bow-tie wide-band monopole antenna with the novel impedance

Figure 5 First experimental curves in the case of a 10.4-mm-thick PVC
slab at F 8.5 GHz in transmission
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© 2002 Wiley Periodicals, Inc.
ACKNOWLEDGMENTS
The authors would like to thank Christophe Vignat, Assistant
Professor in Signal Processing, for his contribution to the development
of data processing and to the writing of this manuscript.
BOW-TIE WIDE-BAND MONOPOLE
ANTENNA WITH THE NOVEL
IMPEDANCE-MATCHING TECHNIQUE
Jong-Pil Lee, 1 Seong-Ook Park, 1 and Sang-Keun Lee 2
1 Department of Electronics Engineering Information
and Communications University (ICU)
Taejon, Korea
2 ShinA Info. & Telecomm. Co., Ltd.
Incheon, Korea
Received 12 December 2001
ABSTRACT: A staircase bow-tie monopole-type antenna that features
a novel broadband technique is investigated experimentally and
numerically. A bandwidth of 77.1% (VSWR 2) can be achieved,
and an omnidirectional radiation pattern is obtained. The electrical
characteristics of the proposed antenna make it attractive for use in
multiband mobile systems.© 2002 Wiley Periodicals, Inc. Microwave
Opt Technol Lett 33: 448– 452, 2002; Published online in Wiley Inter-
Science (www.interscience.wiley.com). DOI 10.1002/mop.10347
Key words: wideband monopole; wireless antenna; planar monopole;
slit monopole
1. INTRODUCTION
The design of personal handsets for mobile communication service
has achieved goals such as miniaturization, light weight, and
multiple function. One of the important factors of the handset is the
quality of communication, which is determined by numerous factors.
Among these factors, the antenna that is installed in the
handset and in the base station plays an important part in the
quality of communication. Newer mobile communication systems
require a small, low-priced antenna that has multiple-bandwidth
performance. The microstrip patch antenna is widely employed
because of its planar shape. However, it is a type of resonance
antenna, and its frequency bandwidth is a narrow band of 5%. And
the patch size of the antenna is at least /2, where is the
wavelength of the desired frequency. So it has weaknesses at
low-frequency bands (cellular and GSM bands) in an antenna size.
To overcome these weaknesses, there are the methods of applying
a short pin to a patch antenna [1] and usage of high-dielectric
materials. Here a monopole-type antenna with /4 antenna size is
considered. The conventional monopole and helical structures are
448 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 33, No. 6, June 20 2002

Figure 1
Geometry of a bow-tie-shaped antenna
widely used in mobile handset antennas. The modified type of
antenna, which combines the two types, is used for dual-band
operation [2]. But the modern handset antennas require covert,
low-profile applications. This Letter proposes a novel bow-tieshaped
and printed-type monopole antenna to which the new
method of impedance matching is applied. This method suggests a
slit at the feeding region and an extended ground plane of the
bottom side of antenna. The proposed antenna has a broadband
performance.
2. DESIGN OF ANTENNA
A. Monopole Antenna
The monopole-type antenna has a /4 length physically and a
narrow impedance bandwidth typically. Recently various structures
have been proposed to overcome the narrow-bandwidth
demerits of a monopole.
First, to reduce antenna size, many researchers proposed the
meander line [3]. The meander line is a method by which a length
of antenna is extended electrically; therefore the resonance frequency
of the antenna can be efficiently shrunk. But this method
also has a narrow impedance bandwidth, like a monopole. The
second proposal is to overcome the narrow bandwidth, which is
one of the demerits of the conventional monopole. Parasitic elements
around the monopole antenna bring about various characteristics
[4,5] such as dual band or a multiband operation. But this
idea increases the size of the antenna.
Figure 3 Staircase bow-tie antenna and with the new impedance matching
technique applied
B. Modified Monopole to Achieve Broadband Performance
Rectangular- or elliptical-shaped monopoles were proposed to
overcome the conventional monopole is narrow bandwidth performance
[6,7]. These structures could achieve obtain broadband
applications, but were difficult to apply to mobile communication
handsets. Broadband performance can be obtained by using bowtie-shaped
monopoles [8]. The bow-tie shape has two triangles
facing each other. In this Letter this bow-tie structure is modified
to apply to a handset. One of the two opposite-sided triangles is
cut, and the edge of the remaining one is fed by coplanar
waveguide (CPW) (in Figure 1). The remaining triangle is transformed
into the shape of a staircase bow-tie in order to apply the
new method of impedance matching to the above-mentioned structure,
and the antenna is fabricated by using the printed circuit
board (PCB) (in Figure 3).
First of all, the first mentioned model, a bow-tie-shaped antenna,
is shown in Figure 1. This structure is simulated by Ansoft
Figure 2
Simulated VSWR of a bow-tie-shaped antenna
Figure 4 Simulated results of the proposed model (see Figure 3) [Color
figure can be viewed in the online issue, which is available at www.
interscience.wiley.com.]
MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 33, No. 6, June 20 2002 449

