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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 53, NO. 10, OCTOBER 2005 3403
An Ultrawide-Band Double Discone Antenna With the
Tapered Cylindrical Wires
Ki-Hak Kim, Jin-U Kim, and Seong-Ook Park
Abstract—A novel double discone antenna is composed of the asymmetric
biconical antenna and upside-down discone antenna. The asymmetric
biconical antenna has all-wire structure like octopus legs for covering
at lower operating frequency, and the upside-down discone antenna has
conical shape playing a role as covering at higher operating frequency.
An elaborate assembly of two antenna exhibits a 1:100 impedance bandwidth
(180 MHz–18 GHz) with VSWR below 2.5 while maintaining an
acceptable omnidirectional radiation pattern except at about 12 GHz
region. The simulated performances of the proposed antenna are verified
by the measured results of the fabricated antenna. There seems to be good
agreement with each other. These features make such antennas highly
suitable for application to UWB system.
Index Terms—Asymmetric biconical antenna, double discone antenna.
I. INTRODUCTION
The development of the ultrawide-band (UWB) system has brought
about rapid growth of broad band antenna techniques. Since UWB
antennas have typically been designed with specifications that include
constant gain and linear phase response, it is necessary to modify the
existing antenna model or develop a new wide band antenna. Among
existing UWB antennas such as biconical, discone, double-ridged
waveguide horn, and log-periodic antenna, the discone antenna is typical
antennas used for UWB systems. First, the biconical antenna has
good performance if the dimension is infinite, but practical antennas
should be finite structure. The general dimension of the biconical
antenna is about a half wavelength of cutoff frequency, so it has disadvantages
in terms of size. Second, the double-ridged waveguide horn
and log-periodic antenna have a directional radiation pattern. Finally,
even though the discone antenna has an omnidirectional radiation
patternand relatively small size, its radiationpatternis tilted down
due to the asymmetric structure [1]–[4] and [8].
Therefore, this paper describes and analyzes the novel ultrawide-band
double discone antenna for UWB systems. The antenna
presented in this paper is a combination of the asymmetric biconical
and upside-down discone antennas. The proposed antenna has a
structure of radial wires to reduce weight and wind resistance. The
performances of the proposed antenna are similar to those of the
discone antenna even though it is constructed like the asymmetric
biconical antenna. The upside-down discone is used for higher sections
above 1.5 GHz [1]. This upside-down discone is similar to
conical antennas mounted on the finite ground plane [2]. The upper
radial wires of the proposed antenna have a long tapered cylindrical
shape to obtain better performance of VSWR. The antenna is coupled
with a feed coaxial waveguide, where only the TEM mode is
excited. As a result, the proposed antenna exhibits broader impedance
bandwidth. In this paper, details of the antenna design are described,
and the simulated and measured results are presented to show the
validity of the proposed antenna. To understand the behavior of the
Manuscript received November 4, 2004; revised April 28, 2005. This work
was supported by the Ministry of National Defense, Republic of Korea, Dual
Use Technology Program under Contract 2EN0300.
The authors are with the School of Engineering, Information and Communications
University, Daejeon 305-732, Korea (e-mail: kkh8166@icu.ac.kr;
jinu@icu.ac.kr; sopark@icu.ac.kr).
Digital Object Identifier 10.1109/TAP.2005.856036
Fig. 1. Configuration of the proposed antenna. (a) Asymmetric biconical
antenna, (b) upside-down discone antenna, and (c) the proposed antenna:
combined structures with (a) and (b).
antenna model and obtain the optimum parameters, the simulation
was performed with CST MICROWAVE STUDIO based onthe finite
integration method [5]. The measurement was carried out using the
Agilent 8510C Network Analyer.
II. ANTENNA CONFIGURATION
Fig. 1 shows the proposed antenna structure. The total size of this
antenna is 370 mm 2 400 mm, and the dimensions were optimized
to obtain much broader bandwidth. The antenna is constructed as
shown in Fig. 1 with a combination of the asymmetric biconical
and the upside-down discone antenna. The lower radial wires play
a role as ground plane and affect the antenna’s bandwidth and
radiation pattern. The number of the lower radial wires is twelve.
