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1                                    return losses larger than 15 dB indicate that the input ports and
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demonstrated. © 2008 Wiley Periodicals, Inc. Microwave Opt
Technol Lett 50: 2403–2407, 2008; Published online in Wiley Int...
(a)




                                                                          (b)

Figure 3 Measured radiation pattern...
Figure 4 Measured peak antenna gain and measured radiation efficiency
for the antenna studied in Figure 2 with U stubs 1 an...
MINIATURIZED IMPLANTABLE
                                                                               BROADBAND ANTENNA ...
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Printed Omnidirectional Access-Point Antenna for 2.4/5-GHz WLAN Operation

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A new design of the printed omnidirectional antenna for applications in 2.4/5-GHz dual-WLAN-band access points is proposed. The antenna consists of a conventional collinear antenna for 2.4 GHz operation and two U stubs for 5 GHz operation. The two U stubs are located near the points where the maximum currents at about 5.5 GHz occurring on the strips of the collinear antenna, and arranged back to back in the same phase for achieving better antenna gain. Detailed analyses of the U stub on the impedance matching over the 5 GH band is presented. A prototype with good omnidirectional radiation across the 2.4/5-GHz WLAN bands is demonstrated.

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Transcript of "Printed Omnidirectional Access-Point Antenna for 2.4/5-GHz WLAN Operation"

  1. 1. 1 return losses larger than 15 dB indicate that the input ports and f z5 . (5) three frequency bands match well. The measured values of isola- 2 L 32C 33 tion between two frequency bands of the output ports of the triplexer are shown in Figure 8(b). When signal frequencies are greater than 2.4 GHz, signals can pass the 2.4-GHz output port (port 4). The 2.4-GHz HPF is 4. CONCLUSION composed of two shunt resonant pairs L41, C42 and L42, C44 and A newly developed triplexer has been proposed in this article. connected with one capacitor C43. The capacitor C41 is used to This triplexer is very suitable to implement on the multichip match with 1.9-GHz LPF. The frequencies of two transmission module because of its high integration and compact size. In- zeros generated in the 2.4-GHz HPF are as serting the transmission zero can enhance the isolation among three passbands. The agreement between measurement and the- 1 oretical prediction has demonstrated the feasibility of this f z6 , (6) study. 2 L 41C 42 ACKNOWLEDGMENTS 1 f z7 . (7) This work was supported in part by the National Science Council, 2 L 42C 44 Taiwan, R.O.C., under grant NSC 96-2628-E-194-002-MY2 and NSC 96-2623-7-194-004-D. 3. SIMULATION AND EXPERIMENTAL RESULTS REFERENCES The frequency bands of our proposed triplexer are set at 0.9/1.8/ 2.4-GHz. In the 1.0-GHz LPF, the corresponding component val- 1. T. Ohno, K. Wada, and O. Hashimoto, Design methodologies of planar duplexers and triplexers by manipulating attenuation poles, IEEE Trans ues in Figure 4 are L11 4.49 nH, C11 1.64 pF, C12 4.67 pF, Microwave Theory Tech 53 (2005), 2088 –2095. L12 6.16 nH, C13 0.686 pF, and C14 3 pF. Frequencies of 2. C.W. Tang and S.F. You, Design methodologies of LTCC bandpass two transmission zeros fz1 and fz2 are obtained according to (1) and filters, diplexer and triplexer with transmission zeros, IEEE Trans (2) as 1.85 and 2.45 GHz, respectively, shown in Figure 5(a). Microwave Theory Tech 54 (2006), 717–723. Signals with a higher frequency can go through the 1.7-GHz HPF. 3. R.J. Wenzel, Printed-circuit complementary filters for narrow band- The corresponding component values are C21 2.2 pF, L21 6.15 width multiplexers, IEEE Trans Microwave Theory Tech MTT-16 nH, and C22 3.5 pF, C23 0.9 pF. The frequency of the (1968), 147–157. transmission zero fz3 is obtained according to (3) as 1.085 GHz 4. C.C. Rocha, A.J.M. Soares, and H. Abdalla, Jr, Microwave multiplexers shown in Figure 5(a). The corresponding component values of using complementary filters, Applied Microwave & Wireless, January/ matching circuit are L22 4 nH, C24 2.14 pF. February 1998, pp. 28 –36. 