Figure 5 Photograph of the proposed antenna. (a) Top view, (b) bottom view [Color figure can be viewed in the online issue, which is available at
www.interscience.wiley.com.]
HFSS (version 6.0). The result is shown in Figure 2. The simulated
result has 31.4% impedance bandwidth with the frequency range
0.93–1.31 GHz (VSWR 2), and the center frequency of the
return loss is frequency 1.21 GHz. The impedance bandwidth of
the bow-tie-shaped antenna has more wideband characteristics
than the conventional monopole antenna.
C. Application of the New Method for
Wideband Impedance Matching
The new method of impedance matching is applied to a staircase
bow-tie-shaped monopole to get broadband width. As shown in
Figure 3, the new method of impedance matching is that CPW
feeding with a ground plane is extended to the same width as the
antenna at the other side of the antenna, and a slit is made at the
antenna.
The extended ground plane reinforces capacitance. The reinforced
capacitance that results from the extended ground plane
canceled the inductance of an antenna and the extra capacitance of
the extended ground plane is canceled by making a slit in the
antenna.
The results in Figure 4 are simulated, obtained by varying the
length (hg) of the extended ground plane and the depth (hs) of slit.
The center frequency is 1.15 GHz, and the bandwidth for
VSWR 2 is 43.4%, with a frequency range of 0.96–1.4 GHz at
hs 0 mm, hg 0 mm. When the length (hg) of the extended
ground plane is 5 mm and the depth (hs) of the slit is 12 mm, the
center frequency is 1.7 GHz, and the input impedance bandwidth
for VSWR 2 is 63.1% with 1.16–2.23 GHz. Note that the
resonant frequencies and bandwidth are determined by the values
of hg and hs. By adjusting these parameters carefully, it is easy to
optimize the desired frequency band. This case (hg 5 mm, hs
Figure 6 Measured input impedance before application of new impedance
matching technique [Color figure can be viewed in the online issue,
which is available at www.interscience.wiley.com.]
Figure 7 Measured input impedance after application of new impedance
matching technique [Color figure can be viewed in the online issue, which
is available at www.interscience.wiley.com.]
450 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 33, No. 6, June 20 2002

12 mm) is an optimum size to achieve for the maximum frequency
bandwidth. Therefore the effect of the proposed impedance-matching
method to obtain broad bandwidth is remarkable.
Figure 8 Comparison between the before case and the after case [Color
figure can be viewed in the online issue, which is available at www.
interscience.wiley.com.]
3. FABRICATION AND MEASUREMENT
Figure 5 shows the proposed antenna. The substrate used is FR-4,
which is commonly used in printed circuits and is much cheaper
than microwave substrates such as Duroid. The proposed antenna
is fabricated on an FR-4 substrate ( r 4.6). The substrate
thickness is 1.6 mm. Numerous vias connecting the front and back
ground planes are used in the proposed monopole (shown in Figure
5) to suppress spurious parallel plate modes that are known to
occur in the grounded coplanar waveguide.
The VSWR, radiation pattern, and antenna gain were measured.
An HP8722D network analyzer and an HP8510C antenna measurement
system are used. The Smith chart shown in Figure 6 plots
the measured input impedance when the novel impedance matching
technique is not applied. Figure 7 shows the measured input
impedance after application of the new method of impedance
matching. The measured VSWR of two cases (before and after
application) are depicted in Figure 8. The proposed method has
increased the impedance bandwidth from 32.4% (before applica-
Figure 9 Radiation patterns at 1.2 GHz (dotted line, simulated; solid line, measured). (a) xy plane ( 90°), (b) yz plane ( 90°) [Color figure can
be viewed in the online issue, which is available at www.interscience.wiley.com.]
Figure 10 Radiation patterns at 1.7 GHz (dotted line, simulated; solid line, measured). (a) xy plane ( 90°), (b) yz plane ( 90°) [Color figure can
be viewed in the online issue, which is available at www.interscience.wiley.com.]
MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 33, No. 6, June 20 2002 451

