A compact dual-WLAN-band antenna, in the shape of a paper clip, is presented. The antenna can easily be manufactured by bending few times a single copper wire with a length of about 65 mm, and operates in the 2.4 and 5.2 GHz bands in the WLAN environment. In addition to the simple configuration, the antenna is easily fed by 50- mini-coaxial cable, which allows it flexibility in a defined location for installation. An experimental prototype of the proposed antenna with the overall dimensions about 5 mm x 23.5 mm is constructed, tested, and demonstrated.

1. antenna for Bluetooth applications, Microwave Opt Technol Lett 48
(2006), 683– 686.
15. C.H. Wu, K.L. Wong, Y.C. Lin, and S.W. Su, Internal shorted monopole
antenna for the watch-type wireless communication device for Bluetooth
operation, Microwave Opt Technol Lett 49 (2007), 942–946.
16. Ansoft high frequency structure simulator (HFSS), Version 10.0, An-
soft Corporation, Pittsburgh, PA, 2005.
© 2008 Wiley Periodicals, Inc.
COMPACT PAPER-CLIP-SHAPED WIRE
ANTENNA FOR 2.4 AND 5.2 GHz WLAN
OPERATION
Saou-Wen Su,1 Jui-Hung Chou,1 and Yung-Tao Liu2
1
Technology Research Development Center, Lite-On Technology
Corporation, Taipei 11492, Taiwan; Corresponding author:
susw@ms96.url.com.tw
Figure 4 Simulated and measured proposed compact antenna gain for 2
Department of Physics, R.O.C. Military Academy, Feng-Shan
Bluetooth frequencies. [Color figure can be viewed in the online issue, 83059, Taiwan
which is available at www.interscience.wiley.com]
Received 10 February 2008
small enough to be embedded on module devices. Experimental
ABSTRACT: A compact dual-WLAN-band antenna, in the shape of a
results show that by choosing suitable combinations of these
paper clip, is presented. The antenna can be easily manufactured by
parameters, good impedance bandwidth and stable radiation pat- bending few times a single copper wire with a length of about 65 mm,
terns can be obtained. This proposed antenna has an impedance and it operates in the 2.4 and 5.2 GHz bands in the WLAN environment.
bandwidth (return loss 7.5 dB) of 170 MHz (2.37–2.54 GHz). In addition to the simple configuration, the antenna is easily fed by a
Within this impedance bandwidth, broadside radiation patterns are 50- mini-coaxial cable which allows it to be flexible in a defined loca-
observed and exhibited. Also, the measured peak gains, with gain tion for installation. An experimental prototype of the proposed antenna
variation less than 1.15 dBi, are obtained of 0.13–1.28 dBi. The with the overall dimensions of about 5 mm 23.5 mm is constructed,
proposed antenna is a good candidate for Bluetooth applications. tested, and demonstrated. © 2008 Wiley Periodicals, Inc. Microwave
Opt Technol Lett 50: 2572–2574, 2008; Published online in Wiley Inter-
Science (www.interscience.wiley.com). DOI 10.1002/mop.23760
REFERENCES
1. S. Pinhas and S. Shrikman, Comparison between computed and mea-
Key words: antennas; wire antennas; dual-band antennas; WLAN an-
sured bandwidth of quarter-wave microstrip radiator, IEEE Trans An-
tennas
tennas Propagat 36 (1988), 1615–1616.