In order to place the upside-down discone antenna, the upside-down
discone with four bore holes is connected to the four dielectric
posts with a diameter of 5.9 mm, as showninFig. 2. The four
dielectric posts are made from polycarbon ("r =2:9). The four
dielectric posts are bridged between the upside-down discone and
the upper flat regionof the lower radial wires. The presence of the
dielectric obstacle near and at the feeding region can significantly
affect antenna performances [6]. Therefore, the distance between
the dielectric post and the center of the feeding point is 30.45 mm
as shown in Fig. 2(c). This distance has negligible influence on
0018-926X/$20.00 © 2005 IEEE

3404 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 53, NO. 10, OCTOBER 2005
TABLE I
DESIGN PARAMETERS OF THE PROPOSED ANTENNA
Fig. 3. Experimented antenna configuration. (a) Disk plate, (b) uniform
cylindrical wires, and (c) tapered cylindrical wires (proposed antenna).
Fig. 2. Feeding structure of the proposed antenna. (a) Photograph of the
antenna, (b) enlarged drawing of the feeding structure, and (c) top view of
Fig. 2(b).
antenna characteristics. Fig. 2(b) shows a feeding structure in which
the inner conductor of the N-type jack connector is attached to and
penetrates into the center of the upside-down discone. Finally, the
feeding structure is fixed firmly with dielectric posts and an N-type
jack connector. Fig. 1(b) shows the structure of an upside-down
discone. The height h, angle 2 , and width w of the upside-down
discone are optimized to maximize the bandwidth ratio and gain.
Input impedances of the proposed antenna are governed by the
half-cone angle 2 of the upside-downdiscone [3]. The upper flat
regionof the lower radial wires and the disk of the upside-down
discone have the same width with the dimension of w =70mm.
The upper radial wires (twelve wires) influence bandwidth, gain, and
radiation patterns [7]. In order to obtain good performances as well
as reduce antenna size, the angle 1 was optimized to 20 degrees
inFig. 1(c). The tapered cylindrical wires are modified from the
conventional discone antenna’s disk [1]. The tapered cylindrical
wires allow the input impedance to have a broader bandwidth. If
a disk plate is used in the proposed antenna instead of the upper
radial wires, the performances of the antenna are not good due to
the coupling effect or the reflected wave between the upside-down
discone and disk plate, as shown in Fig. 4. In this structure, the
ultrawide bandwidth can be achieved by properly choosing a location
of the four dielectric posts, , and 1 of the antenna. Furthermore, by
continuously adjusing the height h and angle 2 of the upside-down
discone, it is possible to tune the impedance matching level. As a
result, the modified antenna has an upside-down discone and tapered
cylindrical wires. This results in a broader VSWR than that of the
conventional UWB antennas. The associated antenna parameters for
achieving optimum performance are given in Table I.
Fig. 4. Comparisons of the measured VSWR among the antennas having disk
plate, uniform cylindrical wires, and tapered cylindrical wires, respectively.
Fig. 5. Comparisons of the measured and simulated VSWR for the proposed
antenna.
III. RESULTS
A. VSWR
Fig. 4 shows the results of VSWR among tapered cylindrical wires,
uniform cylindrical wires, and the disk plate, respectively. As seen
in Fig. 4, the dashed line, thin solid line, and thick solid line denote
the VSWR values of Fig. 3(a), Fig. 3(b), and Fig. 3(c), respectively.

IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 53, NO. 10, OCTOBER 2005 3405
Fig. 7.
Measured and simulated antenna gains.
TABLE II
ANGLES OF THE MEASURED MAXIMUM GAIN IN FIG. 6
uniform cylindrical wires in Fig. 3(b) does not satisfy VSWR < 2:5
in the vicinity of 13 GHz and 18 GHz. The antenna of Fig. 3(a) only
satisfies bandwidth up to 4.3 GHz.
