A three-antenna MIMO system capable of generating a wide operating bandwidth of 2400-5850 MHz for access-point applications is introduced. The proposed design is based on a bent metal-plate monopole antenna with a compact size of 20 × 20 × 14 mm3. The three antennas are equally spaced along the perimeter of a circular ground and all generate a wide bandwidth of larger than 4 GHz. With the antenna short-circuiting facing the center of the ground, not only the overall antenna size is reduced but also good isolation of less than -20 dB can easily be obtained. Calculated envelope correlation is also less than 0.002 across the operating band. The design prototype of the antenna is discussed in detail in the paper.

1. terahertz frequency. Meanwhile, the real dielectric constants of the monopole antenna with a compact size of 20 20 14 mm3. The three
No. 2 and No. 3 samples increases slowly with the THz wave antennas are equally spaced along the perimeter of a circular ground
frequencies. From the Figure 4(b), one sees that the imaginary and all generate a wide bandwidth of larger than 4 GHz. With the an-
dielectric constant of the No. 2 and No. 3 silicon samples decrease tenna short-circuiting facing the center of the ground, not only the over-
all antenna size is reduced but also good isolation of less than 20 dB
slightly with frequency and is nearly negligible. Note that the
can easily be obtained. Calculated envelope correlation is also less than
imaginary dielectric constant of the No. 1 increase rapidly as the
0.002 across the operating band. The design prototype of the antenna is
terahertz wave frequency is increased. The power loss in the discussed in detail in the article. © 2008 Wiley Periodicals, Inc.
dielectric can be expressed in terms of the loss tangent tan Microwave Opt Technol Lett 50: 1146 –1148, 2008; Published online in
/ . The main mechanism of THz field absorption is the Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.
dielectric loss caused by molecular collisions and vibrations. 23333
4. CONCLUSION Key words: antennas; monopole antennas; wideband antennas; access-
By using a THz-BWO system, the dielectric properties of various point antennas; MIMO antennas; WLAN antennas; WiMAX antennas
silicons in the THz region have been investigated systematically.
The refractive indices, the power absorption coefficients, and the 1. INTRODUCTION
complex dielectric constants of the silicon were measured and Recently, 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 devices
high resistivity silicon is a good candidate material for THz wave such 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-
ACKNOWLEDGMENTS ployed in the market for MIMO systems. However, from an
The authors acknowledge the excellent experiment by Dr Chen esthetic point of view, external antennas are not very pleasing to
and the helpful discussions with Dr. Li. This research was partially the end user. In this letter, we propose a wideband three-antenna
supported by the National Natural Science Foundation of China MIMO 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) [4] operation in the
REFERENCES 2400 –5850 MHz band. The wideband monopole antenna used in
1. H. Han, H. Park, M. Cho, and J. Kim, Terahertz pulse propagation in a the MIMO system is easily constructed by bending a metal plate
plastic photonic crystal fiber, Appl Phys Lett 80 (2002), 2634 –2636. into a compact structure. In addition, the antennas are arranged to
2. T.K. Ostmann, P. Dawson, K. Pierz, G. Hein, and M. Koch, Room- be equally spaced along the perimeter of a circular ground with the
temperature operation of an electrically driven terahertz modulator, antenna feeding located at the rim and the short-circuiting facing
Appl Phys Lett 84 (2004), 3555–3557. the center of the ground. In this case, highly isolated ports between
3. H. Kurt and D.S. Citrin, Photonic crystals for biochemical sensing in the any two antennas can easily be obtained. Details of the proposed
terahertz region, Appl Phys Lett 87 (2005), 041108.
antenna and the experimental results of a fabricated prototype are
4. T.-I. Jeon, J.-H. Son, G.H. An, and Y.H. Lee, Characterization of carbon
presented.
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 inflammable 2. ANTENNA DESIGN
liquids 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, and
Detection and identification of explosives using terahertz pulsed spec-
troscopic imaging, Appl Phys Lett 86 (2005), 241116.