2. R. Waterhouse, Small microstrip patch antenna, Electron Lett 31
(1995), 604 – 605. 1. INTRODUCTION
3. J.R. Games, A.J. Schuleer, and R.F Binham, Reduction of antenna Many coaxial-line-fed, standalone antennas of a small form factor
dimensions by dielectric loading, Electron Lett 10 (1974), 263–265. have been reported for many practical applications for WLAN
4. W.C. Tzou, H.M. Chen, Y.C. Chen, and C.F. Yang, Bandwidth en- operation [1– 6]. Owing to their flexibility and mobility, these
hancement of U-slot patch antenna on high permittivity ceramic sub-
kinds of antennas are very attractive to fit into many kinds of
strate for Bluetooth application, Microwave Opt Technol Lett 36
(2003), 499 –501.
wireless electronics devices for WLAN applications. For example,
5. D.H. Seo, S.G. Jeon, N.K. Kang, J. Ryu, and J.H. Choi, Design of a these antennas can be designed for installation in narrow spaces,
novel compact antenna for a Bluetooth LTCC module, Microwave Opt such as the space between the display and the housing of a laptop
Technol Lett 50 (2008), 180 –183. computer and a wireless digital frame, or be adhered to the internal
6. K.L. Wong and K.P Yang, Compact dual frequency microstrip antenna side of the housing of a wireless audio/video adapter. Further, with
with a pair of bent slots, Electron Lett 34 (1998), 225–226. respect to antenna structures, these kinds of antennas are in the
7. K.L. Wong and Y.F. Lin, Small broadband rectangular microstrip form of dielectric-substrate (or printed-circuit-board) antennas
antenna with chip-resistor loading, Electron Lett 33 (1997), 1593–1594. [1–3] and conductive, metal-plate antennas [4 – 6]. Little attention
8. Z. Zhuang, Z. Shen, and P. Shum, A compact inverted double-L has been given to the antenna structure made of a metal wire, like
antenna, Microwave Opt Technol Lett 48 (2006), 968 –969.
a spiral wire for a common helical antenna [7]. In this letter, we
9. M. Ali and G.J. Hayes, Small printed integrated inverted-F antenna for
Bluetooth application, Microwave Opt Technol Lett 33 (2002), 347–
present a thin metal wire antenna, which has the same merits of
349. those aforementioned, for operation in the 2.4 GHz (2400 –2484
10. J.P. Lee and S.O. Park, The meander line antenna for Bluetooth, MHz) and 5.2 GHz (5150 –5350 MHz) WLAN bands. The antenna
Microwave Opt Technol Lett 34 (2002), 149 –151. is obtained from a copper wire and bent few times to achieve
11. J.I. Mook and S.O. Park, Small chip dielectric antenna for Bluetooth compactness. The proposed antenna is ideal for integration into
application, Microwave Opt Technol Lett 39 (2003), 366 –368. WLAN applications. Details of the antenna design are described,
12. M.F. Karim and H.G. Shiraz, EBG-assisted slot antenna for Bluetooth and a constructed prototype is demonstrated.
applications, Microwave Opt Technol Lett 48 (2006), 482– 487.
13. M.Z. Azad and M. Ali, A new class of miniature embedded inverted-F
antenna for 2.4GHz WLAN application, IEEE Trans Antennas Propa- 2. ANTENNA DESIGN
gat 54 (2006), 2585–2592. Figure 1(a) shows the geometry, in detail, of the proposed antenna
14. L. Lu and J.C. Coetzee, Characteristics of a two-layer microstrip patch for operation in the 2.4 and 5.2 GHz band. In this study, the
2572 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 10, October 2008 DOI 10.1002/mop

2. Figure 2 Measured return loss for the design prototype. [Color figure
(a) can be viewed in the online issue, which is available at www.
interscience.wiley.com]
width (5 mm in this case) for the antenna, the distance is adjusted
by shifting both the feeding and the shorting points away from the
shorting portion. A near optimal value of 2 mm was selected.