The measured and simulated VSWR of the proposed antenna are
showninFig. 5. As showninFig. 5, the simulated and measured VSWR
patterns seem to be in good agreement with each other. However, there
are slight discrepancies between these results, due to mechanical inaccuracies
and feeding problems from the jack adaptor, which were not
considered in the simulation. From these results, it can be demonstrated
that the proposed antenna has a broader VSWR over 100 to 1 bandwidth
without using the impedance matching tuner.
Fig. 6. Simulated and measured E-plane radiation patterns: (a) 0.5 GHz,
(b) 0.7 GHz, (c) 1 GHz, (d) 2 GHz, (e) 3 GHz, (f) 4 GHz, (g) 8 GHz, (h) 12 GHz,
(i) 15 GHz, and (j) 18 GHz ( measured results; ......simulated results).
The measured VSWRs of the proposed antenna in Fig. 3(c) have
180 MHz18 GHz (VSWR < 2:5). However, the antenna having
B. Radiation Patterns and Gains
The measured and simulated radiation patterns of the proposed antenna
in E-planes are shown in Fig. 6. The measured and simulated
results agree well with each other. As showninFig. 6, the radiation
patterns at low frequencies are similar to those of the short dipole. As
the operating frequency increases up to higher frequencies, the patterns
are tilted downward because the upper radial wires and lower radial
wires are an asymmetric structure [7]. However, the downward tilting
phenomenon above 2 GHz is not occured. The proposed antenna offers
satisfactory radiation performance while retaining the omnidirectional
pattern. However, it is clearly observed that the null phenomenon at
angle occurs at 12 GHz in Fig. 6(h). Except for the 12 GHz region, the
omnidirectional pattern of this antenna is maintained.
The measured and simulated gains are shown in Fig. 7. A threeantenna
technique is used to measure the radiation gain. The gain value
has beentakenat angle where the gainis the maximum. Each associated
tilted angle at all frequencies is listed in Table II. The measured gain
error is within 60.5 dBi accuracy. The measured gainabove 1 GHz frequency
range has an average 3 dBi or more. The discrepancies between
the simulated and measured gains can be attributed to the antenna loss
effects and the uncertainty of the simulated results. However, the simulated
and measured gains have a similar tendency.

3406 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 53, NO. 10, OCTOBER 2005
IV. CONCLUSION
This paper demonstrates a double discone antenna for the UWB
system which is a combination of the asymmetric biconical and upside-down
discone structures. In order to improve VSWR performance,
a tapered cylindrical wire at an angle of 20 was proposed instead of
the disk plate and uniform cylindrical wires. Additionally, four dielectric
posts were employed to place the upside-down discone and lower
radial wires firmly. The performances were verified by the measured
and simulated results of the fabricated prototype antenna. This antenna
exhibited an omnidiectional radiation pattern and relatively small size
while retaining 100:1 impedance bandwidth. The proposed double discone
antenna with tapered cylindrical wires has a wider bandwidth performance,
when compared to that of any existing conventional UWB
antennas. These features make the proposed antenna very suitable for
UWB system antennas and radio frequency monitoring.
ACKNOWLEDGMENT
The authors would like to thank the two anonymous reviewers for
their comments which improved this paper.
REFERENCES
[1] J. U. Kim and S. O. Park, “Novel ultra-wideband discone antenna,” Microw.
Opt. Technol. Lett., vol. 42, pp. 113–115, Jul. 2004.
[2] G. Liu and C. A. Grimes, “Spherical-coordinate FDTD analysis of conical
antennas mounted above finite ground plane,” Microw. Opt. Technol.
Lett., vol. 23, pp. 78–82, Oct. 1999.
[3] J. D. Kraus, Antennas, 2nd ed. New York: McGraw-Hill, 1998, pp.
692–694.
[4] T. Taniguchi and T. Kobayashi, “An omnidirectional and low-VSWR
antenna for the FCC-approved UWB frequency band,” in Proc. IEEE
Antennas Propagat. Symp., Jun. 2003, pp. 460–463.
[5] “Computer SimulationTechnology (CST) Microwave Studio,” ver. 4.2
Available: www.cst.com.
