IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 51, NO. 6, JUNE 2003
Fig. 3(a) displays the measured return loss characteristic for the
x-cut version of the LiNbO3 hi-lo antenna. A measured bandwidth
of 9.2% centered at approximately 12.8 GHz was observed, which
is slightly lower than the z -cut antenna, but still adequate for most
wireless communication systems.
The far field radiation patterns at 12.75 GHz for the x-cut LiNbO3
hi-lo antenna are given in Fig. 3(b). As the LiNbO3 wafer and the brass
mounting block were approximately the same dimensions as in the
z -cut case, the slight ripple in the patterns is still evident. The F/B ratio
was measured to be approximately 26 dB, and a wide 3 dB beamwidth
is again observed. The cross-polarization level in each plane of the
x-cut LiNbO3 hi-lo stacked patch was more than 30 dB below the
copolarization level at broadside. The gain of the x-cut LiNbO3 hi-lo
antenna was approximately 7 dBi. The computed gain differed by less
than 1 dB from the directivity for both of the LiNbO3 antenna structures, illustrating the efficiency of the hi-lo architecture, and implying
low surface wave activity.
IV. CONCLUSION
Two hi-lo stacked patch antenna structures have been constructed
employing z -cut/x-cut LiNbO3 wafers and a low permittivity foam dielectric. The use of the LiNbO3 material enables the full integration
of the antenna with electro-optic photonic devices. This can reduce the
size, complexity and cost of base stations or remote antenna units in
applications such as hybrid fiber-radio systems at high microwave and
millimeter-wave frequencies. The LiNbO3 hi-lo configuration yields
very good impedance and radiation characteristics. The simple nature
of the hi-lo structure is compliant with the package requirements for
OEICs, facilitating the realization of combined antenna/photonic/ microwave modules.
ACKNOWLEDGMENT
The authors would like to thank Y. Visagathilagar, C. P. Wu, and S.
Donovan for their assistance in the processing of the LiNbO3 wafers,
and D. Welch for the mounting structures.
REFERENCES
[1] Y. Furuhama, “Research and developments of millimeter-wave technologies for advanced communications,” in Proc. 3rd RIEC Symp.
Novel Techniques and Applications Millimeter-Waves, Sendai, Japan,
Dec. 1998, pp. 1–6.
[2] T. Nagatsuma, A. Hirata, Y. Royter, M. Shinagawa, T. Furuta, T.
Ishibashi, and H. Ito, “A 120-GHz integrated photonic transmitter,” in
Proc. Int. Topical Meeting Microwave Photonics (MWP 2000), Oxford,
U.K., Sept. 2000, pp. 225–228.
[3] K. Takahata, Y. Muramoto, S. Fukushima, T. Furuta, and H. Ito, “Monolithically integrated millimeter-wave photonic emitter for 60-GHz fiberradio applications,” in Proc. Int. Topical Meeting Microwave Photonics
(MWP 2000), Oxford, U.K., Sept. 2000, pp. 229–232.
[4] D. Mirshekar-Syahkal and D. Wake, “Bow-tie antennas on high dielectric substrates for MMIC and OEIC applications at millimeter-wave frequencies,” Electron. Lett., vol. 31, no. 24, pp. 2060–2061, Nov. 1995.
[5] J. S. Colburn and Y. Rahmat-Samii, “Patch antennas on externally perforated high dielectric constant substrates,” IEEE Trans. Antennas Propagat., vol. 47, pp. 1785–1794, Dec. 1999.
[6] W. S. T. Rowe, R. B. Waterhouse, A. Nirmalathas, and D. Novak, “Integrated antenna base station design for hybrid fiber radio networks,” in
Proc. Int. Topical Meeting Microwave Photonics, Melbourne, Australia,
Nov. 1999, pp. 47–50.
[7] G. Lefort and T. Razban, “Microstrip antennas printed on lithium niobate
substrate,” Electron. Lett., vol. 33, no. 9, pp. 726–727, Apr. 1997.
1415
[8] T.-H Lin, “Via-free broadband microstrip to CPW transition,” Electron.
Lett., vol. 37, no. 15, pp. 960–961, July 2001.
[9] W. S. T. Rowe and R. B. Waterhouse, “Broadband microstrip patch antennas for MMIC’s,” Electron. Lett., vol. 36, no. 7, pp. 597–599, Mar.
2000.