Furthermore, by fine-tuning the length of the overlapped section
C–D [see Fig. 1(a)] in the longer radiating arm, well-matched
(b)
Figure 1 (a) Detailed geometry of the dual-band copper-wire antenna for
WLAN operation. (b) Photo of a working sample fed by 50- mini-coaxial
cable. [Color figure can be viewed in the online issue, which is available at
www.interscience.wiley.com]
antenna is made of a thin copper wire of about 65 mm in length
and of diameter 0.8 mm, and can be easily fabricated by bending
few times the wire into a paper-clip shape. The proposed antenna
consists mainly of a shorter radiating arm, a longer radiating arm,
(a)
and a shorting portion that links both the radiating arms. The
shorter radiating arm provides a resonant path for upper resonant
mode at 5.25 GHz. On the other hand, the longer radiating arm
dominates the antenna lower resonant mode for the 2.4-GHz band
operation and also, in part, functions as the antenna ground plane.
The overall size of the antenna in the form of a rectangle is with
the dimensions 5 mm 23.5 mm. A photo of a working sample of
the design prototype is presented in Figure 1(b). As seen in the
photo, a short 50- mini-coaxial cable with an I-PEX connector is
utilized to feed the wire antenna in the experiment. The inner
conductor of the coaxial cable is connected to the point A, the
feeding point, at the shorter radiating arm; the outer, braided
shielding is connected to the point B, the grounding point, at the
longer radiating arm.
For matching the input impedance over the 2.4 and 5.2 GHz
bands, the distance between the feeding and the shorting points (b)
were first determined. This distance has major effect on the achiev-
able bandwidth, similar to matching a monopole PIFA [8 –10], in Figure 3 Measured radiation patterns for the antenna studied in Figure
which the distance from the shorting strip to the antenna feeding 2: (a) at 2442 MHz; (b) at 5250 MHz. [Color figure can be viewed in the
point largely affects the impedance matching. With the predefined online issue, which is available at www.interscience.wiley.com]
DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 10, October 2008 2573

3. antenna for 2.4/5-GHz WLAN applications, Microwave Opt Technol
Lett 48 (2006), 327–329.
3. V. Deepu, K.R. Rohith, J. Manoj, et al., Compact uniplanar antenna for
WLAN applications, Electron Lett 43 (2007), 70 –72.
4. C.Y. Fang, H.C. Tung, S.W. Su, and K.L. Wong, Narrow flat metal-
plate antenna for dual-band WLAN operations, Microwave Opt Tech-
nol Lett 38 (2003), 398 – 400.
5. J.H. Chou and S.W. Su, Cost-effective metal-plate shorted dipole
antenna with wide bandwidth for WLAN/WiMAX applications, Mi-
crowave Opt Technol Lett 49 (2007), 3044 –3046.
6. S.W. Su, J.H. Chou, and Y.T. Liu, A one-piece flat-plate dipole
antenna for dual-band WLAN operation, Microwave Opt Technol Lett
50 (2008), 678 – 680.
7. J.D. Kraus and R.J. Marhefka, Antennas: For all applications, 3rd ed.,
McGraw-Hill, New York, NY, 2001.
8. K.L. Wong, Y.Y. Chen, S.W. Su, and Y.L. Kuo, Diversity dual-band
Figure 4 Measured peak antenna gain and radiation efficiency for the planar inverted-F antenna for WLAN operation, Microwave Opt Tech-
antenna studied in Figure 2. [Color figure can be viewed in the online issue, nol Lett 38 (2003), 223–225.
which is available at www.interscience.wiley.com] 9. S.W. Su, C.H. Wu, W.S. Chen, and K.L. Wong, Broadband printed
-shaped monopole antenna for WLAN operation, Microwave Opt
Technol Lett 41 (2004), 269 –270.
impedance over the operation bands can be achieved. This length 10. K.L. Wong, M.R. Hsu, W.Y. Li, S.W. Su, and A. Chen, Study of the
controls the additional capacitive reactance between the section Bluetooth headset antenna with the user’s head, Microwave Opt Tech-
C–D and the shorter radiating arm, which can also compensate for nol Lett 49 (2007), 19 –23.
inductive coupling contributed to the shorting portion.
© 2008 Wiley Periodicals, Inc.