5. C.Q. Scrantom and J.C. Lawson, LTCC technology: Where we are and In the 1.9-GHz LPF, the corresponding component values are where we’re going-II, IEEE MTT-S International Microwave Sympo- L31 1.51 nH, C31 3 pF, C32 1.64 pF, L32 1.6 nH, and C33 sium Digest 1999, Anaheim, CA pp. 193–200. 2.54 pF. Frequencies of two transmission zeros fz4 and fz5, 6. C.W. Tang, J.W. Sheen, and C.Y. Chang, Chip-type LTCC-MLC bal- shown in Figure 5(a), are obtained according to (4) and (5) as 2.36 uns using the stepped impedance method, IEEE Trans Microwave and 2.5 GHz, respectively, while the rest of signals go through the Theory Tech 49 (2001), 2342-2349. 2.4-GHz HPF. The corresponding component values are C41 7. W.Y. Leung, K.K.M. Cheng, and K.L. Wu, Multilayer LTCC bandpass 0.89 pF, L41 8 nH, C42 0.8 pF, C43 0.98 pF, L42 11.5 nH, filter design with enhanced stopband characteristics, IEEE Microwave and C44 0.67 pF. Frequencies of two transmission zeros fz6 and Wireless Comp Lett 12 (2002), 240-242. fz7 are obtained according to (6) and (7) as 2 and 1.8 GHz, respectively, shown in Figure 5(a). These parameters can then be © 2008 Wiley Periodicals, Inc. substituted into a circuit simulator, such as ADS or equivalent software, to carry out the circuit simulation. After circuit simulation, these values are converted into the PRINTED OMNIDIRECTIONAL ACCESS- LTCC structure, and the circuit size is 210 mil 210 mil 40.5 mil shown in Figure 6. The simulation is carried out with the POINT ANTENNA FOR 2.4/5-GHZ WLAN assistance of the full-wave electromagnetic (EM) simulator Sonnet OPERATION (Sonnet Software, North Syracuse, NY). Figure 8 shows the results Saou-Wen Su and Jui-Hung Chou of EM simulation, which match well with that of circuit simulation Technology Research Development Center, Lite-On Technology shown in Figure 5. The multilayered LTCC triplexer was fabri- Corporation, Taipei 11492, Taiwan; Corresponding author: cated on a Dupont 951 substrate. Its dielectric constant and loss susw@ms96.url.com.tw tangent are 7.8 and 0.0045, respectively. This LTCC triplexer is designed on four upper layers with the 1.57 mil sheet, six middle Received 1 January 2008 layers with the 3.6 mil sheet, four following layers with the 1.57 mil sheet, and two lowest layers with the 3.6 mil sheet. Figure 7 ABSTRACT: A new design of the printed omnidirectional antenna shows the three-dimensional (3-D) architecture of the fabricated for applications in 2.4/5-GHz dual-WLAN-band access points is pro- triplexer. posed. The antenna consists of a conventional collinear antenna for 2.4 GHz operation and two U stubs for 5 GHz operation. The two U An on-wafer tester has been employed in order to improve the stubs are located near the points where the maximum currents at accuracy of measurement. The network analyzer, Agilent N5230A about 5.5 GHz occurring on the strips of the collinear antenna and PNA_L, is used for measurement, whereas the short-open-load- arranged back-to-back in the same phase for achieving better an- through (SOLT) is used for calibration. As shown in Figure 8(a), tenna gain. Detailed analyses of the U stub on the impedance match- the measured insertion losses are less than 0.5, 1.3, and 1.4 dB in ing over the 5 GH band is presented. A prototype with good omnidi- the frequency bands of 0.9, 1.8, and 2.4 GHz, respectively. The rectional radiation across the 2.4/5-GHz WLAN bands is DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 9, September 2008 2403
  2. 2. demonstrated. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 2403–2407, 2008; Published online in Wiley Inter- Science (www.interscience.wiley.com). DOI 10.1002/mop.23629 Key words: antennas; printed antennas; omnidirectional antennas; WLAN antennas 1. INTRODUCTION Printed collinear antennas with omnidirectional radiation are at- tractive to applications of access points, routers, and gateways in WLAN [1-4]. Except for the multisection microstrip antenna re- ported in [4], the printed collinear antenna, in general, comprises (a) (b) Figure 2 (a) Measured and simulated return loss for the antenna with U stubs 1 and 2. (b) Measured return loss with U stub 1, U stubs 1 and 2, and without U stubs 1 and 2. