Novel wide-band low-cost antenna for mobile communication system

Abstract

This paper presents a novel wideband low-cost antenna which covers the frequency band from 1.15GHz to 3.7GHz, so it can be used in the wireless communication systems of GSM-1800, PCS, IMT2000, WCDMA, WLAN, OFDM, MIMO and B3G. In 3.5GHz band it can be used in broadband wireless access of point-to-point and point-to-multipoint. The structure of the antenna is simple and so it can be mass produced easily and cheaply. Therefore, it could be applied to ceiling antennas, wall antennas, vehicle carried antennas and as the basic element of antenna arrays for base stations.

Full text

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Novel Wide-Band Low-Cost Antenna for
Mobile Communication System

Wei Jiang, Yinchun Liu, Xiaowei Zhu, and Wei Hong Member, IEEE,
State Key Lab. of Millimeter Waves,
Department of Radio Engineering, Southeast University,
Nanjing, 210096, P. R. China


INTRODUCTION

Recently, the operation frequency band of many mobile communication systems on
service or under development is crowded around 1.9GHz, 2.1GHz, 2.4GHz and 3.5GHz.
It can be seen the situation of multiple mobile communication systems simultaneous
operation and exist in the future. To develop a wide-band and simple configuration
antenna compatible multiple mobile communication systems is the best choice.
The monopole antenna with simple configuration, easy feed and small transverse
dimension has widely used in engineering. Whereas, it is not easy to get impedance
match for a monopole antenna and then its operation bandwidth is not wide enough for
multi-band purpose, so it can’t meet the requirement of modern wide-band, huge capacity
communication. Early in 60 years ago, the experiment proved the wide bandwidth and
favorable match of antenna could be realized by placing a coaxial metal pipe connected
to ground outside the normal monopole antenna. And it also achieve satisfied radiation
direction pattern [1]. Wang put a couple of parasitic dipoles for updating the radiation
performance [2].
This paper presents a novel wide-band low-cost antenna which covers frequency band
from 1.15GHz to 3.7GHz, so it can be used in the wireless communication systems of
GSM-1800, PCS, IMT2000, WCDMA, WLAN, OFDM, MIMO and B3G. In 3.5GHz
band it can be used in broadband wireless access of point-to-point and point-to-multipoint.
The structure of the antenna is simple and so it can be mass produced easily and cheaply.
Therefore, it could be applied to ceiling antenna, wall antenna, vehicle carried antenna
and as the basic element of antenna array for base-station.
SIMULATION AND DESIGN
1. Dual-band Antenna
For improving the bandwidth and gain feature of monopole antenna with limited floor,
two copper sheets (parasitic element) are placed on both sides of the mono-pole with co-
plane structure, as shown in Fig.1. The structure is different from the one in literature[2].
The distance between monopole and two parasitic elements is much small. Stronger
current can be induced on two parasitic elements from monopole antenna. The dual-band
characteristic of the antenna is presented by properly adjusting the height, width of the
monopole and metal sheets on both sides, as well as the distance between them. The
simulation result of VSWR is shown in Fig.2, which covers two frequency bands of
1.9~2.55GHz and 3.35~3.6GHz respectively. The optimal VSWR performance is at
2.4GHz and 3.5GHz.
Due to the inductive current on metal sheets of both sides contributes to the radiation
of the antenna, the gain of the whole antenna is enhanced. The antenna shows two
resonant bands and its bandwidth is not wide enough, which limit its application greatly
such as MIMO, B3G, et al. The main reason limiting the bandwidth is the electrical
length of reflection board is two small. In fact, the monopole antenna in center is not
0-7803-8883-6/05/$20.00 ©2005 IEEE

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equivalent as a half-wave dipole. As shown in Fig.3 and Fig. 4, H-plane radiation pattern
keeps omni-direction with 3dB variation, E-plane 3dB beamwidth is 90 degree at 2.4GHz,
while the radiation pattern is broaden at 3.5GHz. It shows that the floor of dual-band
antenna is designed too small, so that it has no image effect at 2.4GHz and 3.5GHz.