3), which are all made of a 0.3-mm thick copper-nickel-zinc alloy,
7. N. Nagai, T. Imai, R. Fukasawa, K. Kato, and K. Yamauchi, Analysis occupies a space with the dimensions 20 20 14 mm3 and is
of the intermolecular interaction of nanocomposites by THz spectros- equally spaced along the perimeter of a circular ground. Detailed
copy, Appl Phys Lett 85 (2004), 4010 – 4012. dimensions of the antenna are shown in Figure 1(b). The antenna
8. Y.S. Jin, G.J. Kim, and S.G. Jeon, Terahertz dielectric properties of mainly comprises a shorted monopole antenna and a supporting
polymers, J Korean Phys Soc 49 (2006), 513–517. metal plate. The supporting metal plate can be also treated as the
antenna 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 the
ground. This arrangement largely helps the proposed MIMO sys-
tem achieve good isolation between any two of the three antennas.
Furthermore, by combining bending and short-circuiting [5] the
INTERNAL WIDEBAND MONOPOLE monopole antenna, the antenna height can be reduced to 14 mm,
ANTENNA FOR MIMO ACCESS-POINT about 11% wavelength of the lower-edge operating frequency at
APPLICATIONS IN THE WLAN/WIMAX 2400 MHz, which is smaller than the height of the conventional,
BANDS wideband-monopole antenna [5, 7, 8], usually about 18 –20%
Jui-Hung Chou and Saou-Wen Su
wavelength of the desired lower-edge operating frequency. In this
Technology Research Development Center, Lite-On Technology case, the proposed antenna is well suited for internal antenna
Corporation, Taipei 11492, Taiwan applications. For testing the MIMO antenna system, three short
50- mini-coaxial cables with I-PEX connectors are utilized. The
Received 24 September 2007 inner conductor of the coaxial cable is connected to the point A,
the feeding point and the outer, braided shielding is connected to
ABSTRACT: A three-antenna MIMO system capable of generating a the point B, the grounding point. When at mass production, the
wide operating bandwidth of 2400 –5850 MHz for access-point applica- coaxial cables can be bundled up in a shrunk tube for ease of cable
tions is introduced. The proposed design is based on a bent metal-plate routing (see demonstration of antenna arrangement in Fig. 2). Also
1146 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 5, May 2008 DOI 10.1002/mop

2. Figure 3 Measured refection coefficient (S11 for the antenna 1) and
isolation (S21) between the antennas 1 and 2. [Color figure can be viewed
in 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 antennas
1 and 2 are demonstrated for brevity.
3. RESULTS AND DISCUSSION
Figure 3 shows the measured reflection coefficient (S11) and iso-
lation (S21). Note that the Bands 1, 2, and 3 (see insets) represent
the WLAN and WiMAX bands of 2400 –2690, 3400 –3800, and
5150 –5850 MHz, respectively. It is first seen that the obtained
10 dB impedance bandwidth can easily cover the entire band of
2400 –5850 MHz, which meets the requirement of the operating
bandwidth for WLAN and WiMAX operation. For the isolation
between the antennas 1 and 2, the parameter S21 remains under
20 dB over the entire operating band. The envelope correlation
can be calculated via the following relation in terms of S param-
eters of the antenna system described in [9]:
S* S12
11 S* S22 2
21
Figure 1 (a) Proposed three-antenna (antennas 1, 2, and 3) MIMO e 2
1 S11 S21 2 1 S11 2 S12 2
system 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 4 Calculated envelope correlation between the antennas 1 and 2.
Figure 2 Photo of mass-production samples adhered to a plastic disc for [Color figure can be viewed in the online issue, which is available at
demonstration www.interscience.wiley.com]
DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 5, May 2008 1147

3. been proposed, constructed, and studied. The obtained bandwidths
of 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 between
any two antennas is less than 20 dB across the desired operating
bandwidth, even much less than 25 dB in the higher frequency
band. The three-antenna MIMO system has three highly isolated
ports with an envelop correction of less than 0.002. Good radiation
characteristics of the antenna have also been observed.