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com] a ground, quarter-wavelength and half-wavelength sections, and a phase reversal. One can easily manipulate the peak gain of this kind of antenna by cascading further more half-wavelength sec- tions together with phase reversals. However, for these referenced antennas, the antennas are merely operating in the single band and cannot provide dual-band 2.4/5-GHz (2400-2484/5150-5825 MHz) WLAN operation. This motivates us to find a simple solu- tion for obtaining a dual-band omnidirectional antenna, based on the conventional collinear antenna reported in [1-3]. In this letter, we demonstrate a new design of a printed omnidirectional antenna capable of dual-band operation in the 2.4/5 GHz bands. To some degree, the proposed antenna is derived from the 2.4 GHz collinear antenna reported in [2] for 2.4 GHz operation, and furthermore, two U stubs of proper size are carefully added to the antenna for achieving the 5 GHz operation. Details of the design consideration of the proposed antenna are described, and the results are presented and discussed. Figure 1 (a) Detailed dimensions of the printed omnidirectional antenna for a 2.4/5-GHz WLAN access point. (b) Photo of a mass-production 2. ANTENNA DESIGN AND CONFIGURATION sample for the antenna with a plastic housing. [Color figure can be viewed Figure 1(a) shows the geometry of the proposed access-point in the online issue, which is available at www.interscience.wiley.com] antenna, and a photo of a working sample for mass production is 2404 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 9, September 2008 DOI 10.1002/mop
  3. 3. (a) (b) Figure 3 Measured radiation patterns for the antenna studied in Fig. 2 with U stubs 1 and 2: (a) at 2442 MHz; (b) at 5490 MHz. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com] demonstrated in Figure 1(b). The antenna mainly consists of a ductivity 0.02 S/m). That is, all the data in the next section conventional 2.4-GHz collinear antenna [2], and two U stubs were obtained under the conditions, in which the antenna was arranged back-to-back. Notice that a hollow metal cylinder (diam- installed within the housing. eter 4 mm) soldered to the ground portion is used for manufac- The 2.4-GHz collinear antenna (the proposed antenna without ture purposes. The hollow structure also allows a 50- minicoaxial U stubs) can be considered as two half-wavelength elements cable (the inner conductor connected to the feed point A; the outer bridged by such a half-wavelength phase reversal that both of the braided shielding connected to the ground point B) to get through. elements have in-phase currents, which result in constructive ra- Also, notice that the plastic housing [see Fig. 1(b) but not drawn in diation [2]. For upper frequencies in the 5 GHz band, the element Fig. 1(a) for brevity] is taken into account in this study for both 1 (comprising the section 1, ground and metal cylinder) and measurement and simulation (relative permittivity r 3.5, con- element 2 (the section 2) become one-wave -length resonant struc- DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 9, September 2008 2405
  4. 4. Figure 4 Measured peak antenna gain and measured radiation efficiency for the antenna studied in Figure 2 with U stubs 1 and 2. [Color figure can be viewed in the online issue, which is available at www.interscience. Figure 6 Simulated return loss as a function of g for the antenna with a wiley.com] U stub 1. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com] tures and have out-of-phase currents with two current nulls in each element. It has been found that by adding a U stub of proper size MHz. When adding first one U stub to the antenna section 1, much to the antenna around the feed point A, where the maximum wider bandwidth with better impedance matching can be achieved. current occurs, much wider achievable bandwidth for 5 GHz As for the proposed design [denoted as with stubs 1 and 2 in Fig. operation can be obtained. Furthermore, the second U stub (the 2(b)], the lower-edge frequency and the return loss is about the same size as the first stub) is added to the section 2 around the same as that for the antenna with a single U stub 1 only. That is, portion where the maximum current is seen and arranged back-to- adding one more stub to the initial antenna with a single U stub 1 back for in-phase currents for better antenna gain. Notice that the is not considered in this case to have a major impact on the desired maximum-current occurrence is very close the center of the section impedance bandwidth of the proposed antenna. 