antennas 7. S.-W. Ting, K.-W. Tam, and R.P. Martins, Miniaturized microstrip [6, 7], and so on. Notice that most of these designs are based on the lowpass filter with wide stopband using double equilateral U-shaped multiple antennas excited on the same ground plane. Little atten- defected ground structure, IEEE Microwave Wireless Compon Lett 16 tion has been given to integrating individual, small antennas into (2006), 240 –242. 8. H.W. Liu, Z.F. Li, and X.W. Sun, A novel fractal defected ground one unity. structure and its application to the low-pass filter, Microwave Opt In this article we present a compact multiantenna system that Technol Lett 39 (2003), 453– 455. merges three individual antennas (each has its antenna feed port 9. Y.-Q. Fu, N.-C. Yuan, and G.-H. Zhang, A novel fractal microstrip and signal ground) into one antenna unity. The three antennas PBG structure, Microwave Opt Technol Lett 32 (2002), 136 –138. consist of one slot antenna and two dipole antennas and are etched 10. S. Jung, Y.-K. Lim, and H.-Y. Lee, A coupled-defected ground struc- on the same layer of a dielectric substrate in a coplanar configu- ture lowpass filter using inductive coupling for improved attenuation, ration. The two dipole antennas are symmetrically placed on the Microwave Opt Technol Lett 50 (2008), 1541–1543. right and left sides of the slot antenna with any two of the three 11. J.-Y. Kim and H.-Y. Lee, Wideband and compact bandstop filter antennas parallel to each other. With this configuration, the an- structure using double-plane superposition, IEEE Microwave Wireless tenna system is able to provide both pattern diversity and polar- Compon Lett 13 (2003), 279 –280. ization diversity and at the same time, to attain highly isolated © 2009 Wiley Periodicals, Inc. ports of the three antennas. A prototype of the design example targeted at the 5 GHz [5.2 GHz (5150-5350 MHz) and 5.8 GHz (5725-5825 MHz)] band operation is constructed, demonstrated, and tested. Detailed description of the proposed antenna system A THREE-IN-ONE DIVERSITY ANTENNA and design consideration thereof is given and elaborated in the article. SYSTEM FOR 5 GHZ WLAN APPLICATIONS 2. ANTENNA CONFIGURATION AND DESIGN CONSIDERATIONS Saou-Wen Su Network Access Strategic Business Unit, Lite-On Technology Figure 1 shows the configuration of the proposed, three-in-one, Corporation, Taipei County 23585, Taiwan; Corresponding author: diversity antenna system etched on a single-layered, 1-mm-thick stephen.su@liteon.com, susw@msm FR4 substrate with the dimensions 30 mm 27 mm. The diversity antenna system mainly comprises one slot antenna and two dipole Received 30 December 2008 antennas, all formed on the same layer of the dielectric substrate in a coplanar configuration (see Fig. 2). In the center of the substrate ABSTRACT: A novel, three-in-one antenna system suitable for is located the slot antenna with the dimensions 30 mm 15 mm. WLAN operation in the 5 GHz band is presented. The design is The width and length of the slot is chosen to be of 2.5 mm and 23.9 based upon incorporating one slot and two dipole antennas into a mm respectively. In this case the ground-plane width of the slot compact multiantenna system that has comparable dimensions of a antenna is six times that of the slot, whose length corresponds to single mobile-unit antenna element. The three antennas are arranged about 0.44-wave-length ( c) at the center operating frequency, parallel to each other with the two dipoles set on the right and left sides of the slot respectively. With this arrangement, not only can 5490 MHz in the 5 GHz band, of the antenna. Notice that the compact integration of three individual antennas be realized, pattern diversity and polarization diversity are also obtained. A design pro- totype has been constructed and tested. The results show that the coupling or the antenna port isolation is below 20 dB and good radiation characteristics have been observed. © 2009 Wiley Periodi- cals, Inc. Microwave Opt Technol Lett 51: 2477–2481, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24606 Key words: antennas; printed antennas; dipole antennas; slot antennas; diversity antennas; WLAN antennas 1. INTRODUCTION Multiantenna designs have been favorable to applications in the WLAN environment. These designs of the applications in wireless systems include antenna diversity [1–7] and multiple-input multi- ple-output (MIMO) system [8 –11]. Antenna diversity