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terahertz frequency. Meanwhile, the real dielectric constants of themonopole antenna with a compact size of 202014 mm3. The threeNo. 2 and No. 3 samples increases slowly with the THz waveantennas are equally spaced along the perimeter of a circular groundfrequencies. From the Figure 4(b), one sees that the imaginaryand all generate a wide bandwidth of larger than 4 GHz. With the an-dielectric constant of the No. 2 and No. 3 silicon samples decreasetenna short-circuiting facing the center of the ground, not only the over-all antenna size is reduced but also good isolation of less than20 dBslightly with frequency and is nearly negligible. Note that thecan easily be obtained. Calculated envelope correlation is also less thanimaginary dielectric constant of the No. 1 increase rapidly as the0.002 across the operating band. The design prototype of the antenna isterahertz wave frequency is increased. The power loss in thediscussed in detail in the article. © 2008 Wiley Periodicals, Inc.dielectric can be expressed in terms of the loss tangent tanMicrowave Opt Technol Lett 50: 1146 –1148, 2008; Published online in/. The main mechanism of THz ﬁeld absorption is theWiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.dielectric loss caused by molecular collisions and vibrations.233334. CONCLUSIONKey words: antennas; monopole antennas; wideband antennas; access-By using a THz-BWO system, the dielectric properties of variouspoint antennas; MIMO antennas; WLAN antennas; WiMAX antennassilicons in the THz region have been investigated systematically.The refractive indices, the power absorption coefﬁcients, and the1. INTRODUCTIONcomplex dielectric constants of the silicon were measured andRecently, multiple-input multiple-output (MIMO) technology us-analyzed. The results obtained in this study suggest that the ultra-ing multiple internal antennas has been applied to mobile deviceshigh resistivity silicon is a good candidate material for THz wavesuch as mobile or PDA phones to obtain increases in data through-integrated circuit and ultra-low loss transmission waveguides.put [1–3]. As for applications of access points, conventional ex-ternal dipole and/or monopole antennas are still commonly em-ACKNOWLEDGMENTSployed in the market for MIMO systems. However, from anThe authors acknowledge the excellent experiment by Dr Chenesthetic point of view, external antennas are not very pleasing toand the helpful discussions with Dr. Li. This research was partiallythe end user. In this letter, we propose a wideband three-antennasupported by the National Natural Science Foundation of ChinaMIMO system suitable for being embedded in a wireless access(No. 60577023), China Postdoctoral Science Foundation.point for WLAN (2400 –2484/5150 –5825 MHz) and WiMAX(2495–2690/3400 –3800/5250 –5850 MHz)  operation in theREFERENCES2400 –5850 MHz band. The wideband monopole antenna used in1. H. Han, H. Park, M. Cho, and J. Kim, Terahertz pulse propagation in athe MIMO system is easily constructed by bending a metal plateplastic photonic crystal ﬁber, Appl Phys Lett 80 (2002), 2634 –2636.into a compact structure. In addition, the antennas are arranged to2. T.K. Ostmann, P. Dawson, K. Pierz, G. Hein, and M. Koch, Room-be equally spaced along the perimeter of a circular ground with thetemperature operation of an electrically driven terahertz modulator,antenna feeding located at the rim and the short-circuiting facingAppl Phys Lett 84 (2004), 3555–3557.the center of the ground. In this case, highly isolated ports between3. H. Kurt and D.S. Citrin, Photonic crystals for biochemical sensing in theany two antennas can easily be obtained. Details of the proposedterahertz region, Appl Phys Lett 87 (2005), 041108.antenna and the experimental results of a fabricated prototype are4. T.-I. Jeon, J.