Fig.1 The structure sketch of designed antenna Fig.2 VSWR simulation result of dual-band antenna
















Fig.3 E-plan radiation pattern Fig.4 H-plan radiation pattern

2. Wide-band Antenna
Keeping the size of the antenna and increasing the size of the metal floor, the VSWR
still display two frequency bands. The low band is greatly extended from 1.15GHz to
2.7GHz where VSWR is less than 2, which bandwidth reaches 80%. The bandwidth of
upper band achieves more than 300MHz. The simulation result of VSWR is shown in
Fig.5. If floor is assumed to be infinity electric plane, the metal sheet on both sides is
close to the center metal sheet fed, so the inductive current is contributed on them. It can
be seen their equivalent radius is thick and characteristic impedance is low. Furthermore,
the actual feeder of the center sheet is not at location of Z=0, so the sheet and its image
form an open line, while the sheets on both sides and their images form a short line.
Because the input impedance of the two lines has opposite characteristics, the imaginary
part of total input impedance is decreased [3].
The structure parameters of the antenna, such as S, H, W, have close relationship with
its bandwidth. The first resonant point appears at H=λ/4, and the height of the center
monopole antenna determines the passband location of low band. In 3.5GHz frequency

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band which is close to double of first resonant frequency, the influence of antenna height
on bandwidth is more apparent. Because wavelength in low band is longer, the variation
of H has small influence on performance of low band, but has obvious influence on
performance of upper band. It is quite different in high frequency band where the
increase of H results in decrease of the frequency and the drop amplitude is about
150MHz/2mm measured in experiment. The height and width of the metal sheets on both
sides are key parameters to get wide bandwidth and excellent impedance match.
Adjustment S influences mainly the location of the second resonant point. The resonant
frequency decreases with S increase, which influence is approximate 100MHz/1mm
measured in experiment. W is an important factor for the VSWR performance and
important parameter for wide band. There is optimal W value for special frequency band,
otherwise the VSWR performance will deteriorate and the bandwidth will be decreased.
The parameter S is adjusted to make the second resonant point move from low frequency
to high frequency, and restrain the imaginary part of input impedance at 3.1GHz.
Meanwhile H could be adjusted to keep feature at 3.5GHz. The VSWR performance of
the wide-band antenna is shown in Fig. 6, the frequency range covers 1.15GHz to
3.7GHz.

Fig.5 VSWR of dual-band antenna with Fig.6 VSWR of wide-band antenna
big reflection plane with big reflection plane

EXPERIMENTAL RESULTS

In this paper, the antenna with pole shape is made of copper sheet. The VSWR was
tested by network analyzer Agilent 8753ES SNA. The results are shown in Fig. 7-9. The
VSWR of the antenna is good in frequency about 2.4GHz and 3.5GHz. Increasing the
reflection plane’s size can improve the antenna’s bandwidth availably. They accorded
with those simulation results certainly well. At last, the ultra wide-band antenna covers
the frequency from 1.15GHz to 3.68GHz. The test results of VSWR are some better than
those simulation, because the loss of the two sheets metal is omitted in simulation, while
the loss improve the VSWR in measurement. The prototype of wide-band antenna is
shown in Fig.10.
CONCLUSION
In design of the wide-band low-cost antenna, the height H of the mono-pole, which
nearly equal to λ/4, determine the antenna’s first resonance frequency in the lower band.
For getting wide band and impedance match, the height and width of metal sheets on both
sides should be chosen properly, and the sheets with proper width on both sides should be
near feeder in center as close as possible. Because the reflection plane is not infinite in
fact, the size of the reflection plane affects the bandwidth of the antenna. From
experiment data, the diameter of the reflection should be great than two times of the
wavelength at center frequency at least for getting satisfied bandwidth.

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Fig.10 Dual-band VSWR Fig.11 Dual-band VSWR with large reflection plane







Fig.12 Wide-band VSWR Fig 13. Picture of Designed Antenna

REFERENCES
[1] Staff of Radio Research Laboratory of Havard University [M] Very high frequency
technique .1947
[2] Mao-Bing Wang, “Composite dipole radiation feature analyze”，Modern Radar,
No.2, Chinese, 1998
[3] Chao-Dong Zhou et al, “Antenna and waves”, Press of Xi’an University of Electronic
Technology, Chinese, 1999