is well- known for the counter to effects of multipath and can enhance the performance of wireless communications systems. For MIMO system, multiple transmit and receive antennas are used to increase data throughput without additional spectrum. MIMO system can also make use of multipath propagation to improve signal quality and reliability. One of the most important tasks for multiantenna designs is to achieve low mutual coupling (high isolation) and low Figure 1 Proposed, three-in-one, diversity antenna system and detailed correlation. This is not easy to accomplish when the two antennas dimensions thereof. [Color figure can be viewed in the online issue, which are located in close proximity. Several researches have been con- is available at www.interscience.wiley.com] DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 10, October 2009 2477
  2. 2. Figure 4 Measured isolation (S21, S31, S32) between any two of the three antennas of the proposed, diversity antenna system. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley. com] Figure 2 Photo of a design prototype constructed from a 1-mm-thick To achieve polarization diversity, the slot and dipole antennas FR4 substrate. [Color figure can be viewed in the online issue, which is are used and arranged to be parallel to each other. This horizontal available at www.interscience.wiley.com] configuration of the slot and dipole antennas allows the two antenna ports to be easily decoupled (port isolation 20 dB), feeding (denoted as Port 2 in Fig. 1) for the slot antenna is about and at the same time, orthogonal polarization is realized. As for the 7.5 mm from the bottom of the slot. This distance effects imped- effect of pattern diversity, the radiation of the two dipoles are ance matching and center operating frequency in the 5 GHz band expected to cover space on both sides (right and left) of the slot, largely. Further, the two dipole antennas are put on the right and whose main radiation is in the front and back directions of the left sides of the slot antenna and to be symmetrical in arrangement. proposed multiantenna system. Finally, to feed the design proto- The near optimal value of the dipole-antenna length and feed gap type, three short, 50- mini-coaxial cables with I-PEX connectors is found to be 17 mm and 1 mm respectively. Usually, for two are utilized. parallel dipoles, to obtain isolation well below 15 dB between the dipoles that have good input matching of 10 dB return loss, a 3. RESULTS AND DISCUSSION minimal space of 0.65 c (that’s 36 mm versus 23 mm here) is On the basis of design dimensions given in Figure 1, the proposed, required between the antennas [12]. However, the slot antenna three-in-one, diversity antenna system was constructed and tested. here can be treated as a reflector, which not only reflects the dipole Figure 3 shows the measured reflection coefficients (S11 for dipole radiation but decouples the two dipole antennas. Also notice that antenna 1, S22 for slot antenna, S33 for dipole antenna 2). Port further moving the dipole antenna towards the ground plane of the isolation (S21, S31, S32) between any two of the three antennas for slot antenna can lead to deteriorating bandwidth for the dipole the proposed design is shown in Figure 4. It can easily be seen that antenna. A near optimal distance of 4 mm is selected in this study. measured impedance bandwidth of the three antennas meets the required bandwidth specification for 5 GHz WLAN operation with Figure 3 Measured reflection coefficients (S11 for dipole antenna 1, S22 for slot antenna, S33 for dipole antenna 2) of the proposed, diversity Figure 5 Calculated envelope correlation for the three 5 GHz antennas. antenna system. [Color figure can be viewed in the online issue, which is [Color figure can be viewed in the online issue, which is available at available at www.interscience.wiley.com] www.interscience.wiley.com] 2478 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 10, October 2009 DOI 10.1002/mop
