Novel Design Method of Dual–Band Antenna for WLAN Applications
Ding-Bing Lin1 and Jian-Hung Lin2
Institute of Computer and Communication, National Taipei University of Technology
No. 1, Sec. 3, Chung-Hsiao E. Rd. Taipei 106, Taiwan, Republic of China
Email:1dblin@en.ntut.edu.tw, 2s2418035@ntut.edu.tw
Abstract － In this paper, we propose an alternative
method to design the antenna that performs as well as
PIFA antenna. The advantage of the designed antenna
compared with patch antenna is that the antenna size can
be also reduced 50% as PIFA antenna. Also, another
advantages of the designed antenna compared with
monopole antenna as well as microstrip antenna are planar
and no dielectric loss. If we, on the structure of the
designed antenna, place an additional patch near the signal
probe feed. Then the antenna possesses the dual-band
characteristics, 2.4GHz – 2.48GHz and 5.15GHz – 5.35GHz
for the bands of wireless local area networks (WLAN). In
other word, the designed antenna resonates at frequency
2.4GHz and 5.2GHz and possesses 8% and 11% bandwidth
respectively.
Index terms－dual-band antenna, PIFA, WLAN.
top plane
λ 4
h
bottom plane
ground plane
Fig. 1 side view of the novel antenna structure
L2
W1 Wg
In numerous antenna structures, microstrip patch
antenna is widely applied to design the antenna in ISM
band generally. It is because the advantages of the
microstrip patch antenna are low profile, lightweight and
low cost. Directly-fed microstrip patch antenna usually
have limited bandwidth about 2~4%. High dielectric
constant material is conducive to the reduction of
antenna size, but the problem of the radiation efficiency
and the limitation of the bandwidth will occur [1][2].
Therefore, on the consideration of the size and
bandwidth of the antenna, the microstrip patch antenna
structure is replaced with the PIFA (Planar Inverted F
Antenna) gradually. For PIFA antenna, the size and
bandwidth of the antenna will be reduced 50% and
improved by introducing one more shorting pin than
microstrip patch antenna [3]. PIFA antenna is a major
structure in compact antenna, and there are detailed
discussions in [4]-[6]. Also the PIFA antenna is usually
used in the design of dual band antenna [7]-[9] and
diversity antenna [10]. The feature of the PIFA antenna
is its quarter wavelength of the resonant frequency. This
advantage compared with monopole antenna as well as
microstrip antenna is planar and no dielectric loss,
g1 W2
x
W4
La
INTRODUCTION
With the rapid progress of wireless communication
systems which come in variety size ranging from small
hand-held devices to wireless local area networks. The
integration of different radio modules into the same
piece of equipment has created a need for multi-band
antenna. The antenna which can operate at two or more
frequency bands is more desirable and convenient.
Therefore, the design of compact and multi-band
antenna becomes a critical technique.
y
z
W3
Lg
I.
L3
L1 g 2
top plane
shorting pin
L4
ground plane
h
bottom plane
probe feed
Fig. 2 dual band antenna configuration
respectively. So we propose an alternative method in this
paper to design the antenna that performs as well as
PIFA antenna. And then, through the proposed antenna,
we design an antenna that possesses the dual-band
character used for the bands of WLAN.
II. ANTENNA STRUCTURE AND DESIGN
METHODOLOGY
Fig. 1 shows side view of the antenna structure
which is composed of two FR4 planes; the thickness of
the FR4 planes is 0.4mm, and the layout of the antenna
radiator on the top plane is shown in Fig. 2. The
dimension of the ground is 46 × 32 mm2 . The
geometrical parameters of the antenna are h = 6.8mm, L 1
= 8mm, L2 = 17mm, L3 = 6mm, L4 = 30mm, La =
21.5mm, Lg = 2.5mm, W1 = 21mm, W2 = 15.5mm, W3 =
5.5mm, W4 = 6mm, Wg = 6mm, g1 = 2mm, g2 = 8mm.
The probe is fed from cross position of the long and thin
radiator and the L-shape patch, while the short pin is
located at the center of the U-shape patch. Both patches
are coupled by an air gap with length Lg. The antenna
proposed in this paper provides two resonant frequencies
at 2.4GHz and 5.2GHz by the combination of two
resonators, one is the long and thin radiator and the other
is the L-shape patch.
(a)
(b)
Fig. 3 Current distribution at frequency (a) 2.4GHz (b) 5.2GHz.
The lower resonant frequency is determined by the
length of long and thin radiator and the length of air gap.