The Low-Profile Hemispherical Helical Antenna With
Circular Polarization Radiation Over a Wide
Angular Range
H. T. Hui, K. Y. Chan, and E. K. N. Yung
Abstract—The low-profile hemispherical helical antenna is studied experimentally and theoretically. This antenna can produce circular polarization radiation over a wide angular range of 90 . The current distribution, the input impedance, the axial ratio, the power gain, and the radiation pattern are rigorously studied. The 3-dB axial ratio bandwidth of a
five-turn hemispherical helical antenna is found to be 14.6. In the range of
10
1 3, a relatively stable power gain of more than 9 dB is
obtained. The radiation patterns typically consist of a large smooth main
lobe with almost no sidelobes. These new antenna characteristics have a
potential application in mobile satellite communications.
Index Terms—Circular polarization radiation, hemispherical helical antenna, satellite communications.
I. INTRODUCTION
Antennas with circular polarization radiation have found wide applications in mobile satellite communications and direct satellite broadcasting systems due to their insensitivity to the ionospheric polarization
rotation. Conventional long cylindrical helical antennas can produce
circular polarization radiation but only within a small angular range in
the axial direction [1], [2]. In [3], Nakano et al. introduced a small and
very low-profile cylindrical helical antenna which produces very pure
circular polarization radiation over a broader angular range. A quadrifilar helix antenna [4] can produce circular polarization radiation over
the whole upper half space but it exhibits narrow-bandwidth and requires a complicated feeding method. A spherical helical antenna [5]
can produce circular polarization radiation over a wide angular region
but it is difficult to maintain in a stable vertical position over the ground
plane. In this paper, we report an intensive study of the hemispherical
helical antenna proposed by Hui et al. [6]. The hemispherical helical
antenna, unlike the spherical helical antenna, is not only smaller in size,
but also provides a more robust and low-profile structure. It can produce circular polarization radiation over a wide angular range with a
relatively high gain. The current distribution, the input impedance, the
axial ratio, the power gain, and the radiation patterns are rigorously
investigated. The antenna size of the hemispherical helical antenna is
fixed irrespective of the number of turns of the helix. This leads to some
antenna characteristics such as the power gain and the radiation pattern
remaining relatively unchanged with the number of turns of the helix
Manuscript received November 22, 2000; revised April 15, 2002.
H. T. Hui is with the School of Electrical and Electronic Engineering,
Division of Communication Engineering, Nanyang Technological University,
639798 Singapore.
K. Y. Chan and E. K. N. Yung are with the City University of Hong Kong,
Hong Kong.
Digital Object Identifier 10.1109/TAP.2003.812187
0018-926X/03$17.00 © 2003 IEEE
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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 51, NO. 6, JUNE 2003
Fig. 1. Antenna geometry of the peripheral-feed hemispherical helical
antenna.
while other characteristics such as the axial ratio and the current distribution being easily changed by the number of turns of the helix. Both
theoretical and experimental results will be presented.
II. GEOMETRICAL DESCRIPTION
The antenna geometry of the coaxially fed hemispherical helical antenna with an equal spacing between adjacent turns is shown in Fig. 1.
The thin helical wire is wound on a hemispherical surface. The coordinates along the axis of the helical wire satisfy the following equation
in spherical coordinates:
r = a;
= cos01
6
2N
01
;
2N
4N
(1)
Fig. 2. Measured axial ratio of a three-turn hemispherical helical antenna with
= 1 2, = 1.95 cm, = 0.8 cm,
=
the elevation angle for
0.05 cm, and = 4 5 .
TABLE I
3-dB AXIAL-RATIO BANDWIDTHS OF THE HEMISPHERICAL HELICAL ANTENNA
WITH DIFFERENT NUMBER OF TURNS OF THE HELIX. THE DIMENSIONS OF THE
= 0.05 cm, AND = 4 5
ANTENNA ARE = 1.95 cm, = 0.5 cm,
where a is the radius of the hemisphere and N is the number of turns
of the helix. The “+” or “0” sign in (1) indicates that the equation
is for a right-handed (“+”) or a left-handed (“0”) helix. Only hemispherical helixes with an integral number of turns will be investigated
in this study. The length of the short straight wire joining the helix to
the coaxial line on the ground plane is denoted by h. The whole antenna
is made of a single thin wire of uniform radius rw . The coaxial aperture
has an inner radius rw and an outer radius b. In the experimental measurements, the hemispherical helix was wound by using a copper wire
on the surface of a polystyrene hemisphere, which enables the antenna
to rest stably on the ground plane. The ground plane is a square copper
plate with a side length of 20 cm, which is equal to 1.96 wavelengths at
a frequency of 2.94 GHz. Theoretical analysis of the antenna is carried
out by using moment method [7].