tion, 1.02–1.415 GHz) up to 77.1% (after application, 1.03–2.31
GHz).
Figures 9(a) and 9(b) show the radiation patterns at frequencies
of 1.2 GHz of both the measured and simulated results in the xy
and yz planes, respectively. The simulated and measured antenna
gains in the xy plane have a maximum peak at 1.9 and 1.2 dBi,
respectively. Figures 10(a) and 10(b) illustrate the radiation patterns
at frequencies of 1.7 GHz of both the measured and simulated
results in the xy and yz planes, respectively. The simulated and
measured antenna gains in the xy plane have a maximum peak at
2.3 and 1.7 dBi, respectively. This slight discrepancy can be
attributed to the effects of the conductor loss and dielectric loss.
Note that the radiation patterns of the two frequencies (1.2 GHz,
1.7 GHz) have an approximately omnidirectional pattern, similar
to those of a monopole.
4. CONCLUSIONS
It has been demonstrated that a broadband bow-tie monopole type
antenna with the novel impedance-matching technique provided a
wide bandwidth of 77.1% (VSWR 2), and omnidirectional
radiation patterns. Measurements and simulated results were performed,
and it was confirmed that the device could operate as a
maximum bandwidth. The proposed antenna is capable of covering
multiband mobile applications such as DCS, PCS, and IMT-2000.
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© 2002 Wiley Periodicals, Inc.
ANALYSIS OF A CORRUGATED HORN
WITH THE USE OF THE BOR-FDTD
METHOD
Christopher P. Johnson 1 and Parveen Wahid 2
1 Harris Corporation
2400 Palm Bay Road
Palm Bay Florida 32905
2 School of Electrical Engineering and Computer Science
University of Central Florida
Orlando Florida 32816
Received 14 December 2001
ABSTRACT: The derivation of the body-of-revolution finite-difference–
time-domain (BOR-FDTD) technique is presented and used to determine
the return loss and radiation patterns of a corrugated horn. The perfectly
matched layer (PML) absorbing boundary conditions are used for
the computation. The source excitation is a sine-modulated Gaussian
pulse, spatially weighted with the cylindrical TE 11 mode fields. The results
for the return loss and radiation patterns are compared with
those obtained using a commercial package based on a modematching/method-of-moments
technique. The results show excellent
agreement. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett
33: 452–457, 2002; Published online in Wiley InterScience (www.
interscience.wiley.com). DOI 10.1002/mop.10348
Key words: BOR-FDTD; corrugated horn; mode-matching; method of
moments
INTRODUCTION
BOR-FDTD codes have been used for many years in the particle
physics, optics, and electromagnetic communities. They have been
used in various applications such as the modeling of wake-field
phenomena in particle accelerators [1], wave propagation through
optical lenses [2], resonant cavities [3], and simple coaxially fed
antennas [4], among others. In this Letter the BOR-FDTD method
is used to determine the return loss and radiation patterns of a
corrugated horn.
The first section provides the derivation of the BOR-FDTD
equations. The boundary conditions are then given for components
lying on the z axis, followed by the equations for the perfectly
matched layer absorbing boundary conditions. Next, a method of
waveguide source excitation is given. And finally, modeling results
are shown for a load-terminated waveguide and a corrugated
horn radiating into free space.
BOR-FDTD FORMULATION
Many practical antennas, including corrugated horns, contain rotational
symmetry and are termed bodies of revolution (BOR). In
this Letter a BOR-FDTD formulation is presented for application
to BOR structures containing both conducting surfaces and dielectrics.
Only materials that are linear, isotropic, and nondispersive
are considered. The possibility of lossy materials is considered by
defining equivalent magnetic and electric currents. Hence, the
derivation begins with Maxwell’s curl equations written in the
following differential form:
E H
*H, (1)
t
H E
E, (2)
t
452 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 33, No. 6, June 20 2002