REFERENCES
1. C.C. Chiau, X. Chen, and C.G. Parini, A compact four-element diver-
sity- antenna array for PDA terminals in a MIMO system, Microwave
Opt Technol Lett 44 (2005), 408 – 412.
2. K.L. Wong, C.H. Chang, B. Chen, and S. Yang, Three-antenna MIMO
system for WLAN operation in a PDA phone, Microwave Opt Technol
Lett 48 (2006), 1238 –1242.
3. M. Manteghi and Y. Rahmat-Samii, A novel miniaturized triband PIFA for
MIMO 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 monopole
antenna, Electron Lett 35 (1999), 2157–2158.
Figure 5 Measured 3D radiation patterns for the antenna 1. [Color figure 6. 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 planar
lation values all remain under 0.002 in the bands of interest. The monopole 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 the 9. S. Blanch, J. Romeu, and I. Corbella, Exact representation of antenna
antenna 1 at 2545, 3600, and 5500 MHz, the center operating system diversity performance from input parameter description, Elec-
frequencies of the Bands 1, 2, and 3, respectively, measured at the tron Lett 39 (2003), 705–707.
3 3 7 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-
erating frequencies. Figure 6 presents the measured peak antenna A K-BAND LOW-NOISE AMPLIFIER
gain and radiation efficiency for the antenna 1. The peak antenna- USING SHUNT RC-FEEDBACK AND
gain levels are about 2.4, 2.5, and 3.6 dBi over the Bands 1, 2, and SERIES INDUCTIVE-PEAKING
3, respectively. For the measured radiation efficiency, it is found to TECHNIQUES
exceed about 73% over both the WLAN and WiMAX bands.
Chi-Chen Chen, Yo-Sheng Lin, Jin-Fa Chang, and
Jen-How Lee
4. CONCLUSION Department of Electrical Engineering, National Chi Nan University,
A MIMO system utilizing three compact wideband monopole Puli, Taiwan, Republic of China; Corresponding author:
antennas stamped from a metal plate in a wireless access point has stephenlin@ncnu.edu.tw
Received 25 September 2007
ABSTRACT: A 28.2 GHz (K-band) low-noise amplifier (LNA) using
standard 0.18- m CMOS technology was designed and implemented. To
achieve sufficient gain, this LNA was composed of three cascaded com-
mon-source stages, and a peaking inductor (Lg3) was added in the input
terminal of the third stage to boost the peak gain (S21) of 34.9% (simu-
lation). Shunt RC feedback was adopted in the second and the third
stage, respectively, for achieving good input and output impedance
matching. At 28.2 GHz, this LNA achieved input return loss (S11) of 13.4
dB, output return loss (S22) of 20.5 dB, forward gain (S21) of 12.9 dB,
reverse isolation (S12) of 50.2 dB, noise figure of 6.07 dB and input-re-
ferred 1-dB compression point (P1dB-in) of 10.8 dBm. The minimum noise
figure was 5.75 dB at 28.8 GHz. The chip area was only 950 m 590
m excluding the test pads. The power consumption was 30.56 mW from a
1.8-V power supply. © 2008 Wiley Periodicals, Inc. Microwave Opt
Technol Lett 50: 1148 –1152, 2008; Published online in Wiley Inter-
Figure 6 Measured peak antenna gain and measured radiation efficiency Science (www.interscience.wiley.com). DOI 10.1002/mop.23332
against frequency for the antenna 1. [Color figure can be viewed in the
online issue, which is available at www.interscience.wiley.com] Key words: K-band; CMOS; LNA; inductive peaking; RC feedback
1148 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 5, May 2008 DOI 10.1002/mop