[6] R. Stovall and K. Mei, “Application of a unimoment technique to a biconical
antenna with inhomogeneous dielectric loading,” IEEE Trans.
Antennas Propag., vol. 23, no. 3, pp. 335–342, May 1975.
[7] K. Nagasawa and I. Matsuzuka, “Radiation field consideration of biconical
horn antenna with different flare angles,” IEEE Trans. Antennas
Propag., vol. 36, no. 9, pp. 1306–1310, Sep. 1988.
[8] J. R. Bergmann, “On the design of broadband omnidirectional compact
antennas,” Microw. Opt. Technol. Lett., vol. 39, pp. 418–422, Dec. 2003.
Beam Focusing Properties of Circular Monopole Array
Antenna on a Finite Ground Plane
Satish Kumar Sharma and Lotfollah Shafai
Abstract—This paper presents the investigation results on the beam focusing
properties of a wire circular monopole array (CMA) antenna consisting
of six-elements on a finite ground plane, by exciting more than one
monopole at a time. The excitation of more than one element provides enhanced
horizontal and vertical plane peak directivities, and a reduced 3 dB
beamwidth for the horizontal pattern. The effect of varying the number of
monopole elements in the array is also discussed, when only one element
is excited, and the remaining ones are shorted to the ground. The antenna
was fabricated and tested for its impedance and radiation characteristics
for one of the excitation schemes, and the results were found in reasonable
agreement with the simulations.
Index Terms—Beam focusing properties, circular monopole array
(CMA), finite ground, multiple excitations.
I. INTRODUCTION
Monopole antennas are widely used in mobile wireless communications,
because of their simplicity and broad-band characteristics
[1], [2]. In terrestrial multipath loss environments, the horizontal
plane sector beams need narrow beamwidths, so that least inter-sector
interference is present [3]. One way to generate the narrow beam is
to excite one element of a circular array (Fig. 1), while keeping the
remaining ones passive to behave as a reflector [4]. This is similar
to the corner reflectors, where by adjusting the angle between the
corners, the beamwidth and directivity can be controlled [3]. In [5],
[6], electronically steerable switched parasitic arrays, for the base-station
tracking in mobile communications, employing a directional
array with only one active element and three parasitic elements were
presented. In [7], authors presented a historical survey of switched
parasitic antennas and various ways of generating switched beams by
employing different number of wire elements in the arrays. In [8],
authors presented a six-element circular switched monopole array on
an infinite ground plane for beam steering in the azimuth or horizontal
plane. It provided a directivity of 10.8 dBi at the beam peak by exciting
two elements simultaneously, while shorting the remaining ones to
the ground. In [9], a seven-element electrically steerable passive array
radiator (ESPAR) was designed to enhance its horizontal gain by using
a skirt on a circular ground plane, which showed a gain of 8.00 dBi in
both E- and H-planes. In [10], [11], a few initial investigation results,
on the antenna discussed in this paper, were presented.
Incertainapplications directive beams are required inboth elevation
and horizontal planes, with different beam characteristics. The L-band
digital radio broadcast (DRB) is one such case, simultaneously broadcast
from a geostationary satellite and ground stations. A mobile vehicle
may access either, depending on the signal strength. However, the
satellite elevation angles depend on the geographical location, and for
southern regions of Canada, the elevation angles between 30 to 40
are the most likely satellite directions, where the mobile antenna must
be aimed. On the other hand, for the terrestrial stations, both mobile
and the transmitter antennas are in the horizontal plane, where the antenna
gain, and the front-to-back (F/B) ratio, must be sufficient to allow
signal reception and discrimination in the multipath loss environment.
0018-926X/$20.00 © 2005 IEEE
Manuscript received November 27, 2003; revised April 22, 2005.
The authors are with the Department of Electrical and Computer Engineering,
The University of Manitoba, Winnipeg, Manitoba R3T 5V6, Canada (e-mail:
sharma@ee.umanitoba.ca; shafai@ee.umanitoba.ca).
Digital Object Identifier 10.1109/TAP.2005.856376