2; thus, the U stub 2 is connected to the antenna in about the Figures 3(a) and (b) plot the measured radiation patterns for the middle of the section 2. Because the 5-GHz impedance bandwidth antenna with the U stubs 1 and 2 at 2442 and 5490 MHz. Dipole- can be much improved by adding a single U stub 1 to the antenna, like radiation patterns are obtained, and good omnidirectional the analyses here only focus on the effects of the U stub 1 for radiation in the horizontal (x–y) plane with gain variation less than brevity. Once the near optimal size of the U stub 1 is decided, the 1.5 dBi is seen. In the elevation plane are also found side lobes in U stub 2 will be as the same. The results will be elaborated more the radiation at 5490 MHz, which is due largely to the overall fully in the next section. resonant path of the antenna (excluding the path for meandered currents in the phase reversal) longer than two wavelengths at 3. RESULTS AND DISCUSSION about 5.5 GHz and also the null current distribution on the sections Figure 2(a) shows the measured and simulated return loss. For the 1 and 2 and the metal cylinder. The radiation patterns for the 2.4/5 GHz bands, the impedance matching is all within VSWR of conventional 2.4-GHz collinear antenna [shown as w/o stubs 1 and two. Notice that when there are no stubs at all [denoted as w/o 2 in Fig. 2(b)] at 2442 and 5490 MHz were measured too. No stubs 1 and 2 in Fig. 2(b)], one resonant mode with relatively much difference in the radiation patterns (normalized in respect of narrow bandwidth in the 5 GHz band is excited at about 5420 the largest gain in each plane) between the proposed and conven- tional antennas was observed. This behavior is expected mainly because the stubs have major effects on the impedance matching and are also beneficial for the 5-GHz-band antenna gain. The measured antenna gain and radiation efficiency are shown in Figure 4. The peak gain in the 2.4 GHz band has a gain level of about 4.1 dBi, and the radiation efficiency exceeds about 80%. As for the 5 GHz band, the peak gain level reaches about 3.4 dBi, with radiation efficiency in a range of 79 – 85%. For better understanding, the function of the U stub in terms of matching the antenna in the 5 GHz band, the simulation studies on the analyses of the parameters d, g, and L of the U stub (see each inset in Figs. 5–7) were made. Because adding the U stub 2 (in addition to the U stub 1) to the antenna does not affect the antenna’s upper frequencies to a great degree, and the analyses here only focus on the parametric effect of the U stub 1 for brevity. Figure 5 shows the return-loss results for the small distance d varying from 3 to 5 mm. For 5 GHz operation, the lower-edge frequency decreases as the value d increases, which is due to an Figure 5 Simulated return loss as a function of d for the antenna with a increase in the overall resonant path (stating from the feeding point U stub 1. [Color figure can be viewed in the online issue, which is available A) for upper frequencies. Notice that the lower frequencies, the at www.interscience.wiley.com] 2.4-GHz band, are almost unaffected in this case. Effects of the 2406 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 9, September 2008 DOI 10.1002/mop
  5. 5. MINIATURIZED IMPLANTABLE BROADBAND ANTENNA FOR BIOTELEMETRY COMMUNICATION Wen-Chung Liu,1 Feng-Ming Yeh,2 and Mohammad Ghavami3 1 Department of Aeronautical Engineering, National Formosa University, 64 Wenhua Road, Huwei, Yunlin 632, Taiwan, Republic of China; Corresponding author: wencliu@nfu.edu.tw 2 Institute of Electro-Optical and Materials Science, National Formosa University, 64 Wenhua Road, Huwei, Yunlin 632, Taiwan, Republic of China 3 Department of Electronic Engineering, King’s College London, Strand, London WC2R 2LS, United Kingdom Received 4 January 2008 ABSTRACT: A body-implantable miniaturized and broadband stacked antenna suitable for biotelemetry communication is proposed. By prop- Figure 7 Simulated return loss as a function of L for the antenna with a erly arranging a rectangular three-layer slotted patch structure, the de- U stub 1. [Color figure can be viewed in the online issue, which is available signed antenna with only 10 10 1.9 mm3 can provide a 10 dB at www.interscience.wiley.com] impedance bandwidth of 50 MHz in the 402– 405 MHz medical-implant- communication-service frequency band. When compared with the