III. THEORETICAL AND MEASUREMENT RESULTS
A. Axial Ratio and Power Gain
Fig. 2 shows the measured axial ratio of a three-turn hemispherical
helical antenna with the elevation angle at a normalized circumference of C= = 1.2 (where C is the circumference of hemispherical
helix and is the wavelength) and with a = 1.95 cm, h = 0.5 cm,
rw = 0.05cm, and b = 4:5rw . It can be seen that the angular coverage with circular polarization radiation (axial ratio 3 dB) is about
90 (040 50 ). The variation of the axial ratio and power gain
with C= and with the number of turns N is shown in Fig. 3. It is found
that an increase in the number of turns of the helix can reduce the axial
ratio. The 3-dB axial-ratio bandwidths (axial ratio 3 dB) are shown
in Table I. The 3-dB axial ratio bandwidth increases with the number
of turns. The bandwidth of the five-turn antenna is almost double that
of the three-turn antenna. The power gain shown in Fig. 3 is defined
with respect to an isotropic circularly polarized source. We see that the
power gain remains relatively stable with the number of turns and with
C= for 1:0 C= 1.3. The power gain in this range varies from
9.1–9.8 dB. This characteristic is very different from the behavior of
Fig. 3. Variation of the axial ratio and power gain of the hemispherical helical
antenna with
and with the number of turns
for
=1.95 cm, =
0.5 cm,
= 0.05 cm, and = 4 5 .
the power gain of a cylindrical helical antenna which increases significantly with the number of turns and with frequency [1].
A comparison of the cross- and the co-polarization radiation patterns
of a five-turn hemispherical helical antenna with those of a two-turn
IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 51, NO. 6, JUNE 2003
1417
Fig. 4. Variations of the cross- and co-polarization with the elevation angle of a five-turn hemispherical helical antenna compared with a two-turn low-profile
cylindrical helical antenna over different -planes. The dimensions of the hemispherical helical antenna are
= 1.23, = 0.5 cm, = 1.95 cm,
=
0.05 cm, and = 4 5 , and the dimensions of the cylindrical helical antenna are
= 0.4 cm, = 4 ,
= 1.0, = 0.125 cm,
= 0.05 cm,
and = 4 5 .
low-profile cylindrical helical antennas studied by Nakano et al. [8] is
shown in Fig. 4 over different -planes. The dimensions of the hemispherical helical antenna are C= = 1.23, h = 0.5 cm, a = 1.95 cm,
rw = 0.05 cm, and b = 4:5rw . The dimensions of the two-turn cylindrical helical antenna are aH = 0.4 cm, = 4 , CH = = 1.0, h =
0.125 cm, rw = 0.05 cm, and b = 4:5rw , where aH is the radius,
is the pitch angle, and CH is the circumference of the cylindrical
helix. We observe from Fig. 4 that although the angular ranges of circular polarization are similar for the two antennas, the purity of circular
polarization radiation of the hemispherical helical antenna is, in general, higher in the axial direction (about 5 dB better within the range of
015 15 ).
B. Current Distribution and Input Impedance
The current distribution largely determines the operation of a wire
antenna [9]. In Fig. 5, the current distributions of a five-turn hemispherical helical antenna at three normalized circumferences of C= = 1.1,
C= = 1.23, and C= = 1.3 are shown (the magnitude distributions).
The wire lengths for these three cases are, respectively, 4.4, 4.93,
and 5.2. It can be seen that except for the case with C= = 1.23, the
current distributions of the other two cases show the existence of a reflected current wave traveling backwards from the open end towards
the feed point. The reflected current wave will produce circular polarization radiation in the opposite sense from that produced by the forward traveling current wave and hence damages the purity of circular
polarization radiation produced by the forward traveling current wave.
Thus, the axial ratios for these two cases are 3 dB for C= = 1.1 and
4.9 dB for C= = 1.3. For the case with C= = 1.23, the wire length
Fig. 5. Current distribution of a five-turn hemispherical helical antenna at three
ratios for = 1.95 cm, = 0.5 cm,
= 0.05 cm, and = 4 5 .
is approximately five wavelengths and a smoothly decaying traveling
current wave along the antenna wire can be seen. This satisfies the two
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IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 51, NO. 6, JUNE 2003
diation. The current distribution, the input impedance, the axial ratio,
the radiation pattern, and the power gain are rigorously studied. A 14.6
% 3-dB axial ratio bandwidth is obtained with a five-turn antenna. The
power gain remains relatively stable with the number of turns of the
helix and with frequency. The radiation patterns typically consist of a
large smooth main lobe with almost no sidelobes.
REFERENCES
Fig. 6. Input impedance of a five-turn hemispherical helical antenna with
0.5 cm, = 1.95 cm,
= 0.05 cm, and = 4 5 .