-H. Son, G.H. An, and Y.H. Lee, Characterization of carbonpresented.nanotubes by THz time domain spectroscopy, J Korean Phys Soc 39(2001), S185–S188.5. T. Ikeda, A. Matsushita, M. Tatsuno, et al, Investigation of inﬂammable2. ANTENNA DESIGNliquids by terahertz spectroscopy, App Phys Lett 87 (2005), 034105.Figure 1(a) shows the three-antenna MIMO system for access-6. Y.C. Shen, T. Lo, P.F. Taday, B.E. Cole, W.R. Tribe, and M.C. Kemp,point applications. Each of the three antennas (antennas 1, 2, andDetection and identiﬁcation of explosives using terahertz pulsed spec-3), which are all made of a 0.3-mm thick copper-nickel-zinc alloy,troscopic imaging, Appl Phys Lett 86 (2005), 241116.7. N. Nagai, T. Imai, R. Fukasawa, K. Kato, and K. Yamauchi, Analysisoccupies a space with the dimensions 202014 mm3 and isof the intermolecular interaction of nanocomposites by THz spectros-equally spaced along the perimeter of a circular ground. Detailedcopy, Appl Phys Lett 85 (2004), 4010 – 4012.dimensions of the antenna are shown in Figure 1(b). The antenna8. Y.S. Jin, G.J. Kim, and S.G. Jeon, Terahertz dielectric properties ofmainly comprises a shorted monopole antenna and a supportingpolymers, J Korean Phys Soc 49 (2006), 513–517.metal plate. The supporting metal plate can be also treated as theantenna ground. The antenna feeding is located at the rim of the© 2008 Wiley Periodicals, Inc.circular ground, while the shorting strip faces the center of theground. This arrangement largely helps the proposed MIMO sys-tem achieve good isolation between any two of the three antennas.INTERNAL WIDEBAND MONOPOLEFurthermore, by combining bending and short-circuiting  theANTENNA FOR MIMO ACCESS-POINTmonopole antenna, the antenna height can be reduced to 14 mm,about 11% wavelength of the lower-edge operating frequency atAPPLICATIONS IN THE WLAN/WIMAX2400 MHz, which is smaller than the height of the conventional,BANDSwideband-monopole antenna [5, 7, 8], usually about 18 –20%wavelength of the desired lower-edge operating frequency. In thisJui-Hung Chou and Saou-Wen SuTechnology Research Development Center, Lite-On Technologycase, the proposed antenna is well suited for internal antennaCorporation, Taipei 11492, Taiwanapplications. For testing the MIMO antenna system, three short50-mini-coaxial cables with I-PEX connectors are utilized. TheReceived 24 September 2007inner conductor of the coaxial cable is connected to the point A,the feeding point and the outer, braided shielding is connected toABSTRACT: A three-antenna MIMO system capable of generating athe point B, the grounding point. When at mass production, thewide operating bandwidth of 2400 –5850 MHz for access-point applica-coaxial cables can be bundled up in a shrunk tube for ease of cabletions is introduced. The proposed design is based on a bent metal-platerouting (see demonstration of antenna arrangement in Fig. 2). Also1146MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 5, May 2008DOI 10.1002/mopFigure 3Measured refection coefﬁcient (Sfor the antenna 1) and11isolation (S ) between the antennas 1 and 2. [Color ﬁgure can be viewed21in the online issue, which is available at www.interscience.wiley.com]note that due to the three identical antennas symmetrical in ar-rangement, only experimental results, in the study, of the antennas1 and 2 are demonstrated for brevity.3. RESULTS AND DISCUSSIONFigure 3 shows the measured reﬂection coefﬁcient (S ) and iso-11lation (S ). Note that the Bands 1, 2, and 3 (see insets) represent21the WLAN and WiMAX bands of 2400 –2690, 3400 –3800, and5150 –5850 MHz, respectively. It is ﬁrst seen that the obtained10 dB impedance bandwidth can easily cover the entire band of2400 –5850 MHz, which meets the requirement of the operatingbandwidth for WLAN and WiMAX operation. For the isolationbetween the antennas 1 and 2, the parameter Sremains under2120 dB over the entire operating band. The envelope correlationcan be calculated via the following relation in terms of S param-eters of the antenna system described in :S*211S12S*21S22eFigure 1(a) Proposed three-antenna (antennas 1, 2, and 3) MIMO1S 222211S211S11S12system for access-point applications. (b) Detailed dimensions of the inter-nal wideband antenna. [Color ﬁgure can be viewed in the online issue,Figure 4 shows that between the antennas 1 and 2, the corre-which is available at www.interscience.wiley.com]Figure 4Calculated envelope correlation between the antennas 1 and 2.Figure 2Photo of mass-production samples adhered to a plastic disc for[Color ﬁgure can be viewed in the online issue, which is available atdemonstrationwww.interscience.wiley.com]DOI 10.1002/mopMICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 5, May 20081147been proposed, constructed, and studied. The obtained bandwidthsof the antennas all cover both the 2.4/5-GHz WLAN and 2.5/3.5/5-GHz WiMAX bands. The results show that the isolation betweenany two antennas is less than20 dB across the desired