  3. 3. Figure 6 Measured 2-D radiation patterns at 5490 MHz for dipole antenna 1 studied in Fig. 3. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com] reflection coefficient well below 10 dB. The isolation between (simulated) as described in [13] for sufficiently accurate results in the two dipoles is found to be below 20 dB over the 5 GHz band. many practical cases [13, 14]. The correlation values remain under This good decoupling is expected because the ground plane of the 0.002 in the band, which is better than the value of 0.3 demanded slot antenna is considered as a reflector lying in between the two widely by industry specification. dipole antennas. As for the isolation between the dipole and slot Figures 6 – 8 plot the far-field, 2-D radiation patterns at 5490 antennas, due to symmetrical structure of the proposed, diversity MHz, the center operating frequency of the 5 GHz band, for the antenna system, the curves of S21 and S32 are about the same. In three antennas. Firstly, for the two dipole antennas, directional addition, better decoupling in the band of interest, compared with radiation patterns are found in the x-y and x-z planes with maxi- the isolation between the two dipoles, has been observed largely mum radiation (peak antenna gain) in the x directions ( x for because of the dipole and slot antennas set to be of orthogonal dipole 1 and x for dipole 2, see Figs. 6 and 8). This behavior is polarization. Figure 5 gives the envelope correlation between port expected due largely to the ground plane of the slot antenna acting 1 (of dipole antenna 1) and port 2 (of slot antenna). Notice that the as a reflector. On the contrary very little effect of the reflector is envelope correlation here is determined by the use of S parameters given on the radiation in the y-z plane of the two dipoles. Secondly, Figure 7 Measured 2-D radiation patterns at 5490 MHz for the slot antenna studied in Fig 3. [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. 51, No. 10, October 2009 2479
  4. 4. Figure 8 Measured 2-D radiation patterns at 5490 MHz for dipole antenna 2 studied in Fig 3. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com] the slot antenna yields typical, bi-directional radiation patterns in cations. To attain the proposed design, one slot antenna and two the x-y and y-z planes with peak antenna gain around the y dipoles antennas have been employed and integrated into a com- directions as seen in Figure 7. Worth noticing that along the y pact structure on a substrate of 30 mm 27 mm. Experimental axes at the intersection of three principal-polarization radiation of results show that good isolation of less than 20 dB between any the slot and dipole antennas, the maximum radiation in the E field two antenna ports has been obtained, along with envelope corre- of the dipole is at the right angle to the maximum radiation in the lation well below 0.002 over the 5 GHz band. Directional radiation E field of the slot. The properties indicate that orthogonal waves patterns have been observed to cover complementary space in of polarization diversity take place. Figure 9 presents the peak addition to orthogonal waves formed by the slot and dipole anten- antenna gain against frequency for the antennas studied in Figure nas. The design of the proposed, three-in-one antenna system is a 3. The peak gain over the 5 GHz band for the three antennas is seen promising solution to internal diversity antennas in the 5 GHz to be at a constant level of about 4 dBi. In addition, it can easily band. be seen that the antenna gain of the two dipole antennas is similar due to symmetrical structure of the proposed design. REFERENCES 4. CONCLUSION 1. T. Ohishi, N. Oodachi, S. Sekine, and H. Shoki, A method to improve the correlation coefficient and the mutual coupling for diversity an- A small three-antenna system capable of providing pattern diver- tenna, IEEE Antennas Propagat Soc Int Symp Dig, Washington, DC sity and polarization diversity and having low mutual coupling has (2005), 507–510. been designed, fabricated and measured for 5 GHz WLAN appli- 2. G. A. Mavridis, J. N. Sahalos, and M. T. Chryssomallis, Spatial diversity two-branch antenna for wireless devices, Electron Lett 42 (2006), 266 –268. 3. C. Y. Chiu, C. H. Cheng, R. D. Murch, and C. R. Rowell, Reduction of mutual coupling between closely-packed antenna elements, IEEE Trans Antennas Propagat 55 (2007), 1732–1738. 4. K. L. Wong, Y. Y. Chen, and S. W. Su, Diversity dual-band planar inverted-F antenna for WLAN operation, Microwave Opt Technol Lett 38 (2003), 223–225. 5. S. W. Su, J. H. Chou, and T. Y. Wu, Internal broadband diversity dipole antenna, Microwave Opt Technol Lett 49 (2007), 810 – 812. 6. S. C. K. Ko and R. D. Murch, A diversity antenna for external mounting on wireless handsets, IEEE Trans Antennas Propagat 49 (2001), 840 – 842. 