=
Fig. 7. Radiation patterns of a five-turn hemispherical helical antenna over the
plane with = 0 and 180 and the dimensions are
= 1.14, = 1.95
cm, = 0.5 cm,
= 0.05 cm, and = 4 5 .
[1] J. D. Kraus, Antennas. New York: McGraw-Hill, 1988.
[2] H. E. King and J. L. Wong, “Characteristics of 1 to 8 wavelength uniform
helical antennas ,” IEEE Trans. Antennas Propagat., vol. AP-28, pp.
291–296, Mar. 1980.
[3] H. Nakano, H. Takeda, T. Honma, H. Mimaki, and J. Yamauchi, “Extremely low-profile helix radiating a circularly polarized wave ,” IEEE
Trans. Antennas Propagat., vol. 39, pp. 754–757, June 1991.
[4] J. M. Tranquilla and S. R. Best, “A study of the quadrifilar helix antenna for Global Positioning System applications,” IEEE Trans. Antennas Propagat., vol. 38, pp. 1545–1550, Oct. 1990.
[5] J. C. Cardoso and A. Safaai-Jazi, “Spherical helical antenna with a
circular polarization over a broad beam,” Electron. Lett., vol. 29, pp.
325–326, 1993.
[6] H. T. Hui, K. Y. Chan, E. K. N. Yung, and X. Q. Sheng, “The coaxial-feed
axial mode hemispherical helical antenna,” Electron. Lett., vol. 35, pp.
1982–1983, 1999.
[7] R. F. Harrington, Field Computation by Moment Methods. New York:
IEEE Press, 1993.
[8] H. Nakano, H. Takeda, Y. Kitamura, H. Mimaki, and J. Yamauchi, “Lowprofile helical array antenna fed from a radial waveguide,” IEEE Trans.
Antennas Propagat., vol. 40, pp. 279–284, Mar. 1992.
[9] H. Nakano, S. Okuzawa, K. Ohishi, H. Mimaki, and J. Yamauchi, “A
curl antenna,” IEEE Trans. Antennas Propagat., vol. 41, pp. 1570–1575,
Nov. 1993.
Comprehensive Analysis and Simulation of a 1–18 GHz
Broadband Parabolic Reflector Horn Antenna System
Christian Bruns, Pascal Leuchtmann, and Rüdiger Vahldieck
conditions for circular polarization radiation produced by a wire antenna [9] and a very low axial ratio of 0.5 dB is obtained.
Fig. 6 shows the measured and calculated input impedance of
a five-turn antenna with C=. It can be seen that within the 3-dB
axial-ratio bandwidth (C= = 1.1 to 1.28), the input resistance
(measured) varies from 175 to 75 while the input reactance
(measured) changes from -160
to -80
. We further found that when
the number of turns of the hemispherical helix increases, the input
impedance changes more rapidly with C=.
C. Radiation Pattern
The calculated and measured radiation patterns of a five-turn hemispherical helical antenna are shown in Fig. 7 over the plane with = 0
and 180 . The radiation patterns consist of a large main lobe with almost no sidelobes. This characteristic persists over a wide C= range
from C= = 1.1 to C= = 1.5 and over the number of turns of the
helix from N = 3 to N = 8. The half-power beamwidths are measured to be 71 for E and 85 for E .
Abstract—A 1–18 GHz parabolic reflector horn antenna system featuring a broadband double ridged primary horn with a coaxial feed line
is investigated. For the ridged horn antenna it is found that the radiation
pattern, contrary to common believe, does not maintain a single main lobe
in the direction of the horn axis over the whole frequency range. Instead,
at frequencies above 12 GHz the main lobe in the radiation pattern starts
to split into four lobes pointing in off-axis directions with a dip of up to 6
dB between them along the center axis. To investigate this phenomenon in
detail, a combined method of moments and physical optics approach has
been adopted to simulate the complete antenna system.
Index Terms—Broadband ridged horn antenna, method of moments
(MoM), parabolic reflector, physical optics (PO), radiation pattern
deterioration.
I. INTRODUCTION
Horn antennas are widely used devices in applications such as standard measurement equipment, electromagnetic compatibility (EMC)
testing, radar, and communication systems. Generally they are simple
IV. CONCLUSION
The hemispherical helical antenna is rigorously studied both theoretically and experimentally. This antenna provides a robust and low-profile structure with a wide angular coverage of circular polarization ra-
Manuscript received January 26, 2001; revised November 19, 2001.
The aüthors are with the nstitut für Feldtheorie und Höchstfrequenztechnik,
ETH Zurich, Zurich 8092 Switzerland (e-mail: [email protected]).
Digital Object Identifier 10.1109/TAP.2003.812236
0018-926X/03$17.00 © 2003 IEEE