3. EXPERIMENTAL RESULTS AND DISCUSSION
Figure 2 shows the measured reflection coefficient of a constructed
prototype. For frequency range of interest, a 2000 – 6000 MHz
spectrum was selected in the network analyzer. It is easy to see that
the impedance matching in both the 2.4 and 5.2 GHz bands is less
VARACTOR-TUNED MICROSTRIP
than 7.3 dB. Figures 3(a) and 3(b) give the measured radiation
BANDPASS FILTER WITH WIDE
patterns at 2442 and 5250 MHz, respectively. The far-field 2D TUNING RANGE
radiation patterns were measured at a 3 3 7 m3 fully anechoic Jeongpyo Kim and Jaehoon Choi
chamber (to simulate a free-space environment) at Lite-On Tech- Department of Electrical and Computer Engineering, Hanyang
nology Corp., Taipei. The chamber is in fact a 3D measurement University 17 Haengdang-Dong, Seongdong-Gu, Seoul 133-791,
system using the great-circle method and equipped with a dual- Korea; Corresponding author: choijh@hanyang.ac.kr
polarized horn (receiving antenna). Measurements at other fre-
quencies of the 2.4 and 5.2 GHz bands of WLAN operation were Received 18 February 2008
also taken, and the results showed similar radiation patterns as
those plotted here. In the x–y plane were observed omnidirectional ABSTRACT: In this study, a tunable bandpass filter with a hairpin line
radiation patterns across the operating frequencies. The measured resonator and loading capacitors using varactor diodes was proposed.
peak antenna gain and radiation efficiency are shown in Figure 4. The filter was modified by adding varactor diodes to the coupling part
The peak-gain level in the 2.4 GHz band is about 2.0 dBi, and the to compensate for losses. The designed filter had a simple structure and
the characteristics of wide tuning range of 87.9% from 430 to 1105
radiation efficiency exceeds about 82%. As for the 5.2 GHz band,
MHz and low insertion loss of less than 4.42 dB. © 2008 Wiley Peri-
the peak gain is in the range of 2.8 –3.3 dBi with the radiation odicals, Inc. Microwave Opt Technol Lett 50: 2574 –2577, 2008;
efficiency larger than 90%. Notice that the radiation efficiency was Published online in Wiley InterScience (www.interscience.wiley.com).
obtained in the 3D test system (software) by calculating the total DOI 10.1002/mop.23745
radiated power of the antenna under test over the 3D spherical
radiation and then dividing the sum by the input power (default Key words: tunable filter; SDR; hairpin
value of 0 dBm here).
4. CONCLUSION 1. INTRODUCTION
A new, compact, copper-wire antenna ideal for WLAN operation The growth of mobile communications requires the design of
in the 2.4 and 5.2 GHz bands has been proposed and studied in this miniaturized, multi- standard/multi-band, low-cost transceivers.
article. The measured results show that dual-band WLAN opera- These need various tunable or reconfigurable components includ-
tion with good radiation property has been obtained for the design ing a filter for software-defined radio (SDR) systems or multi-band
prototype. The proposed antenna with a single wire configuration systems. To cover the commercial communication services in
is easy to implement and can be a good candidate for the internal these systems, the tuning range of the tunable filter must be
WLAN antenna, especially for the use in some internal spaces extended by at least 2:1. However, the desired wide tuning range
within communications devices. causes the insertion loss at the lowest resonant frequency [1–3].
An active filter that uses a negative resistance with an amplifier
REFERENCES is utilized to compensate for the insertion loss. The active filter can
1. C.Y. Fang, H.T. Chen, and K.L. Wong, Printed uni-planar dual-band achieve an insertion gain or a near zero dB insertion loss. Thus, the
monopole antenna, Microwave Opt Technol Lett 37 (2003), 452– 454. drawback of the tunable filter with wide tuning range can be
2. C.H. Lee and S.O. Park, A compact printed hook-shaped monopole overcome by using an active filter with a negative resistance
2574 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 50, No. 10, October 2008 DOI 10.1002/mop