7. F. Thudor and A. Louzir, An extremely compact pattern diversity antenna for WLAN, IEEE Antennas Propagat Soc Int Symp Dig, San Antonio, TX (2002), 60 – 63. 8. C. C. Chiau, X. Chen, and C. G. Parini, A compact four-element diversity-antenna array for PDA terminals in a MIMO system, Micro- wave Opt Technol Lett 44 (2005), 408 – 412. Figure 9 Measured peak antenna gain for the three antennas studied in 9. M. Manteghi and Y. Rahmat-Samii, A novel miniaturized triband Fig. 3. [Color figure can be viewed in the online issue, which is available PIFA for MIMO applications, Microwave Opt Technol Lett 49 (2007), at www.interscience.wiley.com] 724 –731. 2480 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 10, October 2009 DOI 10.1002/mop
  5. 5. 10. J. H. Chou and S. W. Su, Internal wideband monopole antenna for WiMAX frequency band. A simple formula for calculating the reso- MIMO access-point applications in the WLAN/WiMAX bands, Mi- nant frequency is given. The antenna is simple in configuration out- crowave Opt Technol Lett 50 (2008), 1146 –1148. lining an overall dimension of 44 20 0.76 mm3. The measured 11. S. W. Su, J. H. Chou, and Y. T. Liu, Printed coplanar two-antenna 10 dB bandwidth for return loss is from 2.37 to 2.7, 3.23 to 3.70, element for 2.4/5 GHz WLAN operation in a MIMO system, Micro- and 4.29 to 6.58 GHz for WiMAX and WLAN applications. © 2009 wave Opt Technol Lett 50 (2008), 1635–1638. Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2481–2485, 12. S. W. Su and Y. T. Liu, Realization of dual-dipole-antenna system for 2009; Published online in Wiley InterScience (www.interscience.wiley. concurrent dual-radio operation using polarization diversity, Micro- com). DOI 10.1002/mop.24650 wave Opt Technol Lett, in press. 13. J. Thaysen and K. B. Jakobsen, Envelope correlation in (N, N) MIMO Key words: broadband antenna; triple band antenna; rectangular antenna array from scattering parameters, Microwave Opt Technol monopole; circular disc monopole Lett 48 (2006), 832– 834. 14. V. Plicanic, Z. Ying, T. Bolin, G. Kristensson, and A. Derneryd, Antenna diversity evaluation for mobile terminals, Eur Conf Antennas 1. INTRODUCTION Propagat (2006), 1–3. The interest in research and design of multiband and broadband antennas has increased dramatically in recent years, with the boost © 2009 Wiley Periodicals, Inc. in modern wireless communication systems. Several multiband antenna designs for wireless local area network (WLAN) have been reported. The reported popular design configurations meeting A NOVEL TRIPLE BAND PRINTED the dual band operation for local area network in the 2.4 GHz ANTENNA FOR WLAN/WiMAX (2.4 –2.484 GHz) and 5.2/5.8 GHz (5.15–5.35 GHz/5.725–5.825 APPLICATIONS GHz) bands include a microstrip-fed double-T monopole antenna [1], a CPW-fed monopole antenna with two resonant paths [2], a K. George Thomas and M. Sreenivasan C-shaped monopole antenna with a shorted parasitic element [3], SAMEER-Centre for Electromagnetics, CIT Campus, 2nd Cross an inverted-L monopole with meandered wire and conducting Road, Taramani, Chennai-600113, India; Corresponding author: gt2781964@gmail.com triangular section [4], a dual band WLAN dipole antenna [5], a branched monopole antenna with a truncated ground plane [6] and a microstrip-fed dual band coplanar antenna [7]. The dual band slot Received 7 January 2009 antenna with double T-match stub generates resonance at 2.35– 2.55 and 5– 6 GHz [8]. However, none of the above available ABSTRACT: A new microstrip-fed triple band antenna is presented for satisfying wireless local area network (WLAN) and worldwide designs can support worldwide interoperability for microwave interoperability for microwave access (WiMAX) applications simulta- access (WiMAX) application. Various kinds of antenna suitable neously. The antenna comprises a rectangular monopole fed by a for WLAN/WiMAX operation were reported. The microsrtrip line microstrip transmission line to generate WLAN and WiMAX fre- fed slot antennas possess advantages such as wide impedance quency bands and a circular disc monopole to resonate in 3.5 GHz bandwidth, low profile, light weight and easy to manufacture [9], Figure 1 Configuration of the proposed triple band printed antenna lf 16.5 mm, wf 1.4 mm, r 8 mm, lg 15 mm, wg 20 mm, g 1.5 mm, h 20 mm, w 10 mm, l 27.5 mm, L 44 mm, H 0.76 mm DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 51, No. 10, October 2009 2481

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