operatingbandwidth, even much less than25 dB in the higher frequencyband. The three-antenna MIMO system has three highly isolatedports with an envelop correction of less than 0.002. Good radiationcharacteristics of the antenna have also been observed.REFERENCES1. C.C. Chiau, X. Chen, and C.G. Parini, A compact four-element diver-sity- antenna array for PDA terminals in a MIMO system, MicrowaveOpt Technol Lett 44 (2005), 408 – 412.2. K.L. Wong, C.H. Chang, B. Chen, and S. Yang, Three-antenna MIMOsystem for WLAN operation in a PDA phone, Microwave Opt TechnolLett 48 (2006), 1238 –1242.3. M. Manteghi and Y. Rahmat-Samii, A novel miniaturized triband PIFA forMIMO applications, Microwave Opt Technol Lett 49 (2007), 724 –731.4. WiMAX Forum, http://www.wimaxforum.org.5. E. Lee, P.S. Hall, and P. Gardner, Compact wideband planar monopoleantenna, Electron Lett 35 (1999), 2157–2158.Figure 5Measured 3D radiation patterns for the antenna 1. [Color ﬁgure6. M.J. Ammann, Square planar monopole antenna, IEE Antennas Propa-can be viewed in the online issue, which is available at www.interscience.gat Natl Conf (1999), 37– 40.wiley.com]7. M.J. Ammann and Z.N. Chen, Wideband monopole antennas for multi-band wireless systems, IEEE Antennas Propagat Mag 45 (2003), 146 –150.8. S.W. Su, K.L. Wong, and C.L. Tang, Ultra-wideband square planarlation values all remain under 0.002 in the bands of interest. Themonopole antenna for IEEE 802.16a operation in the 2–11-GHz band,* stands for conjugate.Microwave Opt Technol Lett 42 (2004), 463– 466.Figure 5 plots the measured 3D radiation patterns for the9. S. Blanch, J. Romeu, and I. Corbella, Exact representation of antennaantenna 1 at 2545, 3600, and 5500 MHz, the center operatingsystem diversity performance from input parameter description, Elec-frequencies of the Bands 1, 2, and 3, respectively, measured at thetron Lett 39 (2003), 705–707.337 m3 anechoic chamber at Lite-On Technology, Taipei.The radiation characteristics here are nearly similar to those of© 2008 Wiley Periodicals, Inc.wideband planar monopole antennas [6 –9], in which omnidirec-tional radiation patterns are obtained for the lower operating fre-quencies, while bidirectional radiation patterns for the higher op-A K-BAND LOW-NOISE AMPLIFIERerating frequencies. Figure 6 presents the measured peak antennagain and radiation efﬁciency for the antenna 1. The peak antenna-USING SHUNT RC-FEEDBACK ANDgain levels are about 2.4, 2.5, and 3.6 dBi over the Bands 1, 2, andSERIES INDUCTIVE-PEAKING3, respectively. For the measured radiation efﬁciency, it is found toTECHNIQUESexceed about 73% over both the WLAN and WiMAX bands.Chi-Chen Chen, Yo-Sheng Lin, Jin-Fa Chang, andJen-How Lee4. CONCLUSIONDepartment of Electrical Engineering, National Chi Nan University,A MIMO system utilizing three compact wideband monopolePuli, Taiwan, Republic of China; Corresponding author:antennas stamped from a metal plate in a wireless access point email@example.comReceived 25 September 2007ABSTRACT: A 28.2 GHz (K-band) low-noise ampliﬁer (LNA) usingstandard 0.18- m CMOS technology was designed and implemented. Toachieve sufﬁcient gain, this LNA was composed of three cascaded com-mon-source stages, and a peaking inductor (L ) was added in the inputg3terminal of the third stage to boost the peak gain (S ) of 34.9% (simu-21lation). Shunt RC feedback was adopted in the second and the thirdstage, respectively, for achieving good input and output impedancematching. At 28.2 GHz, this LNA achieved input return loss (S ) of13.411dB, output return loss (S ) of20.5 dB, forward gain (S ) of 12.9 dB,2221reverse isolation (S ) of50.2 dB, noise ﬁgure of 6.07 dB and input-re-12ferred 1-dB compression point (P) of10.8 dBm. The minimum noise1dB-inﬁgure was 5.75 dB at 28.8 GHz. The chip area was only 950m590m excluding the test pads. The power consumption was 30.56 mW from a1.8-V power supply. © 2008 Wiley Periodicals, Inc. Microwave OptTechnol Lett 50: 1148 –1152, 2008; Published online in Wiley Inter-Science (www.interscience.wiley.com). DOI 10.1002/mop.23332Figure 6Measured peak antenna gain and measured radiation efﬁciencyagainst frequency for the antenna 1. [Color ﬁgure can be viewed in theonline issue, which is available at www.interscience.wiley.com]Key words: K-band; CMOS; LNA; inductive peaking; RC feedback1148MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 5, May 2008DOI 10.1002/mop