re- ported most compact antenna, the proposed design achieves not only a more monopole-like radiation pattern with a double-radiation efficiency gap g between the U stub 1 and the section 1 are shown in Figure of 0.61% but also a size reduction of 43%. © 2008 Wiley Periodicals, 6. Once again, the lower-edge frequency for 5 GHz operation Inc. Microwave Opt Technol Lett 50: 2407–2409, 2008; Published on- decreases when the value g increases due to increased resonant line in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ path too. Characteristics of the 5-GHz impedance matching for mop.23649 different values of g are, however, about the same, compared with those for various distances of d in Figure 5. Not much variation in Key words: compact; implantable antenna; PIFA; biotelemetry commu- the return-loss curves is also found for 2.4 GHz operation. Figure nication; MICS 7 shows the return loss as a function of the length L. It can be seen that the impedance matching and bandwidth are largely affected 1. INTRODUCTION for upper frequencies. The larger value of L can result in better Recently, there is growing research activity on short-range wire- matching in the 5 GHz band, and L 8 mm is chosen for the less telemedicine application for treating human diseases and moderate effect. monitoring various physiological parameters. As the physiological signals are wirelessly transceived between implantable medical devices and exterior equipment at some defined medical-implant- 4. CONCLUSION communication-service (MICS) frequency bands such as 403/868/ A printed access-point antenna with omnidirectional radiation 915 MHz and 2.4 GHz, the antenna, with compact size and good characteristics for 2.4/5-GHz dual-band WLAN operation been radiating performance, suitable for implanting inside a human introduced, and a design prototype has been fabricated and tested. body, is thus becoming a critical component for the biotelemetry It has been found that by adding the U stubs to a conventional communication. To reduce the antenna size and broaden the im- 2.4-GHz collinear antenna, a wide operating band covering the pedance bandwidth, the stacked planar inverted-F antenna (PIFA) required bandwidth of the 5 GHz WLAN band can be effectively structure is the most used design technology. So far, several such achieved in addition to the 2.4 GHz band. Good omnidirectional kinds of antennas have been proposed, including the circular radiation has been obtained across the operating bands too. The stacked PIFA [1], the meandered PIFA [2], and the spiral PIFAs proposed antenna is promising for applications in the WLAN [3, 4]. However, although the antenna reported in [1] has the most access point, especially in the environment where dual-band op- compact size of only 1.9 mm3, these antennas are still either eration is demanded by the end user. large in antenna structure or narrow in bandwidth for practical applications. In this letter, we present a novel design of a rectangular three-layer stacked PIFA antenna with a miniaturized antenna size REFERENCES and a broad bandwidth suitable for use in biotelemetry communi- 1. K. M. Luk and S. H. Wong, A printed high-gain monopole antenna for cation at the 402– 405 MHz frequency band. The case for the indoor wireless LANs, Microwave Opt Technol Lett 41 (2004), 177- proposed design is that it is not only capable of providing higher 180. radiation efficiency and better monopolelike pattern but also 2. K. L. Wong, T. C. Tseng, F. R. Hsiao, and T. W. Chiu, High-gain achieve more size reduction with 43% than the reported work [1]. omnidirectional printed collinear antenna, Microwave Opt Technol Lett Details of the antenna design and both theoretical and experimen- 44 (2005), 348-351. tal results are presented and discussed. 3. MaxBeam60 embedded smart antenna, Airgain, 2007, available at http://www. airgain.com/A2460.html. 4. R. Bancroft, Design parameters of an omnidirectional planar microstrip 2. ANTENNA CONFIGURATION antenna, Microwave Opt Technol Lett 47 (2005), 414-418. Figure 1 illustrates the geometry of the proposed miniaturized implantable broadband antenna for MICS 403 MHz band opera- © 2008 Wiley Periodicals, Inc. tion. The dimensions of the antenna were first studied by simula- DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 9, September 2008 2407

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