We set L 4 = λ 4 of the lower resonant frequency
2.4GHz, then tuning the appropriate length of air gap
and the appropriate dimensions of the U-shape patch for
a good impedance match on the lower resonant
frequency. For the fixed length L4, increasing the length
of air gap is equivalent to reducing the length of the long
and thin radiator. The simulation result of the current
distribution for the frequency 2.4 GHz is shown in Fig.
3-(a). In which, the current distribution on the long and
thin radiator shows the same direction. Both the current
distributions on the U-shape patch and the L-shape patch
show the opposite direction and flow into the node of
short pin or probe feed. Hence the dominant radiation
effect comes from the current distribution on the long
and thin radiator.
The higher resonant frequency is dominated by the
dimension of L-shape patch. In our design, we
set L2 + W2 = λ 2 of the higher resonant frequency
5.2GHz. Also, the air gap Lg and the U-shape patch are
needed to provide a good impedance on both resonant
frequencies. Observe the simulation results, shown in
Fig. 3-(b), of the current distribution for the higher
resonant frequency 5.2GHz. Both the current
distribution on long and thin radiator and L-shape patch
show the same direction, while the current distribution
of the U-shape patch shows the opposite direction and
flows into the node of the short pin. The dominant
radiation effect comes from the current distribution on
both the L-shape patch and the long and thin radiator.
Hence, not only the dimension of the L-shape patch will
affect the higher resonant frequency but also the length
of the long and thin radiator.
Through the above descriptions, the design procedure
can be summarized as the following:
1. To decide the length of L4 such that the antenna
resonates at the lower resonant frequency.
2. Tuning the dimensions W1, Wg and L of U-shape
patch and set a sufficient long air gap to get good
impedance on the lower resonant frequency.
3. Place an additional L-shape patch near the signal
probe feed and decide the length of L2+W2 such that
the antenna can also resonate at the higher resonant
frequency.
4. Tuning the length of long and thin radiator for fine
tuning the higher resonant frequency.
III. SIMUALTION AND MEASUREMENT RESULTS
The characteristics of the radiation can be
confirmed through the simulation software Ansoft
Ensemble using the analysis of moment method and the
automatic measurement system set up on an anechoic
chamber. Fig. 4 shows the simulation results of the
resistance and reactance of the dual-band antenna.
Figure 5 shows the simulation and measurement results
of return loss. The measurement results are good
agreement with the simulation results. And the designed
antenna resonates at frequencies 2.4GHz and 5.2GHz,
and the bandwidths are 200MHz and 600MHz
respectively. Figures 6 and 7 are the return loss for
different L2 and different Lg respectively. The shorter L2
increases the higher resonant frequency from 5.08 GHz
to 5.4 GHz. In addition, the longer air gap Lg, equivalent
to the shorter La for a fixed length L4, increases the
higher resonant frequency from 5.08 GHz to 5.34 GHz.
But, varying L2 and Lg has not impact on the lower
resonant frequency. Although the length Lg of air gap
will effect the impedance matching condition, that is
more insensitive than the dimension of U-shape patch. It
is found that the resonance frequencies can be adjusted
independently, which makes the design procedure
simpler.
Fig. 4. The impedance of the designed antenna
Fig. 6. The influence of the resonant frequency for
different L2
Fig. 5. Return loss of the simulation and measurement
results
Fig. 7. The influence of the resonant frequency for
different Lg
The measured radiation patterns are shown in Figs.
8-11. The antenna gains are 3.46dBi and 7dBi at
frequencies 2.4GHz and 5.2GHz, respectively. The
simpler design procedure has been pointed out in the
previous section.
and upper resonant frequencies as 8% and 11%
respectively. The experimental results obtained show
good radiation characteristics for two operating bands of
a WLAN antenna.
REFERENCE
IV. CONCLUSION
The novel design method of dual-band antenna is
introduced in this paper for wireless local area networks
applications at 2.4GHz and 5.2GHz bands. It can be
utilized to perform the multi-band or dual-band antenna
due to easy combination with other type antennas.
Moreover, both the two resonant frequencies can be
adjusted independently through the variations of the
parameters of the antenna dimension. The characteristics
of the radiation can be confirmed through the simulation
software Ansoft Ensemble and the automatic
measurement system. Therefore, the two resonant
frequencies can be designed individually which makes
the design procedure simpler. The bandwidths of the
designed dual-band antenna were found for the lower
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Fig. 8. xz-plane at 2.4GHz
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Fig. 9. yz-plane at 2.4GHz
.
Fig. 10. xz-plane at 5.2GHz
Fig. 11. yz-plane at 5.2GHz